...WORK to get to be close to feeding!!


Just picked up my ruger mkI 7remmag today, from Invader66, and put some bullets (shorten oal to 3.35 by seating bullets deeper) in 375 rum brass. put 3 down and closed the bolt over 3 down... it'll never get 4 down, without parts, but 3 down and about 20 mins with a file, and it will hold in the box correctly. Or just bend the mag box a little ...

This will be the first 470 ar chassis, i hope!!

Chadd is wanting a 416 in a blr.. heh..

jeffe

jeffe,

Well, tell Chadd to hurry up and get one, a BLR that is. So that the "Bubbas" can field test it here and report to the "Big Bore Forum" how well it works.

Hog Killer

thanks for the positive report...

keep on trucking

"AR Rounds ... Ain't Much"

This thread title gave a glimmer of hope that Jeffe had seen the light, but I see that's wrong. What a tease!

Well, I hope to see this pig fly!
Repent! Get thee behind me BUM Brass!
It's a bum rush to save a few pennies on brass.
I too am a cheapskate, but not so silly, not RUM drunk!!!

Sure enough Ron.. I've seen the light, and it's cheap brass, common actions, and easy feeding.

I love dave's 470 mbogo.. Probably the best all around african round, for those will to train with it, as it has it all, hi MV, hi SD, exellent bullet construction, and a decent bullet selection. It will far out perform anything made off a RUM case...

as will the 450 rigby

416 rigby

30, 338, and if there aint one there needs to be, a 375 lapua...

470 mbogo
450 riby
460 weatherby (same case, with a belt)
416 rigby
416 weatherby
375xlapua
378 weatherby
338 lapua
338x378 weatherby
308 lapua
30x378 weatherby...

Excellent rounds all, amazingly well designed (well, the weatherby's are too high of pressure)

and you have an extremely limited number and selection of actions to build from.

But, that's why there's opinions and horseracing.. everyone like to have them, and there's usually a gamble against the outcome.


In our case, the world gets the payout, either way.

jeffe

Jeffe,
Just playing devil's advocate.
I am sure you can make it work right on up to .470 AR, using the same tricks as with the .400 Brown-Whelen and .411 Hawk.

Y'all have fun making brass.
I've got too many wildcats to feed already.

Hi Jeff
I'm taking it that the filing etc was to get the cartridges into the magazine to feed up the magazine box. I'll be interested to see how much work it will be with the file etc to get them to feed into the chamber. Please keep us informed.
Take care,
Dave

Who would you reccommend to rebarrel a Browning BLR to 470AR? I would start with whatever was most suitable BLR caliber. Butt and forearm would seem to lend themselves to adding weight as necessary.

glad to see the africa blr catching on

I would like to reiterate a concern about the very slow twist rates being used for these rounds. Keep in mind that these rounds will be able to generate some pretty good velocities. But with the historical slow twist rates being used (such as 1:18 for the .470 AR), bullet yaw will be significant. That is not a problem for a bullet travelling through air as the bullets will not keyhole on a target. But once the bullets strike game they are likely to tumble quickly, resulting in reduced penetration.

This is the same problem that the old .460 Wbys faced, which contributed to their early reputation as relatively poor penetrators.

The solution to the problem is simple: use a faster twist barrel. Personally I would opt for a 1:10 twist for optimal stability of bullets in game, and for the ability that such a fast twist provides for extra heavy bullets. While it is true that faster twists increase pressure, the pressure increase is not significant and will only be an issue if the cartridge is already loaded to red line.

The other solution is to keep velocities down to 2100 fps where standard weight bullets did well with a relatively slow twist rate.

For more information about using faster rifling twist to achieve deeper bullet penetration in game, see the A-Square reloading manual entitled "Any Shot You Want".

grains...talk to jeffeosso regarding this...see what he will do about this

Not a problem as Pac-Nor has several twists in .475, the fastest being 1-10.

1-10 sounds quick, I'd think 1-14 would be more like it.

Hi 500grains,
I'm a little confused with your last post. The 1 in 18 twist is the standard for the 470 Nitro with a 500 grain bullet and it seems to work just fine. Keep in mind that a 500 grain bullet in .475 is shorter than a .458-500 grain bullet. Do you think that the 470 AR will be loaded with heavier bullets than the 500's or do you think that the fifty or one hundred feet per second gain in velocity is the problem. The original project goal was 500 grain bullet at 2200 fps or has that changed? I don't see your concern. The actual barrel twist rate on the rifle tested in the A-Square manual is 20.98.
Take care,
Dave

Dave,

We both know that people are going to push these rounds well past 2200 fps.

And the concern is shallow bullet penetration caused by excessive yaw.

As to the original 20.98 twist for 470 NE, a couple of points. First of all, the historical results for the 470 NE were not all that spectactular, which is why several of the old time hunters like Taylor preferred the 476 NE. Second, push the velocity up and you get... excessive yaw and shallow penetration.

All of this was proven in the field when the 460 wby got started. No need to re-trod those footsteps.

Hi 500 grains,
What would you consider the main contributor to cause yaw or the bullet sleep theory. I think it is the crown not the twist rate. The bullet is turning as fast when it leaves the barrel as it will during it's flight so why would it be unstable for the first portion of it's flight (30 yards) and then be OK. If the crown is perfect the bullet will leave evenly, If the crown is bad the bullet will leave one portion while the other portion is still engaged causing the bullet to yaw. I did a test which is on my site to see if this yaw or sleep affected bullet penetration. I loaded a cartridge and shot it point blank, at 25 yards and at 50 yards with the IMPACT velocity being the same or as close to it as you can get. All the bullets ended up in the same board penetration wise. I think the 460 Weatherby was just ahead of bullet technology and if you tried the same test today with todays bullets the results would be totally different. The 460 is a penetrator pure and simple.When you mention the history of the 470 you also again have to look at the history of bullet design.
I still don't think you have a concern.
Take care,
Dave

quote:

We both know that people are going to push these rounds well past 2200 fps.

true true

Dan,
these are designed for moderate pressure.. if a fella wanted to run them faster, they should realise this, the pressure issues from the load and the faster twist, and plan his rifle from there.

I do think that they COULD go faster, if they are loaded up in pressure. Those guys know who they are, and should know themselves

For the record, a .475 bullet will stabilize at from from 800 to 2800 in a ~20 twist..

458 only needs an 18 for useful ranges

the 416 needs a 16..

I will be converting a ruger 77mkI, and 2 mausers, 470, 458, 416 in that order.

BLR barrels? call pacnor!!

No doubt I'll find an FN sooner or later, and a push feed model 70.

Do I think they CAN go faster than 2200? yeah,.. I think at 2200, though, a 9# rifle ....


jeffe

OK, I tried.

Good luck with the project.

(P.S. Boards are not animal flesh.)

quote:

Originally posted by 470 Mbogo:
Hi 500 grains, If the crown is perfect the bullet will leave evenly, If the crown is bad the bullet will leave one portion while the other portion is still engaged causing the bullet to yaw. I did a test which is on my site to see if this yaw or sleep affected bullet penetration.
Dave

Sir,

I do not understand why You would do an experiment like this? A crown MUST be perfect at any time, if not the bullet will wobble through its flight, wich results in poor accuracy and penetration. This is widely known, or have I misunderstood You in any way?

I must say I agree with 500grains on this one,
twist is more critical than many believes and the main reason for bullet yaw.

sincerely,

Dan,
I hear ya.. nothing simulates an animal shot but shooting an animal.. but.. there's a hook.. to have a PERFECT example, you would need 100 genetic twins (which I know a couple companies here in Texas that can work that out in cattle)

So, I would propose that we all mature our views of experimental datum. If the experiment can be repeated, the experiment is valid. The conclusion is actually the only thing we can dicuss at that point.

Bent,
There's several "understoods" that we must to to have perfect flight. Perhaps those are equal.. Dave has found that the crown is MORE equal in regards to penetration. Never, in his results does he say that these are to be extrapolated to animals. In fact, he says "this is plywood, not game" He and Chris and Chris did some very thorough testing, along the lines of Townsen Whelen's famous works.

Please read this link
http://www.470mbogo.com/BigBores/BigBores11.html

Sure, it's not flesh.. and you can repeat these test in normay as easily as I can in texas.. which, as you know, makes the TESTS valid, but the conclusions are to the user.

Interestingly enough, one would assume the crown, the crimp, the arc (at impart) and velocity would be as critical in penetration as it is in grouping.



I ought to change my tag line to "the 470Mbogo is the perfect all around African rifle"

and it will have a little brother... the 470 AR

jeffe

Jeffe, Dave,

I think we talked around each other. This test I find very interesting and makes all the sence in the world to me. Testing in plywood is of course not flesh, but it is a constant medium and will give each bullet equal resistance.

I reacted at Dave's talk about the crown and how an uneven one would result in yaw. I concluded an uneven crown must not erxist on any firearm, and therefore should not be paid any atention. A wrong twist will, on the other hand, effect the bullet from muzzle to target and is fairly common. Even with a perfect crown it is normal to have an ustable bullet at the first 30 yards, but this is getting tecnical an I would have to take time to write about it. In the end, we probably would end up agreed!

It has been 15 years since my days at Colorado School of Trades, and my english is not longer what it used to be - please forgive me for having to ask twice at some subjects, and thanks for all answers.

Bent,
don't me to have a conflict, just a debate

Here's where we agree, i believe
for accuracy
the crown, velociy, crimp, seating depth, barrel pressure and trigger pull must repeat exactly.

Within the confines of penetration (not accuracy)

Here's where I think we also agree
a bad crown can induce yaw, which is bad for penetration. By penetration I am taking accuracy as an assumed (the bullet hit the target)

This is where Dave's point on crown and penetration comes in.. I think we all agree, a badly yawing bullet will veer off

This is where I think we can agree to disagree in places. And I think it's only a matter of theory vs application, I hope i explain this well.

in a "perfect" gun, that a bullet's yaw in the first X range will change penetration.

What I mean by this is, if a bullet is yawing (sloughing, actually, as yaw is left/right in aeronautic terms, sloughing is left/right/up/down) then the bore or twist is WRONG (keyholing is a demonstration of bad yawing) or the bullet has a weight/balance problem.

We agree that if these factors exist, the bullet will have penetration issues.

Okay..

What Dave set out to prove is that, in fact, a well designed gun (twist being the variable) that the difference between 25 yards and 50 yards is of no importance in practical matters.

The picture with bullets stuck in the same board from 25 and 50 yards shows this imperically.

So, we all agree that if a yaw condition exists, it would have an effect. Dave's data demonstrates that the yaw condition is not within the commonly accepted "25 yards"...

Here's what I think about bullet's "going to sleep"...
1: after the first bullet length of rifling, the bullet is fully engraved with the rifling and has established the spin RATE

2: higher RPMS around an axis USUALLY means a higher dynamic stability..

3: the RPMS of the bullet are based on the twist of the rifle (rpms imparted) and NOT on the velocity of the round outside the barrel. Why? the spin has no effective drag to slow the SPIN vector down. The velocity of the round DOES slow, due to air drag. BUT the RPM is only fighting gravity, not air (as a major factor)

4: turbulence of the bullet hitting the air, assuming a proper twist, imparts FAR more yaw that the rifling, once the bullet is out of the barrel.


With those in mind, we can agree that
a bullet does indeed "yaw" as it exits the barrel. However, I do not agree that the distance required to stablize in the air is more than a few feet, vs many yards.

In fact, I would state that TWIST (say 18 vs 10 if 22 is enough) has very little to do with the yaw, as I firmly believe it's imparted by the nose of the bullet on air. and is more of a function of velocity than RPM

That a bullet flies like an arrow (twisting down an axis, bending and oscillating down range) is probably true.. BEHIND the nose and it's contact with the air... and is the same from muzzle to target, at any reasonable difference....

Of course, I could be entirely wrong, and the guys that report better groups at 300 than 100 (in terms of MOA) might be right.. but I doubt it and haven't experienced it.

jeffe

quote:

I ought to change my tag line to "the 470Mbogo is the perfect all around African rifle"

and it will have a little brother... the 470 AR

true true

Hi Jeff,
The shots into the boards were at point blank, 25 yards and 50 yards not just 25 and 50. If I had a 460 Weatherby I would do all the old test people keep refering to over again with quality bullets to put that one to sleep also.
Take care and see you soon,
Dave

Dave,
you know, I totally forgot the point blank part..

470Mbogo's little brother

Dave,

The penetration problems with the .460 Wby were in game, not boards. So it will not be possible to put that history to sleep by shooting boards.

Nor does anything posted on this thread establish that the AR rounds will not suffer from exactly the same problem. In fact, the AR rounds are just repeating history. If they just go to the shooting range, no problem. But if you guys plan to hunt buff, hippo or elephant with them, then a re-think of twist rate is in order. Dave, since you have the A2 reloading manual, you might want to read what Mr. Alphin wrote on the subject.

Further, no one has stated a good reason for using a slow twist such as 1:18 in these calibers (other than stubbornness). Why intentionally design a new cartridge with inferior specifications? If someone knowingly dos that for his own rifle, that's fine.

But for public consumption, the cartridges should be thought through a bit better, in particular the twist rate and rebated rim should both be addressed.

quote:

Posted 28 October 2005 06:12
Dave,

The penetration problems with the .460 Wby were in game, not boards. So it will not be possible to put that history to sleep by shooting boards.

500 grain
It is exactly as you've said the problems were in game "BULLET PROBLEM"
Yes I have the manual and have read it all. Keep in mind the author also designed the lion load bullet for soft skinned game and praises it through out his book. Field results suggest a different picture with poor penetration and surface wounds. He also makes crap brass but praises that also. So everything you read isn't gospel. You have to indulge yourself and try things out. I'm not dissagreeing that other twist rates should be looked at I'm just saying that the 1 in 18 will work. Keep in mind again that the .475-500 grain bullet is a short bullet. If you were looking at shooting a 560 grain then you should go to a faster twist. The 1 in 10 twist will increase pressures and the higher rate of rotation or a higher rate of surface feet per minute if you prefer will also be more violent to the design structure of the bullets designed for the .475 caliber. Maybe the 14 twist is a good compromise.
Take care
Dave

Just a little more insight to twist rate. Both of my 470 Mbogo's as well as Canuck's are 1 in 16 twist. Canuck's which was my original has pass throughs on Buffalo, frontal shots that penetrated ftom the chest to the hip cavity. This is with a Swift A-Frame. My new 470 with the same twist rate has penetrated Eland with a quartering shot that turned the rear hip bone to powder and carried on to just under the hide in the middle of the off rib cage. The other shot was a clear pass through. This was with a 500 grain Barnes X loaded to 2400 fps and the shot was at 175 yards. So let call the impact velocity 2200 fps. That's not plywood.
Take care,
Dave

quote:

Originally posted by 470 Mbogo:

quote:

Posted 28 October 2005 06:12
Dave,

The penetration problems with the .460 Wby were in game, not boards. So it will not be possible to put that history to sleep by shooting boards.

500 grain
It is exactly as you've said the problems were in game "BULLET PROBLEM"
Yes I have the manual and have read it all. Keep in mind the author also designed the lion load bullet for soft skinned game and praises it through out his book. Field results suggest a different picture with poor penetration and surface wounds. He also makes crap brass but praises that also. So everything you read isn't gospel. You have to indulge yourself and try things out. I'm not dissagreeing that other twist rates should be looked at I'm just saying that the 1 in 18 will work. Keep in mind again that the .475-500 grain bullet is a short bullet. If you were looking at shooting a 560 grain then you should go to a faster twist. The 1 in 10 twist will increase pressures and the higher rate of rotation or a higher rate of surface feet per minute if you prefer will also be more violent to the design structure of the bullets designed for the .475 caliber. Maybe the 14 twist is a good compromise.
Take care
Dave

quote:

designed the lion load bullet

quote:

He also makes crap brass but praises that also

You sure your not talking about
A-Square

quote:

.475-500 grain bullet is a short bullet.

You do know you can make that same bullet longer with out lossing any of the design qualitys.. and retain the weight..

Martin

quote:

Originally posted by MartinPotts:

quote:

.475-500 grain bullet is a short bullet.

You do know you can make that same bullet longer with out lossing any of the design qualitys.. and retain the weight..

Martin

Make it look like Bob Hope?

Hog Killer

Art Alphin used a 10" twist on his .470 Capstick in his loading manual for pressure data. Great data there. Great book.

I shoot a 10" twist .470 Capstick with 500 grainers at over 2300 fps.

I also have a 16" twist .470 Mbogo that is just beginning to get some steam up at 2500 fps with 500 grainers, and will certainly out-do the .460 Weatherby by actually clocking 2700 fps with 500 grainers, without blowing a gasket.

I would agree with 500grains' recommendation on twist, EXCEPT: the slower the velocity, the faster the twist needs to be.

The Mbogo with 16" twist is a good thing.

The .470 AR with a 10" twist would also be a good thing, and Art Alphin's .470 Capstick data would be a good place to start with it: H4895 Extreme will likely be a great powder for it.

The .470 NE in 18" twist is also a good thing, and penetrates just as well with FN solid 500 grainers at 2100 fps, in the Iron Buffalo. But of course that is not live buffalo.

It is hard to get too much twist in a hunting rifle barrel, especially if you hunt at ranges less than 1000 yards.

I would rather have more than enough twist.

Remember when they switched from smoothbore muskets to rifles? Bet Ray does.

Nice thing is, we are "down" to talking about the easiest thing in the world for someone to choose when they order their barrel!!

quote:

Originally posted by RIP:
The Mbogo with 16" twist is a good thing.

The .470 AR with a 10" twist would also be a good thing, and Art Alphin's .470 Capstick data would be a good place to start with it: H4895 Extreme will likely be a great powder for it.

The .470 NE in 18" twist is also a good thing, and penetrates just as well with FN solid 500 grainers at 2100 fps, in the Iron Buffalo. But of course that is not live buffalo.

It is hard to get too much twist in a hunting rifle barrel, especially if you hunt at ranges less than 1000 yards.

I would rather have more than enough twist.

Remember when they switched from smoothbore muskets to rifles? Bet Ray does.

Jesus, Ron, that last bit made me inhale coffee!!!

You know he was standing around on rock waiting for dirt to be invented!!

So, 1x18 at 2150 is good, 1x16 at 2500 is good and 1 x10 at 2300 is good.

So, I'll say "as long as the gun owner orders between 1x18 and 1x10 it's ALL good"

Now, as to why (it aint stubornness) I am going to use the "next" slowest twist I can... in MY guns..

Let's see, Ackley, Whelen, and OConner all talk a good deal (in small places) about twist. A too fast than required twist increased pressure (dramaticly, if you go too much) with a less increase in velocity than the same load in a slower twist barrel,NORMALLY.

I then proved that to myself with a series of 358 winchester barrels, 16, 12, and 10 twist.

So, we'll assume an OVERLY long 475 bullet, of 1.5 "
1500 fps - required twist 22.6
3000 fps - required twist 27.1
2200 fps - required twist 22.6

Chosen twist - 18 for my barrel

pac-nor offers .475 barrels in 10, 16, 18, and 25 twist.. with 18 being more than 70% of sales..
Remember, part of the goal here is 2200 at morderate pressure. That's the success criterion. And engineering (not just stubornness) leads me to choose all the "stuff" that will help.

jeffe

Guys,

I did not set out to step on any toes when bringing this up, and I tried to hold my tongue for a while. But I am afraid there remains a basic misunderstanding of the physics involved by some folks posting.

If you are going to offer up a new cartridge design to the public, why not take the time to do it right?

_________

Dave,

You mischaracterize the early 460 wby problem. True, there were bullet failures. Also there were serious penetration problems with solids not related to bullet failures. Wby addressed the problem in part by increasing the twist rate. But even with the slightly faster twist, using full house loads the 460 Wby is not such a great tool, which is why most PHs using it download to 2400 fps where the bullet is more stable. Starting to see the light? Unstable at 2650 fps but stable at 2400 fps. If you want the bullet to be stable at a higher velocity, INCREASE THE TWIST RATE.

As for how softs perform on plains game, that is useful data beause a soft reduces in length immediately upon entering the animal, which MAY permit it to overcome the problem posed by a slow twist. The real problem comes when ultra-long monolithics, such as the Barnes solid are used.

And the problem does not occur every time, so one data point of success does not disprove many data points of failure. The objective in designing a cartridge should be to arrive at a solution that WORKS EVERY TIME.

I am afraid my comments are falling on deaf ears because some guys have already built guns with slow twist barrels.

_______________


Jeffe,

All that you have said pertains to stabilizing bullets in air, not keeping the bullet stable while it travels through a game animal. O'Connor and Ackley wanted velocity, period. Further, neither one of them was an expert on the penetration of solids in large game animals, so reliance on their comments would be misplaced.

As for pac-nor sales, don't you think that 70$ of their .470 barrels are used to build .470 NE rifles, which seldom even exceed 2100 fps with factory loads?

But your .470 AR round will easily hit 2400 fps, and I am betting that some smart reloaders will push it well above that level. Thus the problem is clearly forseeable.

_________________


Once again, good luck with the project, but I think it is a disservice to the public to recommend a slow twist when that has proven to be a problem in the past with calibers capable of high velocity, and when the solution is extremely simple and costs nothing extra. Shifting the responsibility to the guy building the rifle is not a proper way to handle the dilemma either, as most gun nuts do not understand the influence that rifling twist has on terminal ballistics.

Recommendation: 1:10 twist. Pressure will not be a problem if the load is worked up with that twist. Velocity will still go well beyond the intended 2200 fps level.

______________

Now, what about the rebated rim on the Rum cartridges? It seems that the solution so that problem is to base the cartridge design on the 404 Jeffery case instead.

Dan,
i do appreciate the feedback. I'll see in a month or so what the 470 can do.. and probably have a working 416 and 458 quickly behind.

If someone wanted to do a faster twist one than I am building, it would be interesting to compare the results.

the serious stubborness I am holding to is moderate pressure. The case will be ~ that of the 416 rem, 458 lott, and 470 capstick.. perhaps more effecient, and at the same pressure (which i think is slightly too high)


the AB 416 and458 barrels (read - CHEAP) are 1x14... too bad they don't make a 475

jeffe

To increase bullet stability AT ANY VELOCITY: use a FASTER TWIST. This makes the bullet spin faster. This gives the bullet BETTER GYROSCOPIC STABILITY. This is not too much of a good thing until out way beyond 1000 yards when the bullet is still holding to the original bore axis alignment instead of nosing down and following the parabolic trajectory for better accuracy.

At less than 1000 yards range, i.e., hunting range: The more spin the merrier, as long as the bullet doesn't disintegrate in the air or on impact.

Sure, milking it down to just the slowest twisted needed for maximum long range accuracy depends mainly on length of the bullet in relation to caliber. Ho Hum after a certain point.

The lower the muzzle velocity, for any given twist rate, the slower the bullet will spin.

If MV is SLOWER, you need a FASTER twist rate to get equal RPS at any impact linear velocity down range.

All of this ignores the fragility of expanding bullets. Talking solids here for simplicity.

That said, I think that the effects of Twist on stability after impact are minimal, might make a tiny difference, and more twist will help more than hurt, if the bullet is a good one.

Also, I think the effects of twist on pressure are way over-blown. It just doesn't make much difference.

I would go for anything between 10" and 18" twist, for your .470 AR, and I would use the faster twist rate with the slower muzzle velocity.

I would prefer a 10" or 12" twist on any barrel of caliber: .375, .416, .423, .458, .475, or .510

That is all I have bought in the last few years from Harry McGowen, Douglas, and Dan Lilja.

McGowen deserves more acclaim. Best Quality, as is Lilja.

I couldn't get a faster twist than 16" from Pac Nor at the time I bought my .470 Mbogo barrel. It worked out well at the higher muzzle velocity of the Mbogo anyway.

My next barrel in .423 is going to be my third McGowen in that caliber, all 10" twist.

Guy's!! guys .. hold up here..
Are you building a 470x50BMG or a 470AR

At speeds of 2200 FPS you could use a freaking mico grooved like marlin did and put a
1x22 twist and at 100 yards you would never know the diffrents or a 1x10 twist.
We arn't talking about making a about making a
25x378 weatherby here. Nor is it a 600 OK

All things aside this is a nice 200 yard rilfe maybe.. or a close in brush buster with enough force to stop most anything here in the US.

Dan i understand what your saying ..i really do guy .. and its a good call on your part .. but
i dont think this is the next 475 A & M
Or 7MM Super Van Hoffman

Martin

quote:

Originally posted by RIP:
To increase bullet stability AT ANY VELOCITY: use a FASTER TWIST. This makes the bullet spin faster. This gives the bullet BETTER GYROSCOPIC STABILITY. This is not too much of a good thing until out way beyond 1000 yards when the bullet is still holding to the original bore axis alignment instead of nosing down and following the parabolic trajectory for better accuracy.

At less than 1000 yards range, i.e., hunting range: The more spin the merrier, as long as the bullet doesn't disintegrate in the air or on impact.

Sure, milking it down to just the slowest twisted needed for maximum long range accuracy depends mainly on length of the bullet in relation to caliber. Ho Hum after a certain point.

The lower the muzzle velocity, for any given twist rate, the slower the bullet will spin.

If MV is SLOWER, you need a FASTER twist rate to get equal RPS at any impact linear velocity down range.

All of this ignores the fragility of expanding bullets. Talking solids here for simplicity.

That said, I think that the effects of Twist on stability after impact are minimal, might make a tiny difference, and more twist will help more than hurt, if the bullet is a good one.

Also, I think the effects of twist on pressure are way over-blown. It just doesn't make much difference.

I would go for anything between 10" and 18" twist, for your .470 AR, and I would use the faster twist rate with the slower muzzle velocity.

I would prefer a 10" or 12" twist on any barrel of caliber: .375, .416, .423, .458, .475, or .510

That is all I have bought in the last few years from Harry McGowen, Douglas, and Dan Lilja.

McGowen deserves more acclaim. Best Quality, as is Lilja.

I couldn't get a faster twist than 16" from Pac Nor at the time I bought my .470 Mbogo barrel. It worked out well at the higher muzzle velocity of the Mbogo anyway.

My next barrel in .423 is going to be my third McGowen in that caliber, all 10" twist.

What?

quote:

Oringinally posted by 500grains:
...most PHs using it download to 2400 fps where the bullet is more stable. Starting to see the light? Unstable at 2650 fps but stable at 2400 fps. If you want the bullet to be stable at a higher velocity, INCREASE THE TWIST RATE.

500gr, That sure goes against a lot of writing on the subject. I always understood that you could do two things to improve stability with a particular bullet...1. increase twist rate or 2. increase velocity.

As an example...my 6.5 Gibbs with a 10" twist shoots nice little groups with 140gr bullets at all ranges. And it penetrates on game far more than I ever expected. I have always understood that it does this because I am pushing them 300 to 400 fps faster than a 6.5x55 that needs a 9 or 8.5" twist to accomplish the same thing.

The theory works in my little mind, because the faster you push the bullet in a given twist, the higher the RPM.

Now, to be clear, my response here has nothing to do with my 470 Mbogo having a 16" twist. Embarassingly enough, I never had a clue what it was until Dave E. mentioned it above.

I am only posting on this because your statement above has potentially turned my understanding on the topic upside down. More expalanation of your 460 WBY theory would be very much appreciated.

Cheers,
Canuck

Hey 500 grains,
From Your A-Square manual directly from your Guru Mr. Alphin. "In the past the 460 has suffered from a lack of bullets, especially soft points, that would hold together at such high velocities, remembering that most .458-inch bullets have been designed to perform at 458 Winchester Magnum velocities. These days there are both solids and softpoints that will perform at 460 Weatherby Magnum speeds. With bullets like the Dead Tough Soft Point and the Monolithic Solid the 460 Weatherby Magnum is, in practice as well as theory, one of the most impressive cartridges for use on dangerous game. Proffessional hunters who rely upon it maintain that the 460 Weatherby is, along with the fast 50's (500 Jeffery, 500 A-Square, etc), the 577 NE and the 600 NE, in that very select group that will literally flatten a Cape Buffalo. And of course, a good solid will reach an Elephant's vitals from any reasonable angle. Fred Duckwrth, the professional hunter based in the Netherlands, told me he has had legthwise exits on cape buffalo with his 460 Weatherby using A-Squares ammunition with the Monolothic Solid. That's 6 to 7 feet of penetration (in a straight line with no deflection, Fred adds) which is certainly enough for any animal.It also shows that A-Squares slightly lower, but realistic, velocities do not detract from the performance of the cartridge.
"SEE THE LIGHT" "BULLET PROBLEM "
The rifle a 460 Weatherby with a 1 in 15.98 twist.

Some other interesting twist rates:
577 Nitro Express 1 in 30
500 / 465 Nitro Express 1 in 30
505 Gibbs 1 in 15.98
475 #2 Jeffery 1 in 18
470 Nitro Express 1 in 20.98
450 Nitro Express 1 in 15
458 Winchester 1 in 14
404 Jeffery 1 in 16.54
416 Weatherby 1 in 14
416 Remington 1 in 14
9.3 by 64 1 in 14.17

Take care,
Dave