A short and thinner jacketed bullet hoofing it out there at 252,000 to 324,000 RPM's, I think I'd spin apart too! Lol

quote:

Originally posted by fritz:
55 FMJ has tumbling and fragmenting characteristics which can be very good for HD purposes.

Is this documented somewhere? I keep hearing it, but I've also read that it was due to the slower twist in the old pre-A2 M-16 barrels and that it won't happen with a modern 1:7 or 1:9 barrel. What's the real scoop on this? Inquiring minds concerned about home invasions want to know.

55gr M193 type bullets break apart at the cannelure when passing through different flight media such as air to water, or air to animal tissue. They also come apart quite nicely when going through building materials, which is why 55gr rounds are not ideal when shooting through vehicles.

Twist rate has an effect, but velocity is the real limiting factor. The chart in the link is a good starting point but should not be taken as exact data for fragmentation.

https://www.ammoman.com/blog/b...rel-length-for-5-56/

quote:

Originally posted by Expert308:

quote:

Originally posted by fritz:
55 FMJ has tumbling and fragmenting characteristics which can be very good for HD purposes.

Is this documented somewhere? I keep hearing it, but I've also read that it was due to the slower twist in the old pre-A2 M-16 barrels and that it won't happen with a modern 1:7 or 1:9 barrel. What's the real scoop on this? Inquiring minds concerned about home invasions want to know.

I have seldom seen such behavior from pistol ammo.
I had some off brand plated 9mm that would keyhole, probably some undersize bullets in the box; and have seen others.

Anecdote Alert
At the IDPA Nationals one year they had a BUG side match, guns and ammo provided for a separate entrance fee. S&W M642s and CorBon Practice .38s with plated bullets. With over 200 people sharing two guns for 20 shots each, that is over 2000 rounds per gun in one afternoon with no cleaning. They got hot and dirty. By the time my turn came, I was seeing shards of copper and flakes of lead pepper the targets. Fortunately they were close enough it didn't matter much.
The two best scores won the well used guns as prizes.

I've only seen 55gr FMJ tumble out of an AK pistol. The bullets were undersized junk, sold under the name of Tula, but who knows what it was.
I have pushed 55gr .224 bullets up to 4000fps MV, out of my super deep throated R700 22-250, with fantastic accuracy, 1 in 12" twist though. They were RPM'n though!

quote:

Originally posted by Expert308:
Is this documented somewhere?

I’ve seen many claims that the M193 55 grain FMJ breaks at the cannelure and there have been gelatin medium tests that show it can happen. I’m far from convinced, though, that it happens all the time in flesh, and based on the tests I’ve seen it doesn’t happen when perforating through something like wallboard or lumber. In my own limited tests through windshield glass when fired with a 1/7" twist rate barrel the bullet tumbles, but doesn’t necessarily break up; in fact I saw more breakup with M855 through a windshield than the M193. This shows the hole in witness paper produced by a M193 bullet fired through a pickup windshield. (The multiple angular holes were evidently caused by glass fragments.)





This was of course a sample of just one, but the M855 bullet broke up passing through the windshield:





Also, and again my test was limited, when shooting through the double walls of a pickup bed, the M193 bullets performed better than M855 bullets. That’s not surprising because a longer bullet (the M855’s) fired at the same twist rate is less stable than the shorter 55 grain bullet of the M193.

The reason nonexpanding bullets tumble in flesh is because flesh is much denser than air and the bullet isn’t stabilized sufficiently to remain point forward. Most recently I’ve seen discussion that points out that what happens in flesh is partially dependent upon the degree of yaw of the bullet at the time of impact. If the bullet happens to impact with its point in direct line with the line of flight, it will tend to penetrate farther than if it’s yawing slightly. That’s believed to be the reason that bullets like the M855 cartridge’s behave inconsistently. But as far as I know, if the test medium is deep enough, sooner or later both bullets as well as other FMJ spitzer bullets will tumble.

As an historical note, the Germans were early adopters of spitzer (pointed) bullets in their military rifle cartridges, and although other European forces did as well before World War I, the effect of a tumbling bullet was not well known. The greater wounding effects were occasionally attributed to the belief that the Germans would sometimes “modify” their bullets by filing off the point. Although that may have sometimes been a practice, the round nose bullets in use before spitzer bullets were adopted tended to drill straight through rather than tumbling, and therefore the greater wounding effects of the latter weren’t recognized and were thought to be due to a modification.

In fact, I believe that the wound ballistics effect of unstable, tumbling bullets wasn’t generally recognized until much later. I still remember a conversation with another soldier in 1972 about the subject. He had seen a claim that the M16’s bullets caused significant wounding effects because they tumbled in flesh. He denounced the claim as military propaganda intended to dispute the obvious (to him) fact that the 0.224" diameter bullet of the M193 cartridge was a pathetic performer in combat.

Added:
Sometimes people are confused about what “tumbling” refers to. In this context, it’s what happens when a FMJ spitzer (pointed) bullet hits a fleshy target. It does not refer to a bullet tumbling in flight between the gun and target. Very unstable bullets may tumble in flight, but when they do they become very inaccurate and lose velocity quickly.

A bullet coming apart (fragmenting) inside a target once hit is a different issue than coming apart from centrifugal force on its way to the target and not hitting it.