Home Forums Hunting & Shooting Ask The Gunwriters Bullet RPM Causing Bullet Failure

I don’t know why this is surprising to me but my 1-7” twist, 20” FN AR-15 is causing 55 gr. Speer SP bullets to come apart shortly after takeoff. Load is 27.5 CFE223 at 3200.



I have shot a number of 55’s in my 1-7” and this is the only bullet that has done this. I thought it could be a feeding issue deforming the tips but feeding them single does the same thing.

Went and collected a little data to bring to Speer with what is going on with the 55 gr SP out of my 1-7”, 20” FN AR15. I’m curious what their findings are.

Fired the first 5 shots at 5 yards. Everything looked normal.

Fired the next 5 at 10 yards. One looked normal, you can see the lead starting to separate and swirl out of the bullet. This is not powder residue.

Fired 5 more at 15 yards. There are small lead swirls. Not sure why it’s less dramatic than the 10 yard shots.

Fired 10 shots shots at 25 yards, aiming at the bottom left bull because I couldn’t see where they were going. 2 of them looked okay though not accurate, 4 of them hit sideways and I believe this is just jackets with no lead inside though it’s hard to say for sure.

Walked back up to 15 yards and shot 5 more. 2 looked okay, 3 had major separation. Not sure why the differences but maybe barrel heat has something to do with it.



Here is a sectioned comparison. I only had a small 1/8” end mill so these have a lot of tooling marks but it’s easy to see the jacket on the Nosler Varmigedon is almost twice as thick.



These bullets and this load shoots great in my XBolt 1-9” .223.

Very weird findings and a good example of why you don’t want to make too many rounds for a gun without testing them.

Question, Are there other bullets you’ve seen do this out of fast twists?

Thanks,

Todd

If it could be brought under control it might make a great long-range waterfowl load.

Have seen that several times over the years. It's more common on fast-twist barrels, but also occurs in "normal twist" barrels when shooting prairie dogs in hotter weather.

220 swift with light bullets. This was back when the twist was in the range 1X12.. All you would see was a puff of grey/black down range.

Shooting bullets in a 22-250 that were designed for 222- I used to see puff/cloud of lead 20 feet in front of the muzzle. I may have changed the loads or bullets or??? But I have not seen it as much lately.
Some people say that there’s no “down” to fast twist. I’m not in that crowd of believers.

With lighter bullets, I've seen a flap open up on the side of the copper jacket. In an AR, the bullet leaves the muzzle just below the temperature needed to melt the lead core, so molten or near molten lead flies out of the rupture, leaving characteristic curlicues as the bullet enters the target.

I have some 62 grain bullets made by Nosler for the Australian military that did this in my 1:7 M4gery. Nosler was very quick to offer to replace them, but I thought that the shipping was out of proportion to the problem.

Just wondering aloud here........

Could a rough gas port score a bullet jacket enough to cause failure?

I'm pretty ignorant on the subject of gas ports.

Interesting question. One thing we do know, older barrels tend to make the problem worse.

Thank you all for sharing and your input.

I thought the same thing could be happening but I have close to 1500 rounds through the gun with all manner of bullets and this is the only model having this issue. I can’t see any burrs or feel any with the cleaning rod. Also haven’t found any copper shavings in the BCG. All other bullets are fairly accurate, 1.5 MOAish and will shoot the 69 gr match kings very well. I don’t think this is the issue currently but not totally dismissive of it either.

Todd

I was involved in the testing of some of the first 6.5 twist barrels to shoot 90gr JLK's. A few of this group had Krieger cut rifled barrels and a few of us had buttoned barrels from Pac-Nor. (Rost was involved in this effort as well). It seems that the Kriegers were more prone to bullet breakup than were the buttoned barrels. Around that same time, an engineer versed in such things sent me an analysis he had done previously on factors that contribute to bullets going "poof".
From memory, aside from the already named factors of heat, and pressure, he cited bullet engraving (the taller lands of the cut rifled Kriegers) causing stress points in the jackets making them more prone to letting loose. Similarly bore condition could make a barrel more prone to causing "poofs". And while the case with the 90's (Jimmy was swaging down 6mm jackets to 224 back then), thin varmint jackets were more prone to letting loose My sometimes faulty recollection is that one of the Kriegers that was experiencing bullets breaking up had some miles on it and the combo of bore condition and cut rifling were determined by Boots Obermeyer to be the main culprits. If I'm not mistaken, Jeff ended up with one of the Krieger barrels off a bolt gun because the owner wasn't happy with the velocities he was getting. Maybe he'll see this and post.

...revisiting your pics, I see that they're Varmint bullets. That might be your problem. For the heck of it I might consider scrubbing the crap out of a barrel doing that with JB.

A thicker jacket does solve the problem. Berger Bullets was having this problem, and a thicker jacket was a solution.

The Hornady 55 gr SPSX is another bullet prone to coming apart with a little encouragement.

I have seen this many times but normally with a cartridge of larger powder capacity than a 223, First time I had this happen was with a 22-250 1-8" twist 3 groove, but the worst by far was my 6mm-284 1-8" twist 3 groove Pac-Nor barrel.............a Hornady 105 A-Max NEVER made it to target EVER, I tried 105VLD Bergers and they worked for a few hundred rounds before they started blowing up also. most of this barrel's life was with 107gr SMK's (a much tougher bullet).
Problem was solved by switching to 5 and 6 groove barrel's on the next go around.
In the OP's case use a tougher bullet than a speer or hornady

Thin jackets are usually the culprit. I have a 20 practical with an 8 twist barrel that'll spin apart 39 gr sierra blitzkings, 40 gr Hornady VMax's hold together just fine. The VMax has a thicker jacket than the sierra. The sierras shoot great out of my other 20 practical with an 11 twist. As Mule Deer says, heating up a barrel on a prairie dog town will also make them fail more. Some people here like to say that you can't have too much twist, but you can when it gets to that point.

Switching to a bullet with a thicker jacket will usually solve the problem.

Is it too fast of twist or the bullet jacket is too thin?

The 204's might be a different story, but in 22 and 6mm the Hornadys and Speer are the first ones to blow up, I've never had a Sierra of any kind blow up

A combination of the two. Ultimately it's the bullet is too fragile to handle the RPM generated. You can decrease the RPM by less twist or slowing down the bullet. What might be OK in an 8 twist .223 might blow up in an 8 twist 22-250. Some barrels are harder on bullet jackets also. Rough bores tend to tear up jackets and the bullets come apart if pushed. Three groove barrels are notorious for blowing up bullets which tells me they're tough on bullet jackets.

I'm a believer that if it hurts when you do something then don't do it. If your bullets are blowing up then switch bullets. Slowing down the bullets to decrease the RPM isn't really practical. Why buy a 22-250 if you can only shoot it at .223 velocities? When my 20 practical was blowing up sierras I switched to hornadys and it solved the problem. I even called Sierra's tech line and they said the 39 blitzking should hold together with an 8 twist, they were wrong because it doesn't in mine. Twists are faster today because people want to shoot long bullets. They want do it all rifles but that comes at a price of not being able to shoot some of the more fragile bullets. Ultimately the bullet manufacturers should improve their products to where they won't fly apart with a fast twist but not all have done that.

Switching bullets is easier than changing twist.

I don't know, the .20 cal is the only one I've had a consistent problem with blow ups with. I do have an 8 twist 22-250 that I've shot a lot of nosler 55 gr ballistic tips through. I bought 6000 shooter's pro shop blems and a few had visible defects & they blew up, but as a rule the 55 ballistic tips do fine as fast as I can run them. I've shot plenty of 40 gr ballistic tips through that same rifle at over 4000 fps and they've held together fine also.

I haven't shot any speers other than in a 30-30 decades ago.

The 39 gr. sierra blitzking works fantastic in my other 20 practical that's an 11 twist. It's crazy accurate and really does a number on prairie dogs, it's one explosive bullet. You can almost pinch one flat between your fingers though, it's a really soft bullet. I'm not disparaging them, I just twisted my first rifle too fast. In the right setup they're magic on prairie dogs.

I never had a problem with a 6.5 twist barrel toasting a bullet. Shot 52 bthp enough out of it to know they were fine in the AR15 for the short line 200 yards.

I do have a bolt gun barrel but its a full 6 twist and its still on the shelf having never played.

I did poof some bullets, 22 to be exact, once with a 7 Krieger. AR15 20 inch. 64 Berger flat base IIRC. It was before they worked on better jackets.

I'd road with Nez to Beaumont to shoot a regional. Forgot my ammo at home. He had enough of ammo to share the day. But the 64s never made it to the target. I could have won that with a 182 or so standing, which should have been easy for me at that point. But it was no big deal anyway.

We swapped to other bullets for the rest of the match and never lost one again.

Berger changed the jacket and I never had an issue with that bulllet again. Its been years, so maybe it was 62--64. Was a flat base hp match bullet as I recall.