Bullet failure?? How fast is too fast?

[mike.e]

I use the 142gn Sierra SMK #1742 projectile in my 6.5Gap. It has been very accurate but i have found randomly i am having UNEXPLAINABLE & COMPLETE misses.

This morning I had 4 hits on 1000m target and 2 complete misses. My spotter did not even see "bullet trace" in his spotting scope. He saw this on preceeding 4 shots. First 4 shots formed a 5 inch group. Then the 2 "misses" for want of a better description then next one back in the original group.

I am shooting these projectiles at 3180fps thru a 28 inch Bartlein 1-7.7 twist barrel, and left wondering if i may be experiencing projectile failure.

Does anybody know manufacturers specifications regarding maximum rpm and muzzle velocity these bullets will find acceptable?

 

[David Milisock]

I use the 142gn Sierra SMK #1742 projectile in my 6.5Gap. It has been very accurate but i have found randomly i am having UNEXPLAINABLE & COMPLETE misses.

This morning I had 4 hits on 1000m target and 2 complete misses. My spotter did not even see "bullet trace" in his spotting scope. He saw this on preceeding 4 shots. First 4 shots formed a 5 inch group. Then the 2 "misses" for want of a better description then next one back in the original group.

I am shooting these projectiles at 3180fps thru a 28 inch Bartlein 1-7.7 twist barrel, and left wondering if i may be experiencing projectile failure.

Does anybody know manufacturers specifications regarding maximum rpm and muzzle velocity these bullets will find acceptable?

Your spinning at 4,955 revolutions per second multiplied by 60 is 297,300 revolutions per minute. Sierra should have spin specifications on their site.

 

[Jud96]

I think every bullet and scenario will vary. Today I did some testing with some 66gr Bishop bullets in a .243 Win. I have a Lilja 3G 1-8T barrel and I got up to 3834FPS without blowing up a bullet. This doesn’t mean if I tried a 65gr VMAX or 70gr Sierra that they wouldn’t fail. It’s all bullet, barrel, velocity, and temperature dependent. The general rule of of thumb is anything over 300,000 RPMs is the red zone. You can find this by taking 720 X Speed / Twist. In your case you’re running around 297,000 RPMs. You’re right on the edge of what’s considered the top end for RPMs. But as I said, every scenario is different.

 

[ZenArchery]

Side note: Solid Coppers don’t have a top end.

 

[762plinker]

Side note: Solid Coppers don’t have a top end.

and are not shot in shorter range comp..mainly in real long range2k and more(like king of 2 miles)

 

[243winxb]

Post #9 http://benchrest.com/showthread.php?49336-Berger-bullet-failure-test&

Failures have several causes. The most common is produced by the core melting. The core melts because it gets too hot. The core gets too hot because of the FRICTION between the rifling and bearing surface. This has been proven to be the hottest part of the bullet as it moves through the barrel. This area has been shown in high speed, infared images reaching tempuratures at the melting point of lead.

Other causes for failure are excessive RPM. Since most shooters use factory (bullet or barrel) recommended twist rates failures due to excessive twist rates are rare (but do happen).

Rarer still is a failure caused by extreme barrel issues (damaged bore) extremely poor loading practices (damaged bullet) or extremely poor cleaning practices (which further increases friction).

Another extremely rare cause is related to bullet production issues. Bullet construction that is poor enough to result in bullet failure (and where bullet failure would not have occurred for any other reason) can theoretically occur in situations where standard QA and production procedures are ignored almost completely. I am sure that this is possible but is as unlikely as I can imagine (from all bullet makers).

 

[FeMan]

Other factors to consider are jacket thickness and barrel condition Bullets with thinner jackets will blow up easier/more often than thicker ones. Heat buildup in the barrel can be a big factor Fire cracking also weakens jackets.

I have experienced these failures and seen them many times. The failures I have witnessed invariably start to happen at the end of strings of fire and seem to be more prevalent on barrels with higher round counts. I have not seen 142 SMKs fail but have not run them that hard. No bullet is immune but when I and friends have had the issue, we switched went to Bergers.

 

[dantiff2]

This is very much bullet/ barrel dependent. Be sure you try yourself to see and make sure you don't have on any muzzle attachments (muzzle brakes, suppressors or chronographs). I'm loading 50 gn TNT's to 3360 with a 7 twist and they hold up. That's 340,000+ rpm. Very impressive on critters : ) I doubt your spinning them apart unless you have an abnormally rough bore.
Dan

 

[FeMan]

Although I have never seen it documented anywhere, I also think the caliber matters. For a given rpm, the centrigual force on the jacket increases with diameter and it stands to reason the "safe" rpm will follow suit.

 

[Sandstorm]

How fast is too fast....​

Appears that you have found it...
The last time I saw it was when the barrel heat and spin rate reach a certain point...
like half way through a 20 shot sting in Competition.

 

[6MMsteve]

could be time for a good J&B treatment, then try I don't know what the round count is, 4 gr barrel I'm guessing have you scoped the barrel chkd the crown,

 

[Retired shooter]

I think every bullet and scenario will vary. Today I did some testing with some 66gr Bishop bullets in a .243 Win. I have a Lilja 3G 1-8T barrel and I got up to 3834FPS without blowing up a bullet. This doesn’t mean if I tried a 65gr VMAX or 70gr Sierra that they wouldn’t fail. It’s all bullet, barrel, velocity, and temperature dependent. The general rule of of thumb is anything over 300,000 RPMs is the red zone. You can find this by taking 720 X Speed / Twist. In your case you’re running around 297,000 RPMs. You’re right on the edge of what’s considered the top end for RPMs. But as I said, every scenario is different.

Gentlemen I am from old school math , and dont know the new. Please explain the formula above.
From what I see. the 720 is a constant multipled time the velocity in fps. What is. / .

Thank you.

 

[Murray Brook]

@Retired shooter It is 720 multiplied by the bullet speed in ft/sec divided by the barrel twist.

 

[mongo chicago]

When I over spun a 6.5-06, (I think that was the cartridge) you could see a puff of smoke within about 10 yards.

 

[Retired shooter]

Thank you Murray. That's what I figured, however, I got a significant higher RPM number than jud.
Wanted to verify.

Awesome what can be learned here.!

Thanks guys.

 

[wboggs]

I use the 142gn Sierra SMK #1742 projectile in my 6.5Gap. It has been very accurate but i have found randomly i am having UNEXPLAINABLE & COMPLETE misses.

This morning I had 4 hits on 1000m target and 2 complete misses. My spotter did not even see "bullet trace" in his spotting scope. He saw this on preceeding 4 shots. First 4 shots formed a 5 inch group. Then the 2 "misses" for want of a better description then next one back in the original group.

I am shooting these projectiles at 3180fps thru a 28 inch Bartlein 1-7.7 twist barrel, and left wondering if i may be experiencing projectile failure.

Does anybody know manufacturers specifications regarding maximum rpm and muzzle velocity these bullets will find acceptable?

I've used the 142 smk at 3200 out of a 7.5 tw 5R and never had a failure shooting steel. These are not fast or long shot strings and barrel is very smooth.

 

[wboggs]

I use the 142gn Sierra SMK #1742 projectile in my 6.5Gap. It has been very accurate but i have found randomly i am having UNEXPLAINABLE & COMPLETE misses.

This morning I had 4 hits on 1000m target and 2 complete misses. My spotter did not even see "bullet trace" in his spotting scope. He saw this on preceeding 4 shots. First 4 shots formed a 5 inch group. Then the 2 "misses" for want of a better description then next one back in the original group.

I am shooting these projectiles at 3180fps thru a 28 inch Bartlein 1-7.7 twist barrel, and left wondering if i may be experiencing projectile failure.

Does anybody know manufacturers specifications regarding maximum rpm and muzzle velocity these bullets will find acceptable?

I have another accurate low recoil load using smk 107s at 3305 and have never had a failure. The smk jackets seem to be pretty tough with a calculated 317,280 spin. Again, no fast shooting or long strings.

I use the 142gn Sierra SMK #1742 projectile in my 6.5Gap. It has been very accurate but i have found randomly i am having UNEXPLAINABLE & COMPLETE misses.

This morning I had 4 hits on 1000m target and 2 complete misses. My spotter did not even see "bullet trace" in his spotting scope. He saw this on preceeding 4 shots. First 4 shots formed a 5 inch group. Then the 2 "misses" for want of a better description then next one back in the original group.

I am shooting these projectiles at 3180fps thru a 28 inch Bartlein 1-7.7 twist barrel, and left wondering if i may be experiencing projectile failure.

Does anybody know manufacturers specifications regarding maximum rpm and muzzle velocity these bullets will find acceptable?

 

[jelenko]

FYI. Sierra tech said they recommend keeping 77gr SMK [223] below 250K/260K.
Hornady tech said 280K is max for their 75gr HPBT [223].

As others have already said, the max recommended spin rate varies by bullet.

And, as we all know, exceeding those max's doesn't guarantee the bullet will blow up. It depends on barrel condition.