I see that some barrel makers offer a one in 8" twist rate for their .277 barrel. What application doe it have?

KB

Good question. I called nosler and requested a 160 grain accubond for the 270 and they said that it would be to long to stabilize in the average 1 in 10 twist rifles.

What I don't get is, if their that concerned about the .277 caliber why in the heck do the make so many weights for the .308?

Longer bullets perform better with a faster twist rate for stabilization. Could it be (in the U.S.) as the bullet manufacturers move to lead free bullets that the barrel makers are providing barrels for the LONGER (for weight), monolithic bullets?

As is pointed out above "they said it would be to long to stabilize in the average 1 in 10 twist rifles" (with an accubond bullet - a mono in 160 grains would probably be even longer).

I think (I have no real experience) that this barrel is probably offered for the 6.8SPC cartridge. This slower velocity caliber would struggle with heavier for caliber bullets with the old standard 1/10" twist. The faster a bullet moves through a barrel the faster it spins, and the rate of spin is what determines how well it stablizes. This means that a slower moving bullet would need a faster rate of twist to compensate for this lower velocity.

quote:

Originally posted by boltshooter:
Longer bullets perform better with a faster twist rate for stabilization. Could it be (in the U.S.) as the bullet manufacturers move to lead free bullets that the barrel makers are providing barrels for the LONGER (for weight), monolithic bullets?

As is pointed out above "they said it would be to long to stabilize in the average 1 in 10 twist rifles" (with an accubond bullet - a mono in 160 grains would probably be even longer).

Yes but the monolithics don't offer any benefit from being heavier because they don't shed weight and their hollow point depth is the same across the bullet line providing identical expansion performance. They would be more effective if they drilled the heavier ones deeper allowing for greater expansion capability with the heavier weights.

The concept with the accubond is that it will continue to expand as long as it is moving through tissue making for a larger and longer wound channel. The Barnes bullets make the initial wound channel than it tapers off. The best analogy for this is to study wave movement at the beach. The motion of the water is pushed up by the rapid change in the floor depth. The greater this change the higher the wave. Bullets expand and the larger they expand the greater the wound cavity. Since the expansion is the same between the Barnes 150 grain 308 and the 180 grain 308 there is not significant benefit for using the larger bullet.

I always find these videos interesting.
http://www.barnesbullets.com/i...on/high-speed-video/ Look at the ones with the 6x6x16 ballistics gel.

There is one for the .308 130gr, and another for the .308 180 gr. Perhaps it's my imigination, but it looks like the 180 does more damage.

I sorta agree with Captain: "monolithics don't offer any benefit from being heavier because they don't shed weight". That's true within certain parameters. There is little doubt that a 180gr bullet will penetrate deeper than a 130gr bullet. That's what SD is all about. It seems to me that drilling the hole deeper for more expansion on the heavier bullets would be contrary to their penetration advantage, and the purpose of using a heavier bullet in the first place. Looks to me like the Barnes TTSX or TSX expands just right, with either the 130 or 180 gr. Only so much expansion is useful. If I wanted to hunt deer with my 308, looks like the 130 gr would be near perfect. If I wanted to hunt elk with my 308, it looks like the 180 gr would be near perfect. The 130 gr may not exit an elk, but most likely the 180 gr would. That's the way the bullets are designed to work, and I wouldn't change a thing. There is a definate benefit from useing a heavier bullet for elk.

Again, I sorta agree with the Captain: "The concept with the accubond is that it will continue to expand as long as it is moving through tissue making for a larger and longer wound channel." The part I disagree with is the longer wound channel. I firmly believe the Barnes mono bullet will make longer wound channels every time, compared to the AB. Also, the Captain is right that the AB is designed to lose weight. Perhaps it might be said that rather than by design, it couldn't be avoided by design. That's what all lead core bullets do, some more than others. That's what the Barnes TTSX is designed to not do. The lead core bonded bullets shed weight too, and thus SD, and thus penetration, as they pass. The AB is bonded, but has no partition, and the lead apparantly is the same hardness (or lack thereof) from front to back. The jacket is relatively thin, so surely it will shed weight in proportion to impact velocity. One lead core bonded bullet that retains a lot of its initial weight is the Swift A-frame, because it also has a partition.

So, another way to look at it is take the 200gr AB and 180gr TSX, both .308, shot from a 300 mag, same velocity. IMO, the TSX will penetrate deeper, and cause a greater wound channel than the 200 gr AB. Now, that's just an opinion, because I have no way to test it. It's based on the knowledge that the AB will shed weight, and the TSX will not.

I would expect the 200 gr TSX .308 bullet to exit a brown bear or moose, most times, and I would expect the 200gr AB to not exit most times, everything being equal, except the bullet.

BTW, I'm still interested in discussion of the 8" twist rate of .277 barrels.

KB

quote:

Originally posted by Captain Finlander:
Good question. I called nosler and requested a 160 grain accubond for the 270 and they said that it would be to long to stabilize in the average 1 in 10 twist rifles.

What I don't get is, if their that concerned about the .277 caliber why in the heck do the make so many weights for the .308?

quote:

Originally posted by Luckyducker:
I think (I have no real experience) that this barrel is probably offered for the 6.8SPC cartridge. This slower velocity caliber would struggle with heavier for caliber bullets with the old standard 1/10" twist. The faster a bullet moves through a barrel the faster it spins, and the rate of spin is what determines how well it stablizes. This means that a slower moving bullet would need a faster rate of twist to compensate for this lower velocity.

Nosler is correct. The AB bullet would be long in relation to the 160gr Partition. The partition 160gr apparantly barely stabilizes in a 10" twist. The slight additional length would cross the threshold and not be spinning fast enough.

That's the issue with the 270. 130gr - 140gr works well, and in some rifles not as well with the 150gr, and in most rifles not at all with anything heavier than 150gr.

The 308 barrels are commonly available in 10" twist and 12" twist, and several other twist rates for special purposes. So a broad range of bullet weights can be used, but generally not the full scope in any given barrel.

In theory the slower velocity needs a little faster twist to stabalize, but the 6.8mm std bullet is 115gr, which is light for caliber. So the faster twist theory doesn't apply to the 6.8mm. Even if 130gr bullets are used, 10" twist is plenty sufficient at the lower velocity. I've seen some barrels in 11" twist for the SPC, which is the correct way to go, rather than faster.

So, the 8" twist for. .277 barrels is not for the SPC.

So, my question is why the 8" twist rate for .277 barrels? Is it to shoot 150gr and heavier bullets? Is it that simple? There are lots of 150gr .277 bullets, and one 160gr, and even some real heavies from Woodleigh.

I don't know any other bullets for the .277, so I'm wondering why not a 9" twist rate. Do barrel makers simply like even numbers?

Perhaps thinking of the question this way will help: The main reasons I hear and read for the 6.5x06 is to shoot the 6.5mm bullets with their higher SD and BC. Heck, take the 270, with 150 gr bullets, and it would take some doing to tell the difference comparing a 6.5mm 140gr, and a 6.8mm 150gr, in the field or at the range. So, apparantly the 8" twist rate is popular with the 6.5x06 fans. Is this 8" twist rate in 6.8mm the answer to the comparison of the 6.5x06 compared to the 6.8x06?

KB

It is not possible to correct a bullet length/twist rate mismatch by adjusting the speed.

With a hollow point, boat tail bullet that is 1.15" long, the stability factor at the muzzle is 1.32 at 3700fps and 1.29 at 3100fps, from a standard .277" 1:10" twist.

From a 1:8" twist, the same bullet has a sf of 2.06 at 3700fps and 2.02 at 3100fps.

OK, Gerard, I'm going to say what you said, but presented differently.

1:10" twist / BT 1.15" long / SF = 1.32 at 3700fps / 1.29 at 3100fps

1: 8" twist / same bullet / SF = 2.06 at 3700fps / 2.02 at 3100fps

It's difficult to do tables in postings here.

BTW, Gerard, I cerainly don't want to be rude in any way to anyone with info on this subject, but may I tactfully say that I have had some difficulty in understanding some of your technical posts in the past. Please help me understand what you are saying.

I agree with your first sentence.

I have at least a couple of presumptions:

One is that "enough" SF is good, and more than enough is not necessarily better.

I am presuming this "stability factor" is a term useful for comparitive purposes, that can be computed accturately with any specific bullet, at any given velocity.

There are a few things I don't know about that subject, for example, what is the optimum SF for a 150 gr BT .277 bullet at 2800 fps? And what twist rate does it take to obtain that optimum SF? If we are going to get mathmatical, and scientific, then hypothetical is practically useless, and abstract is less than useless, but a distraction instead. Let's get specific, especially defining "enough" with regard to SF.

It is possible that this topic is a COW (can of worms). I did a quick google on stability factor / external ballistics, and found some light reading:

http://en.wikipedia.org/wiki/External_ballistics

http://www.longrangehunting.co...-big-deal-not-59552/

http://www.exteriorballistics....bexplained/index.cfm

http://www.jbmballistics.com/b...ller_stability_2.pdf

http://kwk.us/twist.html

http://www.jbmballistics.com/cgi-bin/jbmstab-5.1.cgi

Next, I'm going to look at some of the free ballistic software links, and see if they answer my questions.

The last link seems to answer the question: is the 10" twist fast enough for the 150gr .277 bullet? Apparantly yes, mathmatically, which may be something 270 owners already know from experience. I've never tested it thoroughly, other than one or two of the 270s I've owned apparantly shot 130gr bullets more accurately than 150gr. Those were very limited tests and several years ago.

I cross checked the formula by inputting data for .264 bullets, 9" twist rate, for the Norma 156gr, Lapua 155gr, and Hornady 140gr SST bullets. The Norma and Lapua are in the green stability factor, the Hornady is in the yellow. I don't know if I'm supposed to count the plastic tip of the SST in the length or not, but counting the tip, the 140 gr .264 SST is the longest of the three bullets. The heavy Norma and Lapua bullets shoot accurately in my CZ 550, 6.5x55, which has a 9" twist rate.

So, if 10" twist is fast enough, for normal .277 bullets, then what purpose does 8" twist have?

Thanks,
KB

KB
The 1:10 rifling certainly works with 150gr Sierra GameKing SPBT bullets, as I my mediocre marksmanship was getting just over 1MOA five shot groups with them a couple of months back.
Unfortunately I didn't get hold of the 160gr Nosler Partitions in time to see whether or not they stabilised. Hopefully I'll get to do this either in May or October.
I see there are some 170gr VLD's available too - more excuse for time at the range.

Thanks for the feedback and info. Every now and then, I take a look at the 270, to see if it can really fill some kind of precieved niche. Last one I had, I bought for a gift to a friend, but I wanted to keep it. It was an older CZ 550 with the round top receiver, and I was very impressed with its accuracy.

I just got back from the range sighting in two of my CZ 550s, one in 6.5x55, and the other in 7x57. I got three new Leupold 3x9x40mm scopes from Midway at the end of year sale/clearance. These rifles are so accurate that I'm sure it was the easiest range session I've ever had, sighting in. About five or six shots each, and it was done. These loads were previously developed with different scopes mounted.

Although I like the 270, I'm quite sure that I'll never be able to use the two rifles mentioned above sufficiently. And I have several others for use as well, equally or better accurate, like the 7x64 I sighted in last weekend. I need to sell some stuff, but I have a hard time doing that. I have a difficult time selling even an inaccurate rifle, because I always want to make it better.

KB

I don't know much about the mathmatics of SF and all that stuff, but over the years twist rates reflect the bullet lengths fired from the rifle.
Light wieght, shorter for the caliber bullets can use a slower twist. Heavier, longer bullets need a faster twist.
The 223 is a good example. A few years ago the 12-14 inch twist shot bullets from 40 to 55 grains very well. In the last few years much heavier, longer bullets have become very popular.
To shoot these bullets the rifles need a much faster twist. 7 inch twist is now the norm. And 80-90 gr bullets.
I think this trend is moving to other calibers. I have seen load data for the 270 using 180 gr bullets. If that 180 gr bullet is has a long tapered nose and a boat tail the 10 twist won't work.
It needs the 8 inch twist. With the increase in monolithic bullets and high ballistic coefficients, then maybe all calibers are going to get faster twist rates.

I suspect that chamberings like the 270 Allen Magnums and the like are the reason.

Even if not for those chamberings, bullets such as the Wildcat ULD bullets require fast twists and even the Berger VLD 150gr needs a 1 in 9 as I recall.

Also remember that altitude will affect what works and some guys prefer being slightly more comfrotable with their set up than on the ragged edge of stabilisation.

GS Custom manufacture a 120 & 130gr in their HV range, which need a 1:8 twist barrel in order to stabilise those projectiles.

Aren't the most significant parameters in bullet stability dynamics, bullet length & RPMs.

He He .............we just tend to talk about RPMs in terms of twist & velocity.........and put most of the emphasis on velocity.........simplifying tables of stability factors to highlight velocity.

Theres a bunch of things that affect stability but the really influential ones are bullet length & RPMs.

You can toss tables around in different ways but the bottom line is that a bullet of a given length requires a "window" of RPMs for optimal stability.
where less than the window is quite harmful , but more than enough is much less harmful to stability.
That being the case RPMs are determined by launch velocity & barrel twist.
Hence lower velocity requires a higher twist to achieve RPMs in the required "window" for a given length of bullet.
Both velocity & RPMs degrade with distance of travel from the muzzle( velocity more than RPMs) so stability at distance is influenced by launch velocity , but more by trans-sonic instability at distance than anything else in that mix of parameters in the overall dynamic of stable bullet flight.

Or did I miss something in ballistics study.

quote:

Originally posted by Kabluewy:
I see that some barrel makers offer a one in 8" twist rate for their .277 barrel. What application doe it have?

KB

To answer the original question. The 1:8" twist was developed specifically for those people who wanted to used heavier than normal for caliber bullets for extended long range shooting or hunting. The prime example was the Wildcat 169.5gr and 195gr .277 caliber bullets. These bullets are very long for their caliber. Much longer than the Barnes Original 180gr round nose bullet.

In Nolser reloading manual #1 1976 they published factory rifle twist for most calibers. They have a Mannlicher-Schoenauer for the 270 with a 1/9 twist barrel also a Husqvarna with a 1/9 1/2 twist barrel.

Here is what I found when looking up the 1:8 twist .277 barrel.

quote:

Re: 270 Allan Magnum?

--------------------------------------------------------------------------------

270yotekiller,

The 270 Allen Mag is based on the 7mm RUM case. Since I designed and built several of these rifles I have since become aware of some slight headspace variations in the 7mm RUM brass.

As such, I not recommend using 300 RUM brass as the parent case. This allows for a more positive shoulder to provide a gas seal should the original headspace measurement of the parent case be a bit short.

Basically with the 300 RUM case, you can set the correct headspace for the fireforming loads. With the 7mm RUM you are pretty much at the mercy of the factory spec ammo.

Also, using the Federal 300 RUM cases has also produced good results if you can find this bulk brass.

The 270 Allen Mag is best suited to the Rem 700 RUM receivers but any long action receiver can work as long as it has a magnum bolt face. I do recommend RUM receivers if a repeating rifle is desired.

Savage receivers work great but you will be limited to single shot rifles as the fat shoulder does not agree with the Savage magazine system, even in RUM chambered receivers.

I recommend Lilja barrels for all of my custom rifles. Any top quality barrel will work though. I did have Dan Lilja tool up to build 1-8 twist 3 groove barrels specifically for my 270 Allen Mag.

THis fast 1-8 twist will easily handle the big 169.5 gr ULD RBBT and there is also a 185 gr ULD RBBT in the works from Wildcat Bullets for this round as well as the new to be released 277 Allen Mag.

If you will be shooting conventional bullet weights, the standard 1-10 twist is great. In 30" barrels the 270 AM has been able to drive the 140 gr Accubond to 3625 fps!!! THis is a hot load but you may have read the report of a mountain goat recently hammered with this combo. Seemed to work great!!!

If you want the extreme range performance, the 1-8 twist is the best way to go as it will allow you to use the heavy 169.5 gr ULD RBBT as well as the new 185 gr ULD RBBT when it comes out. You can also use conventional bullets in this twist as well such as all the Ballistic Tips and the 140 gr Accubonds. Thin jacketed bullets may not be able to handle this fast twist.

Let me know if you have any other questions and I will give you all the information I have.

Kirby Allen(50)
__________________
Kirby Allen(50)

Allen Precision Shooting
Home of the Allen Magnum, Allen Xpress and Allen Tactical Wildcats and the Painkiller Muzzle brakes.

Farther, Faster and Flatter then ever before.


allenmagnum@gmail.com

Way back when, there were some 180gr round nose bullets made in .277.

IME the 1/10 stabalized anything up to 160grs just fine.

As for the 6.8 SPC, some barrels were designed with a 1/9 twist, probably because it's a popular twist in the .223 are variants. In reality, this is faster then needed in the 6.8 SPC and the 1/11 is a better choice in this chambering.

quote:

txhunter77

To answer the original question. The 1:8" twist was developed specifically for those people who wanted to used heavier than normal for caliber bullets for extended long range shooting or hunting. The prime example was the Wildcat 169.5gr and 195gr .277 caliber bullets. These bullets are very long for their caliber. Much longer than the Barnes Original 180gr round nose bullet.

Yep I can vouch for that,

The .270 Allen Magnum


Left to Right, 150gr Nosler Solid Base, 169.5gr Wildcat RBBT ULD, 195gr Wildcat RBBT ULD


195gr Wildcat...


195gr Wildcat @ 500yds, white spot is 2.5",


Loads for these run as follows, 150gr Nosler - 95grs of WC-872 3550fps, 94grs of WC-872 169.5gr WC RBBT ULD 3450fps, 92grs WC-872 195gr WC RBBT ULD 3250fps.

Mike, I like your style. Sounds like a Goat zapper to me.

quote:

Way back when, there were some 180gr round nose bullets made in .277.

IME the 1/10 stabalized anything up to 160grs just fine..

IME my 1977-vintage Ruger M77 stabilized the old Barnes 180s just fine. The RN profile made them shorter than some lighter, pointed bullets.



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