1/ 16"twist : What bullet weights will work?

[Buckshot Willy]

Hello folks.
I am planning on having an AR 15 upper build in .450 Bushmaster.
Since 1/24 twist barrels are only available from the US or from Lothar Walter (special order, minimum number to buy 20 pieces) I am looking into the 1/16 twist barrels.
I'm thinking on using bullets ranging from 250 grains to 400 grains. (.458 resized in a LEE bulletsizing die).
Any info would help.

Thank you.

Buckshot Willy
The Netherlands

[pitted bore]

Buckshot Willy-
It looks like the experts are sleeping or on vacation, so I'll make an attempt at answering your question. If I write an incorrect answer, perhaps the experts will reply and you and I will both become educated.

Several factors determine whether a particular rate of twist will stabilize a bullet. These include the bullet diameter, length, and weight. A plastic tip may change stability too. Velocity is a very important factor in determining stability; the greater the velocity of a particular bullet from a particular twist, the faster the bullet will spin and so the stability will be greater.

With a 1-turn-in-16-inch twist, almost any conceivable .451 or .452 bullet will be stable at any realistic velocity. In general, longer bullets require a faster rate of twist compared with shorter bullets with the same diameter.

Let's use an extreme example to find whether a 1-turn-in-16-inch twist can stabilize a very long, heavy bullet. The Hornady .458 soft point round nose bullet is 1.365 inches long. If you resize it to 0.452 inches in diameter for use in the 450 Bushmaster, it will become about 1.400 inches long. I don't know what the muzzle velocity of this 500-grain bullet might be from a 450Bushmaster, but let's assume a rather low muzzle velocity of 800 feet-per-second. The bullet will be stable at this velocity from your barrel with a 1-in-16-inch rate of twist.

All bullets lighter and shorter than this example will also be stable with this rate of twist.

It's possible that very light, very short .452 bullets with a high muzzle velocity might be "overstabilized". With an unbalanced bullet, too much spin can produce in-flight wobble, which can decrease accuracy. With good quality bullets, this is usually an insignificant problem.

My Springfield bolt rifle described elsewhere on this forum has a 1-turn-in-16-inch rate of twist for its barrel. I have found no problems with accuracy that are caused by the twist rate of the barrel.

If you want to explore stability, the website of JBM Ballistics has a helpful interactive calculator for bullet stability that includes rate of twist as a factor. You can use different bullet lengths, calibers, weights, etc. to find whether your bullets are stable for a particular rate of twist and muzzle velocity: Link to JBM.

Good luck with your project.

--Bob

[Buckshot Willy]

Thanks so far Bob.
I still was in doubt between the 458 SOCOM, but now I am convinced.
The versatillity makes this caliber a champ to me.
But tell me.
How do you resize the .458 bulletts?

[pitted bore]

But tell me.
How do you resize the .458 bulletts?

Buckshot Willy-

It may be best to read about this topic from some forum exchanges in the past:

• Bullet Resizing Question??
  .
• .452 Bullet Sizing
  .
• 325 gr. (.458 to .452) reloading experiment

Sizing a 458 bullet to a 452 diameter is often done with a Lee bullet sizing tool.

Good luck.
--=Bob

[Hoot]

There is no animal on this continent that I would hesitate to take on, even in a rapidly deteriorating situation, with a repeating .30-06. The 200, 225 and 250gr bullets in our 450b trounce the .30-06 for TKO factor hands down. Why on earth this ongoing obsession with a bigger johnson? The lighter bullets are more pleasant to shoot and you can recover quicker for a followup shot, should it be needed.

Rock-on guys...

Hoot

[Buckshot Willy]

In the Netherlands we are only allowed to own 5 guns for sportshooting and hunting regulations are quite strict.
Conversion kits are not limited.
A 30-06 would take a place on my license where a 450B conversion upper does not.

[Hoot]

In the Netherlands we are only allowed to own 5 guns for sportshooting and hunting regulations are quite strict.
Conversion kits are not limited.
A 30-06 would take a place on my license where a 450B conversion upper does not.

Oh, I get that Willy. That's why I totally understand the appeal of the AR platform. One registered lower and as many caliber uppers as your mission requires and your wallet can tolerate.

Hoot

[Buckshot Willy]

Indeed.
For a hunting license here I would need permission of some landowner.
Hunting is more and more elite only.
I'm jealous on you guys.
You would need to follow an aditional very expensive hunting course here.
I would be allowed another 6 aditional guns but for some brief periods of hunting it would cost me big money.
Way too much for the few times I am planning to do this.

[wildcatter]

Buckshot,

Pitted Bore and Hoot have it down pat and you'd do well to heed their advice.

The lighter bullets such as 230gr will of course stabilize, but will over Rotate (RPM's will be excessive) and will try to fly apart, because of excessive Centrifugal Forces. All though, Pitted Bore has not seen this effect, with his Bolt-Gun and 16t barrel, at Maga-Speeds, but I and others have. It might be that the barrels I have seen it in, has way to aggressive rifling in it, or... Long answer, but the faster twist do favor the heavier bullets, but GREAT work can be had with the lighter bullets and a 16t Barrel.

But, if I were to buy just one barrel and the choices were a 16t and a 16t, then I would feel fine with a 16-twist barrel and just deal with the rotational forces. Remember, the faster the speeds the higher the centrifugal forces, so use a quality bullet and keep the speed down. Find the speed wherein the groups go to heck and back off from there (3 MOA +-). But as Hoot suggest.." I would never feel out-gunned with a 230gr FMJ at 2000fps" (and your speeds should be in the 2200fps++ area), Hunting Anything period, and I worked as a PH in Alaska for years. Polar Bears, Moose, etc., will all EASILY SUCCUMB to the FMJ at these speeds and they won't expand. For anything in the big game category, it might be advisable to stay away from the Hollow-Pointed Bullets, for fear of over-expansion and under penetration. Unless of course that HP was designed for our speeds, like in a 460-S&W or 454 Casull. Of course who cares about expansion, the .452 bullets are already bigger than a 30cal gets after expansion. So, with a FMJ you get total penetration, with tons of Great Effects, do to Hoots assertions.

My suggestion is, if a 16t Barrel is pretty much your limitation and Match Accuracy is not a Terribly Huge Factor, but reasonable accuracy is, then a 16t is just fine. If you were only ever going to shoot light for caliber bullets, then a whole different twist is in the making. But as I understand it you really want to use a 16t Barrel, right?

A 230gr FMJ using lil-gun powder. Run the bullet at moderate to slow speeds first and check your group size as a Standard to work against. then as you "SAFELY" increase speeds and you'll eventually start to see, say three MOA, "SAFELY" increase speeds until you see, say Five MOA (This is all just an example of a work-up routine and the "SAFETY" Factor you will use, will dictate what you actually do and how you actually achieve your desired results.). If this is done "SAFELY" you can back off to the group size you need. Remembering, three MOA is Nine-inches (9") at 300yds, and WELL more than enough accuracy for anything you will kill in Alaska (Adult Deer are 18MOA, Caribou/Moose are 24MOA, Adult Polar bears are 30+ MOA etc.).

This is where you have to decide, do I want a Match-Gun or do I want a Killer-Gun? What is the Mission? You can almost have both, or at least have an exceptable Trade-Off. But without and Mission Definition it will be difficult to achieve.

I hope this clears some of the Cob-Webs out of your thinking and helps your decisions.



..t