Gunsmithing Bullet tumbling

[Smokin7s]

I had a friend at a law enforcement agency call me this week wondering about bullets tumbling really bad in a lot of ammo they’d purchased several thousand rounds of for practice ammo. He said they were tumbling at really close distance and the tac guys were getting light baffle strikes. I’m no expert but, figured I could rule out a few things and figure it out and I’m stumped. They’re 62 grain 5.56 cartridges being shot out of rifles that regularly shoot that bullet weight they are 1:7 and 1:8 twist rifles and the bullets showed similar results across multiple rifles a few larue and other high end rifles. They paper tested them and they’re fully keyholing at 7 yards. The guys shooting aren’t dummies by any means. I assumed the bullets were undersized but they’re measuring an average of .2253 (can slightly oversized cause tumbling?) the boat tails are scuffed terrible but I imagine that’s par for mass produced factory fmj. I milled 10 of the bullets in half and everything on the inside appears evenly filled and normal from what I have seen. I don’t have any pride here I’d just like to help these guys out since they’ve purchased a boat load of this stuff, and probably are going to need some reasoning when they send it back or attempt to.

 

[carbonbased]

Seven yards? Wtf!!!

Wait. Maybe that’s a good thing lol. Getting hit at close range with a sideways 5.56 tumbler would eff you up.

 

[Smokin7s]

Seven yards? Wtf!!!

Wait. Maybe that’s a good thing lol. Getting hit at close range with a sideways 5.56 tumbler would eff you up.

Yeah I’d understand it at a little distance but 7 yard tumbling is nuts

 

[Modoc]

Thinking of some of the things I have encountered:

Bullet velocity appropriate? I had 221 FB with a subsonic load print 55s sideways at 25 yards

This is multiple rifles? To rule out badly eroded barrel

Jackets damaged on the bullets? Overcrimped?

 

[Smokin7s]

Thinking of some of the things I have encountered:

Bullet velocity appropriate? I had 221 FB with a subsonic load print 55s sideways at 25 yards

This is multiple rifles? To rule out badly eroded barrel

Jackets damaged on the bullets? Overcrimped?

The crimped portion of the jacket isn’t terribly deformed the base of the boat tail is torn up.

 

[6.5SH]

Barrels been checked out with a bore scope yet?

 

[Smokin7s]

Barrels been checked out with a bore scope yet?

We decided to start with bullet since every other weight and brand of ammo was working good. By several barrels I mean 10 or so all showing the same results or similar with just this one ammo.

 

[hlee]

The crimped portion of the jacket isn’t terribly deformed the base of the boat tail is torn up.

Define "torn up." I've read somewhere that the boat tail is more important to stability than the tip.

 

[Wannashootit]

Define "torn up." I've read somewhere that the boat tail is more important to stability than the tip.

This is logical...
Pic of a pulled boolit would be helpful. Never encountered it, because I've never shot fucked-up bullets- but if they're really that bad, it's reasonable that the combustion gases pushing an asymmetrical bullet base could induce imbalance.

My question is who's ammo is this, and bullet? Even pulled bullets and factory "blems" aren't defective to this extent.

probably are going to need some reasoning when they send it back or attempt to.

Send them photos of a half-dozen of the defective bullets. No reasoning needed...

 

[Smokin7s]

I really don’t think the boat tail is torn up enough to be the reason that they are tumbling at the crown we were shooting 1000 yards and they were shooting shitty groups. I would understand. Here are the best pictures I could get.

 

[6.5SH]

I really don’t think the boat tail is torn up enough to be the reason that they are tumbling at the crown we were shooting 1000 yards and they were shooting shitty groups. I would understand. Here are the best pictures I could get.

No idea if is a side effect from the gouging when those were seated or the cause of it; but those look to have an enlarged 'ring' at the end the bourrelet going to the boat tail.

Not hard to imagine these having some wild in-bore tipping effect.

 

[hlee]

Yeah, these bottom 2 ain’t gonna fly for shit…

 

[Im2bent]

Why the forensic work? Since when does the customer have to figure out what's fucked? Contact seller say wtf over. Show keyholed targets at 7 yards. This is a Leo agency, what the supplier won't replace them?

 

[Ledzep]

What does the back end look like?

Only thing I can think of is excessive oil trapped in the bullet causing the jacket to pop (maybe? You'd probably see lead spirals out of them at close range on paper), or an insufficient core seat operation so the cores are loosey goosey. That's pretty wild for a 62gr in a 7-8 twist.

 

[AccuSol-ERN]

Check some of those rounds for concentricity at the neck and just forward of the neck. If the bullets are oversized like you say, I wouldn't be surprised if there is some wobble inducong funkyness going on......the displaced material has to go somewhere.

Also, compare the keyhole to the pulled bullet. Not uncommon for a failed bullet to shed the jacket completely and the core punch the keyhole......especially at lower velocity.

Ern

 

[Jadazu]

Maybe section a couple. It seems unlikely to be the case here, but loose cores (core stripping) will keep a bullet from stabilizing.

ETA: What Ledzep said...

 

[Terry Cross]

Why the forensic work? Since when does the customer have to figure out what's fucked? Contact seller say wtf over. Show keyholed targets at 7 yards. This is a Leo agency, what the supplier won't replace them?

This is what I was going to suggest.

This isn't the OP's worry. Perhaps just for interests sake but it is not for you to figure out when the ammo is going berserk out of multiple known healthy guns.

The agency needs to contact the supplier and have it replaced.
Continuing to worry with it could easily damage one or more of their suppressors and for sure waste what little training time they have each month.

 

[Smokin7s]

Why the forensic work? Since when does the customer have to figure out what's fucked? Contact seller say wtf over. Show keyholed targets at 7 yards. This is a Leo agency, what the supplier won't replace them?

Because they asked and wanted to figure out if they’re gonna be fucked on training ammo for the next however long it takes to replace this ridiculous quantity.

 

[Smokin7s]

This is what I was going to suggest.

This isn't the OP's worry. Perhaps just for interests sake but it is not for you to figure out when the ammo is going berserk out of multiple known healthy guns.

The agency needs to contact the supplier and have it replaced.
Continuing to worry with it could easily damage one or more of their suppressors and for sure waste what little training time they have each month.

They’re going to end up going back. But they asked thinking I would have answers and I really don’t. Outside of being the lowest bid fmj shit and slightly oversized in the ogive nothing to me suggest it coming out totally sideways.

 

[MrSmith]

I'm not as knowledgeable as most of the posters but:

I don't see any rifling engraved on the slugs. There are scratches but nothing that looks like lands and grooves.

That cauliflower on the OD just forward of the boat tail looks like blow-by to me.

Worth what you paid.

Thank you,
MrSmith

(Nevermind, In my best Gilda Radner voice}

 

[hlee]

I'm not as knowledgeable as most of the posters but:

I don't see any rifling engraved on the slugs. There are scratches but nothing that looks like lands and grooves.

That cauliflower on the OD just forward of the boat tail looks like blow-by to me.

Worth what you paid.

Thank you,
MrSmith

Bullets we’re pulled, not shot.

 

[Gemsbok]

Would a powder shortage for low MV cause that?
@Modoc suggested subs...

 

[Terry Cross]

Would a powder shortage for low MV cause that?
@Modoc suggested subs...

Anything in that realm of issues would quickly rear it's head with obvious function problems (not having enough energy to gas the system) and the report would be noticeably muted.

I don't think it is velocity related.

 

[Aftermath]

If a bullet leaves the case and enters the bore at a yaw...