I found an online claim that a 55 grain 5.56 in a 1/7 twist barrel may fly apart, and that you need to go with a heavier round for that level of stabilization/twist. They also say 55 grain won't be accurate with this twist.

This all seems like nonsense to me. But I trust those on SF to put me straight on this one. Thoughts?

Most of the available 5.56m ammunition is 55 grain, and most of the AR-15s out there are 16" barrels with a 1:7 twist, so, it's nonsense.

55 grain 5.56\223 has no issues out of a 1\7 barrel except it will shoot to a different point of aim than the 62 grain rounds.

I've heard credible stories of 40 grain projectiles disintegrating in flight when fired out of a 220 Swift, but we're talking about thin-jacketed varmint bullets leaving the muzzle at around 4200 fps.

I've heard the same thing about the lighter .223 rounds. From what I've read it's been traced to the thinner jackets that varmint bullets use to help prevent overpenetration.

quote:

Originally posted by parabellum:
I've heard credible stories of 40 grain projectiles disintegrating in flight when fired out of a 220 Swift, but we're talking about thin-jacketed varmint bullets leaving the muzzle at around 4200 fps.

As parabellum mentioned, some bullets at some velocities have disintegrated in flight. I believe the phenomenon has even been seen by member(s) here.

To say, though, that a 55 grain bullet at any 223/5.56 factory loaded velocity will disintegrate like that demonstrates an amazing degree of ignorance about the subject. Vast numbers of rifles with 1/7 inch rifling twist rates have fired vast numbers of 55 grain bullets without the claimed effect having been reported.

As for a particular twist rate’s effect on precision/accuracy, a rate that’s faster than required for bullet stabilization is sometimes referred to as the bullet’s being “over stabilized.” That’s a meaningless term, but according to the ballistician Bryan Litz, a faster than required twist rate can affect precision. That’s because the faster the bullet rotates, the greater the effect of any imperfections in the bullet. He says that’s why benchrest shooters who strive for maximum precision at relatively short distances to the exclusion of other considerations usually use flat-based bullets that can be stabilized in slower twist barrels.

For most shooters, though, such issues don’t matters because other factors are of greater practical concern. To cite my own experience, I usually shoot my Tikka rifle chambered for 223 Remington with two types of ammunition, IMI 77 grain Hollow Point Boattail Match or Frontier 55 grain Hollow Point Match. The barrel has a 1/8" rifling twist rate, so slightly slower than 1/7, but not much. Guess which load, the 77 or 55 grain, gives me more precise results. Yes, the Frontier 55 grain even though it would be stabilized with a much slower twist rate, 1/12 or even 1/14".

quote:

Originally posted by r0gue:
I found an online claim that a 55 grain 5.56 in a 1/7 twist barrel may fly apart...

Can you provide the source? I call this a serious case of BS.

I have personally witnessed Hornady 7mm HPBT match bullets pushed to an MV well north of 3,000 fps in a fast-twist barrel disintegrate into a puff of grey dust. This was at an ELR match in Wyoming, where the shooter was wildcatting a large case into a too-small bore.

A buddy witnessed a over-bore wildcat load with a fast-twist barrel, where the thin-skinned 40 grain varmint bullet disintegrated shortly after exiting the barrel. The modern equivalent is likely a 22 Creedmoor.

Both of these problems occurred when a bullet with a really thin copper jacket is pushed beyond its design specs -- the bullets weren't designed to spin at such high RPMs. The 55 grain FMJ bullet is really quite sturdy, with a fairly thick copper jacket. It might have issues if wildcatted from a necked-down 50 BMG case, but it handles a 1/7 twist 5.56/.223 load just fine.

It was just a Google search and some posts on Quora, Reddit etc. It wasn't consensus by any means, but I saw one or three posts mentioning the possibility. The velocity note above makes the most sense. I'm going to stick with 55 grain.

quote:

Originally posted by r0gue:
...some posts on Quora, Reddit etc....

Not good sources for firearms information.

quote:

Originally posted by r0gue:
I'm going to stick with 55 grain.

55 FMJ has tumbling and fragmenting characteristics which can be very good for HD purposes. It is inherently lacks good accuracy. It is the least expensive bullet to manufacture.

There are heavier bullets which offer better penetration, better expansion, better accuracy, better flight ballistics. But they cost more than 55 FMJ.

It can be a thing, though no personal experience. The setup is ‘super explosive’, thinly jacketed bullets, faster rifling, pushed fast.

My being a prairie dogger, varmint bullets are a thing. Hornady made/makes thin jacket bullets that have a caution of excessive speeds, 3500 as I remember.

The setup could be, pushed fast in a 22-250, then with a faster than customary 1/14” rifling.

Shooting M-16A1 rifles with the 1\12 barrel we got about 1.5 MOA accuracy out to 3OO yards. After that accuracy dropped off.

quote:

Originally posted by fritz:
55 FMJ has tumbling and fragmenting characteristics which can be very good for HD purposes. It is inherently lacks good accuracy. It is the least expensive bullet to manufacture.

There are heavier bullets which offer better penetration, better expansion, better accuracy, better flight ballistics. But they cost more than 55 FMJ.

quote:

Originally posted by fritz:

quote:

Originally posted by r0gue:
...some posts on Quora, Reddit etc....

Not good sources for firearms information.

Hence my checking in here before assuming it is correct.

I have a 6.5 twist .223 meant for 90 gr VLDs which it shoots well.
It will, however, deform a 90 gr SMK and disintegrate a 75 gr Hornady in flight at top velocity. Reduce a bit and they shoot accurately.


I would not worry about a common 55gr FMJ in whatever barrel. The Army tested to be sure they could shoot old stock ammo in new barrels.

A thin jacketed bullet at excessive velocity flying apart I would think would be a hollow point that meets too much air resistance. Is anyone thinking that it flys apart due to centrifugal force from the rapid rotation?

quote:

Originally posted by honestlou:
Is anyone thinking that it flys apart due to centrifugal force from the rapid rotation?

That is the usual explanation.

The lead core of most bullets is relatively soft and easily deformed, i.e., will come apart if not held together by the jacket when rotating fast enough. The bullets that are most associated with the disintegration phenomenon are those intended for use on small “varmint” animals and usually have thinner jackets that provide less structural integrity. There is also some indication that the characteristics of the barrel rifling can affect what happens to a bullet. If the lands and grooves are deeper or the rifling is rough, that may weaken the bullet jacket.

It’s sometimes surprising to realize that a bullet fired at 3000 feet per second velocity from a barrel with 1/7 inch rifling twist rotates at over 300,000 revolutions per minute.

There is the theory that high velocity and high spin is melting the lead core, causing bullets to disintegrate or "comet tail" on target. Some Newton bullets had a layer of paper between jacket and core to insulate the core from barrel friction.

I've bever seen 55 grain bullets shed their jackets regardless of twist rate.

quote:

Originally posted by Jim Watson:
There is the theory that high velocity and high spin is melting the lead core, causing bullets to disintegrate or "comet tail" on target. Some Newton bullets had a layer of paper between jacket and core to insulate the core from barrel friction.

I don’t know what causes lead to sometimes be extruded from bullets, but it doesn’t require high velocities and fast twist rates.

The large gray circle about in the middle of the picture and the small gray swirls leading into some of the central bullet holes are lead deposits. Ammunition was 9mm Luger Blazer Brass fired from a pistol. The small angular holes like the one near the bottom center of the photo were made by pieces of the jacket shed from the bullets.

Although pictured is an extreme example, when my agency was using 9mm Blazer ammunition, I saw the phenomenon regularly from close distance shots.
(We switched from the Blazer to Speer Lawman ammo.)

I'm guessing the Blazer rounds were open base bullets. I'm not sure of if the Lawman is a sealed base, but it is better quality ammo than Blazer.

quote:

Originally posted by sigfreund:
I don’t know what causes lead to sometimes be extruded from bullets, but it doesn’t require high velocities and fast twist rates.

The large gray circle about in the middle of the picture and the small gray swirls leading into some of the central bullet holes are lead deposits. Ammunition was 9mm Luger Blazer Brass fired from a pistol. The small angular holes like the one near the bottom center of the photo were made by pieces of the jacket shed from the bullets.

Although pictured is an extreme example, when my agency was using 9mm Blazer ammunition, I saw the phenomenon regularly from close distance shots.
(We switched from the Blazer to Speer Lawman ammo.)

This message has been edited. Last edited by: SgtGold,

quote:

Originally posted by SgtGold:
it is better quality ammo than Blazer.

Yes. When I contacted Speer about what I was seeing, the rep basically said, “Yeah, we know. Use Lawman ammunition. Can I send you a couple of cases?” “Yeah, sure!”

Unfortunately we never got any. There was no reason why they needed to give us free ammo, but ....

This message has been edited. Last edited by: sigfreund,