Range Report Bullets blowing up

[JBD56]

I recently re-barreled a shot out 22-250 barrel to a 22BR in an 8 twist Bartlein for p-dog shooting. It has been difficult to find the heavier bullets that I wanted to shoot with the fast twist. I ended up building a load with 64 grain Berger FB varmint bullets and Varget. I never had any problem with the bullets coming apart at the range while developing an accurate load. While out shooting p-dogs, most of the bullets started coming apart once the barrel had a few rounds through it and heated up.

My questions are:
* Are the jackets on the Berger varmint bullets too thin for this velocity (3300) and twist rate?
* Could this be due to a carbon ring buildup?

I had some 69 grain Lapua Scenars with as well and never experienced any of them coming apart.

 

[Advokaten]

Your barrel and it´s twist is tearing the jackets to bits as soon as the barrel is slightly fouled and hot, the scenars are heavier in the jackets and will most likely take more abuse. I have no first hand experience of this however a good friend of mine has a .223 AI 8 twist that he runs hard with similar results.

/CHris

 

[ahhshoot]

Hey you know what.. I don't know if this is related. I noticed the Berger 300 OTM I am shooting out of my 338 LM are very soft. They don't even penetrate the AR500 steel target from 100 yards. I had a 300 Win that put two holes through this same sheet of steel from 100 yards with Hornady Interlock bullets. I also read a bulletin from Berger saying these bullets would deform under acceleration at times. It's a different caliber but maybe their process or materials are what are causing this. Nothing against Berger, I don't run them fast enough for the deformation to occur and I don't need to punch through AR500 steel, I actually kind of like the idea of being able to use the target at closer range. But maybe you won't be able to run them at your desired velocity for similar reasons.

I did notice with my 6.5 CM that the Lapua Scenars seemed extremely tough. They did not seem to expand even when shooting full jugs of water, just penciled right through the water and both sides, so you might have better luck with the Lapua bullets if you don't want to turn the heat down.

 

[Fred_C_Dobbs]

There are several "theoretical" reasons why bullets fail in flight. The only quasi-scientific test I ever have seen on the matter was run by Eric Stecker, who was Walt Berger's hand-picked successor when he retired. There might have been other such tests conducted, but this is the only one I am aware of, and it also happens to have been "published" on the Internet.

Anyway, Stecker's test proved about as conclusively as possible without being performed in a sterile laboratory that too thin a jacket can cause bullets to fail in flight. His recounting of it at Benchrest Central is here.

In a nutshell, they cooked up two different batches of 6.5mm bullets with a substantial difference in jacket thicknesses, then shot them @1000 yards, which would provide plenty of time of flight to fail if they were gonna. 950 rounds total. Each shot was witnessed by two observers. The bullet was only recorded as failed in flight if both observers agreed they had seen it blow up. None of the thick-jacketed bullets failed, but a statistically significant number of the thin-jacketed bullets did fail.

A couple of quotes from Stecker:

...Bullets from every maker can experience failure under the right (or wrong) conditions...

...ALL BULLET MAKERS HAVE BULLETS THAT FAIL AND MOST FAILURES ARE CAUSED BY THE MELTING OF THE CORE....

(that's Stecker shouting, not me)

The fact that Stecker personally ran this test tells me it is a topic he is keenly interested in. So I would suggest you call Berger and let them know what's going on. I'd wager they'll want to know there is a problem with their product, and they'll probably send you a box of better bullets in the deal.

EDIT:
Berger Technical Support
714-441-7202
[email protected]

 

[rg1911]

Hornady 95-gr V-Max were disintegrating about 25 yards from the muzzle of my 6.5-.284 with 1/8 twist. (I can't remember the velocity, but it wasn't a mild load.) Heavier bullets were fine. I haven't tried the V-Max in my new barrel, yet.

Richard

 

[CMH]

Fred_C_Dobbs,

What do you make of the conclusion that thinner jackets had more failures, but then in the quote from Stecker he is talking about melted cores? Thinner jackets lead to melted cores?

 

[Fred_C_Dobbs]

Fred_C_Dobbs,

What do you make of the conclusion that thinner jackets had more failures, but then in the quote from Stecker he is talking about melted cores? Thinner jackets lead to melted cores?

Sorry for the nonsequitir. The 'article' is fairly lengthy, and I was trying not to be.

Stecker states Berger Bullets hired M.I.T. (not kidding) to do thermal modeling, which confirmed that the friction from being driven down the bore (and not the heat of the pursuing cloud of hot/burning gas) will heat a bullet's bearing surface to in excess of the melting temperature of lead (~621°F, versus ~1983°F for copper). The thickness of the copper jacket initially insulates the core, but since copper is so highly thermally conductive, it's just a matter of time before the excess heat migrates across the jacket and reaches the lead. The heat could manage to cross the thin jackets in less time than it took them to reach the berm, which wasn't the case with the thick jacketed bullets.

The bullets would have been spinning ~254,000 RPM, which Stecker states is well within their design limits. He repeatedly uses the term "melts" but he also notes that before the lead would have got hot enough to liquefy, it would have reached a plastic state. Under such severe centripetal force, he allows that the bullet might fail because the (plastic) core starts to deform, which imbalances the entire bullet, which proceeds to tumble and sling itself apart. All before it actually "melts." But the purpose of the test was to learn how to build bullets that didn't fail in flight, not to determine whether the chicken came before the egg, so the distinction, to Stecker, was immaterial. It was enough to have data showing the thickness of the jackets was responsible.

 

[CMH]

Fred,

Excellent response. Thanks!

 

[Frank Green]

Speed is friction which leads to heat etc....as stated.....now increase the twist way faster then what you need and you just compounded the problem. Also any damage to the barrel (that can be different things) can damage the jackets of the bullets. Throat is rougher as the round count goes up and the rougher throat will beat the bullets up more as well. Also bore and groove size, jacket thickness can lead to the rifling cutting thru the bullets jacket which will lead to failures as well. Also the bullets will vary from lot to lot as well. Several years ago I had one lot of 6mm bullets that would blow up randomly in new barrels and used barrels. Got a different lot of bullets done from the same maker and no problem! Tried a different maker and no issues! It was that particular lot of bullets! You can also have more than one set of circumstances causing the problem as well.

Later, Frank
Bartlein Barrels