I decided to have my 308 re-barrelled in the same caliber but with a tighter twist. At the moment it only groups with 140 grains bullets, or lighter. I already own a 270 and most of my hunting is done in the bush. The rifle will be used mostly to hunt impala and warthogs for the table and for the occasional wildebeests / kudu / eland. There are dangerous animals in my hunting area and I have decided to use always 220/250 grains premium bullets at a moderate velocity. Maximum shooting distance will be 150 yards and I prefer over-stabilization to any risk of fish-tailing at short distances. Any suggestion on the most appropriate rate of twist? The barrel will be custom made on my specifications.

I have shot the 220 gr. Sierra Pro-hunter round nose bullets from a .308 Winchester M70 22" barrel which has a 1 in 12" twist with excellent results groups have run as small as .375" and as large as .75" from that rifle. velocity was 2310 FPS.
I have also shot the same bullet from a Ruger M77 RSI with 18.5" barrel and 1 in 10" twist for a velocity of 2250 FPS and groups in the 1.5" range. To be fair about it, the RSI is an extremely fussy rifle abut what goes down it's barrel.
I just had a custom 1909 Peruvian Mauser with Oberndorf action built up that has a 1 in 10" twist but have only just started doing load work up with this rifle.
I don't know what powdersyou have available, but my load were worked up using Winchester's W-760.
Data is as follows:
Start: 42.0 gr. 2177 FPS 42,000 C.U.P.
Maximum: 44.0 gr. 2295 FPS 46,900 C.U.P.

Note the low pressure figure for the maximum load. I did my work up during the Southern Arizona summer which as you probably already know is hotter than hell. According to my notes, it was about 105 degrees "F" at the time of shooting.
My velocity figures were chronographed, and the average of five rounds. At no time did I experience any signs of high pressure. Brass was Winchester once fired and I used the Winchester standard Primers.
I obtained the data from an earlier One Book/One Caliber loading manual. Later copies completely ignore bullets heavier than 200 grains. Data with other powders did not even come close to the velocity level of W-760 with a very very few exceptions.
Hopethis was of some help.
Paul B.

Hi Paul,
thanks. Based on your esperience 1 in 10" twist will do it. I'm not looking for high velocities but for security reasons I want the bullet stabilized within a couple of yards from muzzle. My new barrel will be 18". I like a short barrel in the bush and therefore I'm particularly interested in the results obtained with your M77.

Has anyone tried a 1 in 8" twist? I will mostly shoot rhino or GS bullets, that are slightly longer than average.

why don't you just rebarell in 358 win and forgo all the hasell?
it's just a 308 necked up to 35 cal,and handles bullets up to 250 grs just fine.

Since most large case .30 calibers are 1 in 10", the mere existence of 250 gr bullets indicated that this twist in a new barrel with a good crown was adequate. The original .30-03 was designed with 1 in 10" specifically for 220 gr round nose in a military application wear a certain amount of crown wear was to be expected. Most .308 long range target shooters go from 1 in 12" to 1 in 11" to better handle 190 gr BTHP when their original barrel wears out. for 220-250 gr 1 in 10" is clearly indicated.

There can be no arguement that for the pupose you state for this rifle, on paper the .358 Win would be the ideal choice. It is a splendid cartridge for tough game at moderate range. But I cannot imagine trying to find .358 ammo in South Africa. Its far from common even in the U.S. You will always be able to find .308, even if it isn't you favored heavy bullet load.

Brazos Jack

in South Africa re-licensing a new barrel in the same caliber is a lot easier than obtaining a licence for a different caliber and I already own a 9,3 x 62 carbine that is grouping 0,25" at 90 yards.

On the other hand the 358 Win has a very good reputation in South Africa for bush hunting and maybe to change from a "military" caliber to a "strange" one is not going to be too difficult.

If I can locate a source of good 9 mm bullets in South Africa I will definitively consider the suggestion.

i would imagine woodleighs are available.

Berger recommends 1 in 11 on their looooong 210VLDs.

I have fired 250 Barnes and 220 Sierras out of both 1 in 10 and 1 in 11 barrels with good accuracy.

I can't imagine in a hunting .308 you'd need a 1 in 8,
the bullet to benefit from that could be as long as your pinky finger and take up all your powder space

I have been reading a very interesting article http://www.gsgroup.co.za/articlepvdw.html. It has been written in regard to solid bullets but the principles will be applicable to a soft bullet showing limited espansion.

My re-barreled rifle will be used only for hunting in the bush warthogs and antelopes up to the size of a kudu. In order to kill those animals with an hart/lungs shot a 130 grains bullet is more than adequate.

Main reason to use heavier bullets is because in the same hunting area it is possible to encounter buffalos, elephants and a variety of cats. As a consequence deep in line penetration becomes the main factor.

I think that a long 308 bullet at a moderate velocity will penetrate more and will stay in course better than a 358 bullet of the same weight.

Regarding the rate of twist it may better for me to go for a faster rate because longe range accuracy will be not required (for that I have a 270 and 7mm RM) while a good stabilization at 2 yards may save my life.

I noticed the 375 H&H key-holing at 5 yards and it was a good enough reason for me not to like the caliber.

Is any way to calculate the maximum twist to give to a 220 grains, 308 caliber, bullet without having the "nose up" effect showing before 150 yards? What will happen after that distance it is not my main concern.

Andrea,

I agree that you should not take chances on twist rate on a hunting rifle. Slightly too fast will slightly degrade long range accuracy and slightly increase rate of wear and jacket metal fouling. But slightly too slow combined with a little throat or crown wear and you'll keyhole so badly that you can't hit a flock of barns.

Don

The standard 1.12" twist will handle every bullet up to the 220-grain round nose designs. If yours is only handling 140-grain bullets, something is wrong besides twist....

Most of my shots are taken below 90 yards. I own long range rifles so, in this particular case, I'm only interested in short range accuracy and in-line penetration.

I've been reloading for many years and all my rifles groups within 1/3 of an inch at 100 metres. In my experience each rifle twist is providing the best accuracy with a particular bullet lenght.

My 270 is grouping exeptionaly well with Sierra and AFrame 130 grains but it is not doing so well with longer bullets. The same apply to other calibres when you go for the best accuracy.

I will hunt open sights but I will develop the loads with a 12 X scope and I want all shots trough the same hole at 50 metres.

Assuming that I want to use 220 grains Rhino or 177 HV which is the rate of twist that will secure the best short range accuracy, no fish-tailing and maximum in-line penetration?

I'm investing a sensible amount of money in this project and I want to avoid the risk of instally a barrel capable to produce only 1" groups at 100 yards with the bullet of my choice. Any expert advice?

quote:

Originally posted by Andrea Sandri-Boriani:
------Assuming that I want to use 220 grains Rhino or 177 HV which is the rate of twist that will secure the best short range accuracy, no fish-tailing and maximum in-line penetration?

I'm investing a sensible amount of money in this project and I want to avoid the risk of instally a barrel capable to produce only 1" groups at 100 yards with the bullet of my choice. Any expert advice?

Why not ask GS about the 177 HV
http://www.gsgroup.co.za/contact.html
and Rhino about the 220
http://www.rhinobullets.co.za/
directly?

Of course only address each about their respective projectiles- and not each others--

here is Gerard's opinion:

Hello Andrea,
In my first reply I said: "The 130gr HV outperforms jacketed lead bullets up to220gr at short range, with better straight line penetration, deeper penetration and larger wound channel volumes."

This is contrary to conventional thinking which dictates that long heavy bullets be used for short range bush work. This is one of those cases where conventional thinking has no basis in fact, when it comes to mono bullets.

The reason why slow and heavy lead core bullets are traditionally used for close up work, is to reduce bullet breakage on impact. Light, fast moving lead core bullets often shatter on impact and choosing slow and heavy is really choosing the lesser of two evils. Slow and heavy deflects easier and is more prone to tumbling. Fast and light shatters too easily. So, with lead core bullets, slow and heavy works more frequently than light and fast for close range impacts. Neither are the best solution.

With monos, bullet breakage is no longer a factor to consider - even the worst breakage still leaves us with excellent retention.

Here are the facts:
1. For short range and bush work, bullets with high stability factors are more reliable than bullets with low stability factors. Such bullets are less likely to deflect and will always penetrate straighter and deeper.
2. Given the same twist, the longer the bullet, the lower the stability factor and the shorter the bullet, the higher the stability factor.
3. There are four ways to increase the stability factor of a bullet.
a. Use a shorter bullet. (This makes the bullet lighter.)
b. Increase the spin rate by increasing the velocity. (The lighter the bullet, the higher the speed that can be achieved.)
c. Move the centre of gravity of the bullet rearwards. (Shorter bullets have shorter boat tails that shift the CG rearwards and a hollow point does the same.)
d. Tighten the twist rate of the barrel.

Compare the specifications of the 130gr HV with the 177gr HV and you will see what I mean.
So, if you are building a pure short range .30 caliber rifle, make it a ten or eight inch twist and use our 130gr hollow point at a brisk speed. That is as good as it gets.

Regards
Gerard

here is ALL correspondence with Gerard regarding this issue:

Hello Andrea,
In my first reply I said: "The 130gr HV outperforms jacketed lead bullets up to220gr at short range, with better straight line penetration, deeper penetration and larger wound channel volumes."

This is contrary to conventional thinking which dictates that long heavy bullets be used for short range bush work. This is one of those cases where conventional thinking has no basis in fact, when it comes to mono bullets.

The reason why slow and heavy lead core bullets are traditionally used for close up work, is to reduce bullet breakage on impact. Light, fast moving lead core bullets often shatter on impact and choosing slow and heavy is really choosing the lesser of two evils. Slow and heavy deflects easier and is more prone to tumbling. Fast and light shatters too easily. So, with lead core bullets, slow and heavy works more frequently than light and fast for close range impacts. Neither are the best solution.

With monos, bullet breakage is no longer a factor to consider - even the worst breakage still leaves us with excellent retention.

Here are the facts:
1. For short range and bush work, bullets with high stability factors are more reliable than bullets with low stability factors. Such bullets are less likely to deflect and will always penetrate straighter and deeper.
2. Given the same twist, the longer the bullet, the lower the stability factor and the shorter the bullet, the higher the stability factor.
3. There are four ways to increase the stability factor of a bullet.
a. Use a shorter bullet. (This makes the bullet lighter.)
b. Increase the spin rate by increasing the velocity. (The lighter the bullet, the higher the speed that can be achieved.)
c. Move the centre of gravity of the bullet rearwards. (Shorter bullets have shorter boat tails that shift the CG rearwards and a hollow point does the same.)
d. Tighten the twist rate of the barrel.

Compare the specifications of the 130gr HV with the 177gr HV and you will see what I mean.
So, if you are building a pure short range .30 caliber rifle, make it a ten or eight inch twist and use our 130gr hollow point at a brisk speed. That is as good as it gets.

Regards
Gerard


Hunting (Phalaborwa.net) wrote:
Hi Gerard

thanks, here is Marta, me and the kudu. We met in ’97 in a tour and ... we are still together! Come and visit us in Phalaborwa if you can. The rifle is Marta’s 9,3 x 62 but I’m using it more than her.

Our usual load is a 270 grains Speer bullets at 2.100 f/s and at 100 metres the shots are touching. At this velocity the recoil is very moderate and we never experienced bullet failure.

Only problem experienced so far have been an occasional but severe deflection by grass or foliage.

The only bullet that consistently is shooting straight in the bush is your FN, that I use with the 458 Lott. The problem is that, as I’m getting older, the rifle is getting heavier.

My shooting distance is very seldom above 50 metres and on the 308 I plan to have the rear sight installed more forward than usual. In this way it will be easier and quick to focus.

The general idea is for me to spend more time in the bush so I will not be needing to take every hunting opportunity but only the most favourable.

I’m thinking of a long, heavy bullet at reduced velocity, possibly over stabilized and capable of expanding about 1,5 its diameter up to 100 metres, but no more. Once desired expansion is reached the goal is to maximize in line penetration.

What about a 177 grains HV at about 2.500 f/s? Will it expand enough at the maximum range?

What it will be the optimum twist rate for short distance work? I have other rifles to be used at long range.

Best regards

Andrea

From: Gerard Schultz [mailto:gerard@wol.co.za]
Sent: 19 June 2009 10:04 AM
To: Hunting (Phalaborwa.net)
Subject: Re: best bullet - twist combination

Hello Andrea,
It is good to hear from you, are you keeping well?

If your shooting distance will not exceed 300/400m, then you can make the twist as tight as what you can get. As twist tightens, terminal performance will increase. In our range we recommend using the 130gr HV in a 1:10" or 1:8" twist and to run it on the high side - around 3000fps from 18" barrel. The 130gr HV outperforms jacketed lead bullets up to220gr at short range, with better straight line penetration, deeper penetration and larger wound channel volumes. Meat damage is also at a very acceptable level. For brute penetration, use the 145gr FN. It will go amazingly deep in very large animals even from a 308 Win. Wound channel volume is reduced from that of the 130gr HV but penetration is something else. We originally designed the bullet for elephant culling by Parks using R1 semi-auto rifles. In an 18" barrel one would use a fast burning powder to minimise muzzle blast and recoil. S335 with a magnum primer would work well.

If I can help with anything, just let me know.

Regards
Gerard

Hunting (Phalaborwa.net) wrote:
Dear Gerard

I need your advice. I’m re-barrelling a 308 rifle for bush hunting. At the moment it gives very good accuracy only with 130 grains bullets and I have already a 270 and a 7 mm RM.

I want an 18” barrel carbine, easy to carry in the bush, fitted with open fibre-optic front sight and adjustable rear sight. A 12 X scope will be used only for load development.

The stock is an original pre-war II civilian Mauser with the right drop for open sight shooting.

I will be hunting in the bush near Phalaborwa warthogs, impala, wildebeest and kudu. Absolute maximum shooting distance will 150 metres. Most of the shots will be below 50 metres.

As in the area there are buffalos, cats and sometimes elephants, I’m looking for the best possible combination of “bullet choice / rate of twist” for maximum on line penetration, compatible with the primary objective that is hunting non dangerous animals in the bush.

The idea is to choose the best possible bullet first, considering that no long range accuracy is required and that I like moderate loads, and then decide the best rate of twist for that particular bullet. What do you suggest?

My very best regards

Andrea Sandri-Boriani




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Shilen recommends 1:10 for up to 220s and 1:8 for over 220.

http://www.shilen.com/calibersAndTwists.html

Did you receive any input from Rhino?

Hi Ray,

rifling in military weapons is optimized for long range shooting. If on a 308 a twist 1:12 is the best for 140 grains bullets, my impression is that 1:10 will be the best "long range" twist for 180/220 grainers but will not "overstabilize" it for best short distance accuracy and on line penetration.

Apparently no one have been working so far on the "maximum" rate of twist that will still provide acceptable accuracy at 90 yards.

In my life I have used an handgun for self-defence in 3 occasion and I never shot an attacker that was more than 2 yards from me.

I assume that if I will have to use the 308 for self-defence it will be at a very close range and I've seen many hunting calibres key-holing under five yards.

A charging animal, a marginal caliber and a fish-tailing bullet is a very bad combination.

In addition, the major problem when hunting in this area is deflection by grass or foliage. I hope that an overstabilized bullet will also have a more stable path.

Maybe I will have to consider a progressive twist, starting from 1:12 and ending 1:6. I did write to Rhino Bullets but received no answer.

Hey Andrea, Sounds like an interesting Project that you are asking about. My questions to you might complicate things a bit, but it is better to have thought through this stuff up front rather than after you have purchased the barrel.

1. Do you have access to a 165gr and 180gr Nosler Partition, one of the 220gr, and one of the 250gr Bullets you mentioned? Two of each is even better.
2. Do you have access to a tool which will allow you to "Section"(remove part of) a Case Wall without collapsing the entire Case.

If so, I'd encourage you to Section 4 previously fired Cases(do not resize the Case Necks), slightly Crimp the Case Mouth on each with a set of pliers and Seat one of each Bullet inside the Sectioned Case. Make sure they are all below 2.8" in overall length if you are using a Short Action.

You can pre-discover some interesting things. First of course the heavier Bullets take up a whole lot of the Case. And some real long Bullets have to be Seated so deeply that the Case Neck is now "trying to grip" the Ogive. I have no idea if that is the situation with the Bullets of your choice or not.

As for me, if a 165gr Nosler Partition in a 308Win is not adequate for the Game being Hunted, then it is time for me to step-up to a more robust Cartridge. But, I can see where a person(not me) might use the 180gr Nosler Partition.

Best of luck on the Project though. And if that is still what you want to do after trying the Sectioned Cases, I hope it all works out great for you. If it doesn't, you can always re-re-barrel it.

Here's putting it in perspective.

The photo below is a 308 case with a Sierra Game King 180gr Flat base bullet loaded to a col of 71mm/2.8". The additional lines show where the base of a 220gr round nosed flat base, a 200gr spitser boat tail and a 240gr hollow point boat tail match bullet would be, loaded to the same col.



This photo shows the 180gr Sierra loaded to 71mm/2.8" col, a 130gr HV loaded to 70mm/2.76" col and a 177gr HV loaded to 74mm/2.91" col.

Andrea;

Search for "greenhill formula", which is a link to a program that allows you to input your bullet diameter, length and weight as well as velocity to determine optimal twist rate.

Also, as others have alluded, if your 1-12 308 barrel will not stabilize mid-weight bullets, there probably is more than just twist rate involved. 1-12 should stabilze up to 175grain or so bullets in 30 cal. Remember, though, velocity and twist rate both factor in for bullet RPM, too short a tube and not enough velocity (especially with a mid-sized round like the 762x51 or 308 Win) with a big bullet may not get enought spin to stabilze well I would expect that with a 200 grain bullet and a 18 inch barrel, you may only get 2100 FPS, hence a 1-10 or even faster twist may be required.

For your stated purpose of medium game and maybe a DG or cat in a pinch, I'd bet a 200 grain Nosler Partition would do just fine, although one hole accuracy may be tough... Minute of heart or brain (on soft game, not buff) at 50m, no doubt would be easy.

As far as a 375 keyholing at any range closer than maybe 800-900 m (well below supersonic) with a normal bullet (250-350 grains) would be a question for a gunsmith- a bad crown or completely worn rifling would be my first guess.

Too bad your country is so restrictive on cailbers/gun possession, as a medium 30 cal (30/06 up to 338/358/9.3) would fill your requirement very nicely!

The 9.3 would fit in that category as well, I'd think, and provide a level of ability even the heaviest of .30 bullets in 308 win (at low velocity) would not be able to provide.

God Bless and best wishes!

Hey Gerard, Thank you for the flicks. That did indeed get across what I was trying to convey.

Would you happen to know if any of the Heavier Bullets that Andrea is considering would create the Case Neck/Ogive problem?
-----

By the way Andrea, I've not seen a single person "with any sense at all" say anything bad about Gerard's Bullets. Always nice to use a Company's products near you when you can.

The CIP/SAAMI spec for col and case length of the 308 Win suggests a maximum nose/ogive length of 20mm/0.79". Col can of course be set at any length that the rifle will allow, depending on the length of the magazine box and the amount of freebore.

Using the CIP/SAAMI as a guideline, any bullet with more than 20mm/0.79" ogive length would put part of the ogive inside the neck or would have to be seated longer.

Best is to measure the suggested bullets to determine nose, shaft and overall bullet length.

Determining the shaft length and shaft position of a bullet is relatively easy. Place a piece of fine sandpaper on a flat surface and wipe the bullet firmly and flat against the sandpaper. The resulting line defines the shaft dimension quite well.

Interesting how between 7mm 130hv & .30cal 130hv [both 1:8 twist]the SF virtually doubles for .30cal

quote:

If your shooting distance will not exceed 300/400m, then you can make the twist as tight as what you can get. As twist tightens, terminal performance will increase. In our range we recommend using the 130gr HV in a 1:10" or 1:8" twist and to run it on the high side - around 3000fps from 18" barrel. The 130gr HV outperforms jacketed lead bullets up to220gr at short range, with better straight line penetration, deeper penetration and larger wound channel volumes

Gerard, in reference to short range, what distance do mean?
Im just trying to figure to what distance I could get the type of 130hv performace you mention above, from .300weatherby.

Thanks to all!

I'm learning a lot of interesting stuff and I will try to put it to good use.

To Hot Core:

my 308 is based on a military K98 action. It can accommodate long bullets provided they have parallel sides. Alternatively I will be forced to have the chamber reamed to 30 06 and re licenced.

To Andrew Cempa:

the problem is to find the best twist/bullet combination for maximum accuracy at 50 yards and acceptable accuracy at 90 yards, under the assumption that an overstabilized bullet will provide better short range accuracy.

My main objective is to avoid foliage deflection and maximize on-line penetration with a 308 caliber rifle fitted with an 18" barrel.

The fundamentals of the project are the caliber and the barrel lenght. The purpose of the excercise is to determine the twist rate and the choice of bullet.

So far probably the most sensible route is the one suggested by Gerard of a ligh, fast monometal bullet at maximum velocity on a standard 1:10 barrel.

Most of my hunting at the moment is done with a scoped 9,3x62 using a 270 grains Speer bullet at 2100 f/s.

All other cartriges loaded in the magazine are solids at 2.600 f/s.

I never had bullet failures and the accuracy at 100 yards is 1/3 of an inch most of the times out of my short barreled CZ (gunsmith accuratized) carbine.

The only problem have been the occasional bullet deflection by grass/foliage. On the range, shooting trough grass have produced about 1 flyer out of 7 shots.

The 308 project will allow me to walk in the bush with a lighter, unscoped, rifle still adequate for my normal hunting.

Remember that I live in this area and I can afford to "pass" a difficult shot. I'm also only shooting for meat and this make the whole thing lot easier.

I've been using GS bullets on my 270 since 1995 and I found them very effective from springbok up to gemsbok.

My 308 existing military barrel, shortened to 18", is very accurate with 130 grains bullets, particularly SAKO factory bullets. Heavier bullets are laving the barrel spiralling and they only start to provide decent groups at about 300 yards.

I have been using Nosler Partition bullets in the past with mixed results. Besides cats, in this hunting area there are often buffalos and elephants. It is for this reason that I'm looking for deep in-line penetration, just "in case".

My (limited) experience with 375 did show some form of key-holing (from light to very bad) with different rifles every time the target was closer than 5 yards.

In my opinion it has to do with the caliber and the rate of twist adopted by manufactures.

Assuming that I will decide to hunt with a 130 grains GS HV bullet, using GS FN 145 grains as a back-up, what is going to be the maximum advisable rate of twist that will still provide accuracy at 150 yards?

I assume that monolitic bullets being omogeneus will allow some amount of over stabilization. What about barrel wear and throat erosion? Is 1:10 an adequate compromise or is it worth to try 1:8?

Trax,
We see short range as any distance at which tractibility is not important. This is any distance at which the bullet is not compromised in terminal performance, if it does not follow (nose over) the bow of the trajectory. With a 308 Win and our 130gr HV, short range is muzzle to 300/400m in a 10 or 8 inch twist.

High stability factors accentuate bullet imbalance and target shooters tend to choose the slowest twist that allows stable flight with jackted lead core bullets. Turned copper monos do not have this potential imbalance problem and high stability factors will not affect accuracy. Often the mistake is made to assume that, if good accuracy is obtained on paper with slower twist rates, that good terminal results will follow.

quote:

my 308 is based on a military K98 action. It can accommodate long bullets provided they have parallel sides. Alternatively I will be forced to have the chamber reamed to 30 06 and re licenced.

I understand. Darn shame about that Law and the rechambering, but I see what you are trying to do.

If you go with a fast enough twist, perhaps you could use Gerards Bullets as well as those Heavy ones you were thinking about. Always nice to have many options available.

Good Hunting and clean 1-shot Kills.
-----

Hey Gerard, Great Tip about the Sandpaper. As soon as I saw it, it reminded me of something similar to that one of my Elders had mentioned to me a very long time ago.

It appears that the best compromise is going to be an 8" linear twist, that will work well with light copper bullets at high velocity (because of the low imbalance factor of GS bullets) and, in case of necessity, will also work with long conventional bullets at a reduced speed.

Any suggestion for a barrel manufaturer that can provide a good quality barrel in 8" twist?

quote:

Originally posted by Andrea Sandri-Boriani:
Any suggestion for a barrel manufaturer that can provide a good quality barrel in 8" twist?

Shilen = http://www.shilen.com

I have fitted a number of Shilen barrels and everyone was a shooter. In SA, it is much more of a matter of what is available, rather than what one prefers. Magnum Arms in Nelspruit usually have a good selection of Walther and Walther Match barrels in stock and Truvelo in Midrand also have good stock levels and do a pretty good job. Go to someone who has a selection of barrels available. Lately there is the temptation to recommend what is in stock, rather than what is right or required.

I heard today that Peter Meszarich in Kimberly also carries a good selection of barrels.

Hi Gerard

the gun is already at Magnum Arms in Nelspruit!

Eugene wanted to fit a 1:10 twist, probably because he had one in stock, but I was not convinced so I asked for advice on the Forum and I'm glad that I did it.

I changed my mind!

Eventually is going to be 1:10 twist. Here are te reasons:

1) Gerard convinced me that long bullets are more prone to thumble on game and 1:10 will overstabilize nicely short bullets like the GS Custom 145 grains FN or the GS Custom 130 grains HV

2) The twist is about right for the 180 grains PMP AFRICAN ELITE, that is a good conventional factory load using Swift A-Frame bullets

3) I found in my cupboard 800 X 150 grains Speer bullets of the same batch, more than adequate for hunting game up to Wildebeest and Kudu + 300 X 125 grains Sako solids. Those bullets will work better in a 1:10 than 1:8 twist.

4) and (probably the most important factor), the barrel with 1:10 twist is already in stock at Magnum Arms and I may be able to test the rebarreled gun during the current hunting season

quote:

The twist is about right for the 180 grains PMP AFRICAN ELITE, that is a good conventional factory load using Swift A-Frame bullets

You should not be having sleepless nights over your choice of a 10-inch twist barrel for your 308 Win, as that is commonly fitted to a 30-06 Spr and not a 308 Win. Given the short case of the 308 Win you are not going to go heavier than 180 grain bullets, and frankly you don't need to for medium game. Even more so, if you choose a quality controlled expansion bullet like a Swift A-Frame. Going to an 8-inch twist is superfluous and will not give you any practical benefits in the hunting field, based on the notion that its higher SF number will give you supposed straighter and deeper penetration. In fact PMP loads their 180 gr lead-core bullets for the 308 Win, and it is very popular amongst SA hunters that buy ammo over the counter, bearing in mind that the slower 12-inch twist is perhaps the most common barrel twist for the 308 Win, and yet no stability problems whatsoever are encountered. So a 10" twist is more than ample. Chasing the highest SF number possible is a moot endeavour in my opinion.

Here are some bullet lengths to ponder over:

Sierra 165 gr SPBT ------- 30.12 mm
Sierra 180 gr SP ---------- 30.14 mm
Hornady 180 gr RN ------- 29.67 mm
PMP SP ProAmm ---------- 29.90 mm
Swift A-Frame 180 gr ---- 30.86 mm
Nosler Part. SP 180 gr -- 31.75 mm

They are all very close to each other

And now expanding monolithics:

GS-HV 130 gr -------------- 29.70 mm
Barnes-X 150 gr ---------- 30.61 mm

And these are pretty close as well, none being too long for a .308 chambering.

I shot a Blesbuck with a .308 Win (1-in-12" twist) recently, loaded to a MV of 2,900 fps, a heart-shot at 250 yds, impact velocity 2,300 fps with a 130 gr GS-HV bullet (BC=.370 and not .430 as shown in Quickload), and it performed well; the way I like a bullet to perform ... well expanded with intact petals, thanks to a modest striking velocity at range, keeping the bullet inside its threshold strength - slightly over-expanded and not quite symetrical as we see with the Barnes-X, but it performed well and held together. I will publish the bullet later when I have chance to photograph it. The buck dropped in its tracks, and the bullet was retrieved on the opposite side, just under the skin. I cut the bullet out with my knife right there in the field, as I saw the buldge under the skin. Once again it proved my believe that a modest impact velocity is best; in line with the operating window of a bullet. Incidently, getting back to SF values, the SF of the bullet in this case is only about 1.6 and a far cry from "dubbel this number" and more, for supposed reliable straight-line penetration. ( http://www.gsgroup.co.za/308130HV080.html )

I agree, for "dangerous game" one should be looking at heavier bullets in a bigger caliber, just for comfort.

Warrior

Pontificus Erroneus

quote:

Originally posted by Andrea Sandri-Boriani:
Hi Gerard

the gun is already at Magnum Arms in Nelspruit!

Eugene wanted to fit a 1:10 twist, probably because he had one in stock, but I was not convinced so I asked for advice on the Forum and I'm glad that I did it.

Good choice.
A barrel to handle most .308 bullets with good results.

This is not addressed to Gerard (SA RASPUTIN), but for the benefit of AR readers:

With reference to ART ALPHIN as mentioned by the South African RASPUTIN .... "Art Alphin of A Square also reported deeper straight line penetration of solids with a faster twist." .... Alf wrote the following and I suppose Gerard must stand in opposition to this, as he elected not to quote Alf, but rather to support Art Alphin.

This was Alf's response at the time:

"With all respect to Mr Alphin but the scientific ballisitcs literature does not support this notion.

IN fact I would put it to you that the section on the Mechanics of bullet penetration page 117 of any Shot you want is full of blatant unfounded error. It is typical of the junk science that permeated popular hunting magazines for years. From the explanations of the "toothpaste effect" shown in the picture in the middle of page 120 right down to to his assumption that his round nosed monometal solids somehow do not become unstable in target.

He then goes on to quote Mike LeGranges wood baffle box and the assumptions made from shooting 460 Weatherby's and 458 Win mags into the wood....... how basic can it be, does he not know that there is a huge difference between a solid like wood and and viscoelatic material like flesh in terms of the relationship between velocity resitance to penetration? In fact has this person even bothered to ask what constitutes a solid, a fluid, soft solid, visco-elaticity before attmpting to contemplate what effects a penetrating bullet would have on each?

Even the explanation of how and why a soft nosed bullet deforms up to a point and then stops deforming is devoid of any scientific explantion.

The reason round ball shoot "better" with spin has nothing to do with stability, round balls cannot be unstable because a perfectly round ball has it's centre of geometry ( or centre of form) at the same point as the centre of gravity.

The spinning of a round ball reduces surface drag by creating turbulent flow conditions around the ball and thus better long range performance, add dimples to the ball and it gets even better... hence the golfball. Spinning a ball reduces drag not "improve on stability"

No the fact is that "Normal" twist angles within the limits of what we normally see in rifles with commonly used bullets at usual hunting distances do little to influence impact conditions as far as penetration goes and thus in target behaviour of solid bullets. And this is supported by good evidence in the scientific publications dealing with aeroballistics."

I value Alf's explanations a hundred fold more than Art's, and thus I am not shy to quote Alf, as Alf always try to base his explanations on scientific principles, from which most of us can learn, except the present day RASPUTIN who runs his own agenda.

Warrior

quote:

slightly over-expanded and not quite symetrical as we see with the Barnes-X, but it performed well and held together. I will publish the bullet later when I have chance to photograph it.

Here are some pictures of the .308/130 gr HV referred to showing non symetrical expansion and over-expansion that I will contrast with a .277/130 gr Barnes-X bullet also impacting at 2,307 fps and retrieved from a kudu. There is no criticism here, just the way it actually is, and how these two competing expanding monolithic bullets have performed on game at similar velocities.

It is clear that the HV bullet is not as strong by design, and thus it will lose petals earlier, as we push impact velocites further up. In all fairness, as I have mentioned in the past, the HV bullet is a precision lathe-turned bullet unlike the Barnes-X, but here we talk about the terminal effect, which is largely determined by the design, i.e. shape and size (depth & diameter) of the hole drilled hole in the tip of these copper bullets; thus the thickness of the copper petals vary. When design criteria differ, it follows that bullet behaviour will differ.

TOP VIEW - HV BULLET:



SIDE VIEW - HV BULLET:



THE BARNES-X Bullet



Warrior

quote:

Originally posted by Andrea Sandri-Boriani:
Most of my shots are taken below 90 yards. I own long range rifles so, in this particular case, I'm only interested in short range accuracy and in-line penetration.

I've been reloading for many years and all my rifles groups within 1/3 of an inch at 100 metres. In my experience each rifle twist is providing the best accuracy with a particular bullet lenght.

My 270 is grouping exeptionaly well with Sierra and AFrame 130 grains but it is not doing so well with longer bullets. The same apply to other calibres when you go for the best accuracy.

I will hunt open sights but I will develop the loads with a 12 X scope and I want all shots trough the same hole at 50 metres.

Assuming that I want to use 220 grains Rhino or 177 HV which is the rate of twist that will secure the best short range accuracy, no fish-tailing and maximum in-line penetration?

I'm investing a sensible amount of money in this project and I want to avoid the risk of instally a barrel capable to produce only 1" groups at 100 yards with the bullet of my choice. Any expert advice?

Rifles which consistantly produce 1/3" groups at 100 meters are exceptional! The difference between a 1/10 vs a 1/12 twist for a 308 will not be 1" vs 1/3"! This difference depends on how well the barrel is rifled and installed on your action, including the stock bedding job!

BUT, if you are shooting solids, the faster twist will tend to keep the bullet on a straight path after impact. For expanding bullets, the shape of the expanded portion has more to do with straight line penetration than does the twist rate.

to El Deguello

both my 270 and 9.3x62 have produced groups of less than 1/3" at 100 metres. Both rifles have been accuratized by a competent gunsmith, I spent a lot of time in developing the best loads and I reload my hunting ammunitions the same way I will do for a benchrest competition, using all the tricks of the trade.

When I shoot for grouping I use a concrete bench, bench rest accessories, an high power scope and I cool down the barrel between shots.

Still 1/3" groups are just the best that I occasionally manage to obtain, with most of the groups of the most accurate loads averaging about 1/2" at 100 metres.

My main reasons for a tighter twist is to avoid fish-tailing at short distance, possibly to have less deflections from grass/foliage ont the bullet path and to obtain more in line penetration with GS bullets.

The 308, with the actual 18" barrel 1:12 twist shoot well at short distance up to 130 grains. Heavier bullets are all spiralling and fish-tailing well over 100 metres and group reasonably well only from about 200 metres.

As the 308 is going only to be used for short distance work I'm prepared to trade long range accuracy for better performance below 100 yards.

To Warrior

thanks for the advice. I live in South Africa and passed my exames as PH some years ago. I've been reloading and shooting 308s for more than 20 years and I'm quite familiar with the bullets you have mentioned.

I found them perfectly suitable for shooting a kudu or a wildebeest but I've seen them tumble in many occasions.

After hearing Gerard arguments I'm convinced that I will obtain better in line pentration using short bullets of a very solid construction.

The 1:12 twist commonly used on 308 rifles secure the best long range accuracy with 140 grains bullets on a standard barrel lenght.

On my rifle (18" barrel) 130 grains factory Sako are producing 1/2" groups at 100 metres while 180 grains PMP factory (or reloaded) ammunitions always produced groups of 2" or grater, showing on the target that the longer bullets at that distance where not yet properly stabilized.

The accuracy was better at 200 metres, proving that the short range inaccuracy was indeed due to under-stabilization.