140 A-MAX fails in flight to target @ 2950 fps

[elkaholic]

Michael.....I have shot a bunch of 140's through my 3 groove/8 twist lilja over the years in my 6.5 Sherman at 3150'. Most of these at 2500' elevation with temps as high as 90+ degrees. I have never yet had a failure and a 3 groover is no doubt harder on bullets. I have around 1800 rounds through this barrel and it is getting rough in the first few inches of bore. I would lean toward the lot of bullets or something in your particular rifle? I have fired a few at 3200' with no problems. It seems unlikely to me that the "normal run" of 140 amax is the problem......Rich

 

[Michael Courtney]

Michael.....I have shot a bunch of 140's through my 3 groove/8 twist lilja over the years in my 6.5 Sherman at 3150'. Most of these at 2500' elevation with temps as high as 90+ degrees. I have never yet had a failure and a 3 groover is no doubt harder on bullets. I have around 1800 rounds through this barrel and it is getting rough in the first few inches of bore. I would lean toward the lot of bullets or something in your particular rifle? I have fired a few at 3200' with no problems. It seems unlikely to me that the "normal run" of 140 amax is the problem......Rich

It's hard to pin a definitive cause on phenomena that only occur in a minority of rifles.

It will be telling if Hornady asks for the lot number or if I have any bullets left to send.

 

[elkaholic]

Yes it will.

 

[Catfur]

Berger went to increasing the thickness on their match bullets because of in-flight failure during match conditions, where long strings caused intense barrel heat. The hot barrel would transfer enough heat to the lead core to cause it to melt, and the jacket can't contain the liquid (with no structural integrity of it's own). Since the bullet failures occurred in the hottest part of the match, towards the end of a string, this may be the cause.

 

[Michael Courtney]

Berger went to increasing the thickness on their match bullets because of in-flight failure during match conditions, where long strings caused intense barrel heat. The hot barrel would transfer enough heat to the lead core to cause it to melt, and the jacket can't contain the liquid (with no structural integrity of it's own). Since the bullet failures occurred in the hottest part of the match, towards the end of a string, this may be the cause.

Given that it is the only theory with such compelling supporting data (though in a different bullet design), I'd have to say this idea is a leading contender at this point.

However, this theory says very little about why we never saw the problem shooting hundreds of bullets and numerous matches in Colorado. Yes, it was usually 15 degrees or more cooler in Colorado, but is that difference in ambient temperature really enough? Maybe, but gotta keep an open mind about other causes.

 

[Catfur]

I can't say, just throwing that out there. But 15 degrees may be the difference between solid, and partially melted lead.

 

[elkaholic]

Berger went to increasing the thickness on their match bullets because of in-flight failure during match conditions, where long strings caused intense barrel heat. The hot barrel would transfer enough heat to the lead core to cause it to melt, and the jacket can't contain the liquid (with no structural integrity of it's own). Since the bullet failures occurred in the hottest part of the match, towards the end of a string, this may be the cause.

I think this is PARTIALLY true. The heating of the barrel would cause more friction which would increase the temp of the bullet traveling down the bore but if the barrel was so hot as to melt the core in the chamber, you would have far worse problems than just bullet failure (IMO) ......rich

 

[Barrelnut]

Berger went to increasing the thickness on their match bullets because of in-flight failure during match conditions, where long strings caused intense barrel heat. The hot barrel would transfer enough heat to the lead core to cause it to melt, and the jacket can't contain the liquid (with no structural integrity of it's own). Since the bullet failures occurred in the hottest part of the match, towards the end of a string, this may be the cause.

This is what I was alluding to in my first reply. This is the reasoning for the hunter verses target Berger bullets.

Another thought. On the hot day with hot rifle in the last ten shots of F-Class, when you chamber the next round may add to the chances of a failure. By the time the target is pulled, scored and raised again, is about one minute. If the round is loaded as the target is initially pulled for scoring, it can set in the hot chamber for about a minute. This obviously gives the bullet more time to warm up. Who knows that minute could be the tipping point. I always chamber my round after acquiring the new target and shoot in about 10 seconds.

You would think that other A-Max shooters would have encountered the issue at some point at various events at that range.

 

[Michael Courtney]

This is what I was alluding to in my first reply. This is the reasoning for the hunter verses target Berger bullets.

Another thought. On the hot day with hot rifle in the last ten shots of F-Class, when you chamber the next round may add to the chances of a failure. By the time the target is pulled, scored and raised again, is about one minute. If the round is loaded as the target is initially pulled for scoring, it can set in the hot chamber for about a minute. This obviously gives the bullet more time to warm up. Who knows that minute could be the tipping point. I always chamber my round after acquiring the new target and shoot in about 10 seconds.

You would think that other A-Max shooters would have encountered the issue at some point at various events at that range.

They have, and one of the other shooters discussed it with my daughter. Most of the other shooters at that range have moved away from A-MAX bullets because of the trend to lose bullets in flight. No other shooters were shooting it that day.

My daughter waits to load the new round until she has assessed the previous hit location and is within a few seconds of shooting. The main motive was to reduce vertical stringing from the round cooking in the chamber, but it prevents the bullet from warming in the barrel also.

 

[Michael Courtney]

I can't say, just throwing that out there. But 15 degrees may be the difference between solid, and partially melted lead.

Agreed. At some point in adding more heat, you start to melt the lead.

 

[varmintH8R]

I am pretty sure (but not positive) the tips on the A-Max are made of Acetal. Acetal has a melt point of about 335F. It is also a semi-crystalline plastic, meaning it will begin to lose stiffness well below that melt point (roughly 220F heat-deflection under moderate load). Your hypothesis about the tips contributing to the failures may have merit - also consider that the metals surrounding these tips are picking up and conducting heat as the day goes on (ambient temps rising, barrel temps rising). This is effectively "pre-heating" the tips over time.

As stated in earlier posts, starting at a higher temp (even just 15 or 20 degrees) can make a huge difference in getting a material into "the red zone". Flight time of that bullet is pretty short, so the heat created by friction "soaking in" to the part has to happen quickly. Starting with a "pre-heated" tip will make a dramatic difference. Heat resistance of plastics is a function of both temperature and time (and how much mass there is to heat up).

The melt temp of lead (according to Wikipedia, I'm not a metals guy) is stated to be 621F.... I would expect an Acetal tip failure way in advance of melted lead.

Pure conjecture as to whether it contributes to the the actual failure method, but rooted in materials science

Brandon

 

[marshal]

What is the temp of a bullet as it exits the muzzle? I'm really curious about the melting theory,
if you pass a bullet held in pliers through an acetylene flame it would take a few seconds for anything to happen, by comparison that's a looong time.
We all tend to think it's the jackets fault, no one thinks about the consequences of inclusions in the core.

 

[Michael Courtney]

What is the temp of a bullet as it exits the muzzle? I'm really curious about the melting theory,
if you pass a bullet held in pliers through an acetylene flame it would take a few seconds for anything to happen, by comparison that's a looong time.
We all tend to think it's the jackets fault, no one thinks about the consequences of inclusions in the core.

When it exits the muzzle, the bullet does not have a uniform temperature, but the places where the lands were in contact are hotter than the rest, a lot hotter.

There is several hundred foot pounds of work done by friction between the bore and the bullet as the bullet is pushed through. This work done by friction heats both the bullet and the bore. One needs to estimate the division of the heating between the bore and the bullet, but a 50/50 split would not be unreasonable.

So, suppose there is 400 ft lbs of work done by friction, half of which (200 ft lbs) heats the copper jacket along the bearing surface, and which tends to be focused where the lands engage the jacket. It's a simple physics problem (if you know the thickness of the jacket and other dimensions along with the heat capacity of the jacket) to estimate the temperature change to the jacket.

Berger paid an MIT modeling group to do all this more precisely, and they determined that the jacket and the underlying lead can be heated above the melting point of lead under certain conditions. These computations suggested that making the jacket thicker would solve the problem, because the thicker jacket would reduce the amount of heating reaching the lead. In an experiment with thicker jackets, Berger observed that the problem was solved with the thicker jackets but could be reproduced with the thinner jackets in certain rifles.

Now, this was a great experiment and elegant approach to solving the problem Berger was seeing in their bullets. But it does not eliminate the possibility of inclusions or melting plastic tips being the culprit in some cases. However, being that the predictions of the calculations were confirmed in careful experiments, Berger's work raises the melting lead idea to the realm of a tested theory; whereas, the melting plastic tip and inclusion ideas are untested hypotheses.

 

[Deleted member 46119]

These posts go the same direction I was thinking about on a long drive.

I HBn coat my bullets. Lower friction.