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Brass troubles

 
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  #1  
Old 07-27-2008, 07:24 AM
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Brass troubles

I was at the range today testing out the new 180gr E-tip bullet and a box of 180gr Hornady interlock when I ran into an interesting problem.

I was using brand new brass and the rifle is my 300wby mag in MKV accumark.
The first loads of E-tips there was no problems at all no preasure signs easy bolt lift the whole shebang. But when i fired the exact same powder charge with the interlocks i was getting powder burns down the side of the case all the way to the head and still no preasure signs.

Then on the 4th shot in the group i extracted the case and found that it had caved in on 1 side of the shoulder. :( I just dont undrstand how this could happen.




I understand that gas is escaping around the side of the case but how, is it because of the canalure?
Any help or sugestion to what may have caused it would be awsome.

Andrew
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  #2  
Old 07-27-2008, 08:35 AM
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Such dents are caused by gas running back down the chamber when firing loads too low in pressure to expand the case enough to form a seal.
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Old 07-27-2008, 01:07 PM
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JAWZ ........

That's one of the worst cases of "delayed detonation" I've ever seen, and it can be dangerous. This happens when your powder doesn't ignite properly. It's caused by a weak primer or a deteriorated powder. As the powder ignites it burns partially, then the blast re-ignites the rest of the powder - after it's half way down the barrel. That creates rearward pressure as it tries to escape around the outside of your case. Let the ammo manufacturer know, and they'll gladly send you a new box. (At least their lawyers will.)

(This is one good reason to use magnum primers whenever using a large amount of powder in huge case.)

- Innovative
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Old 11-23-2008, 04:47 AM
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Re: Brass troubles

boomtube is right on the money, that is caused by too little pressure, not delayed ignition or hang fire.
The reason it has happened is because you changed components without working up the load again, the same would happen if you went from a Barnes to an Interlok also. The all copper bullets develop higher pressures with less powder than most conventional jacketed bullets, therefore you need to add more powder to get the same pressure value.
Whenever you change components you need to start again with about a 5% reduction from the max load and work back up to the previous load, same for changing powder lots.

THIS IS VERY DANGEROUS! you could have ended up with a destroyed rifle, it is known as S.E.E. (Secondary Explosion Effect).
MagnumManiac.
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  #5  
Old 11-23-2008, 11:22 AM
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Re: Brass troubles

MagnumManiac ........

I agree. It's definitely not a hangfire or a delayed ignition. However, "delayed detonation" happens when a full powder charge doesn't ignite properly. As the primer fires, SOME of the powder detonates and pressure builds inside the case. As the powder burns, if flows forward and some of it doesn't ignite (for about nanosecond). During this delay the chamber pressure is slightly reduced. When the rest of the powder reignites in the barrel, the pressure spikes upward again and blows back towards the case (that is no longer completely sealed). The whole chamber is then resealed from the secondary explosion, but not before blowing back between the case and the chamber wall.

(This could also be a good sign to use magnum primers if not already using them. You could also switch to a powder that is easier to ignite.)

- Innovative
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  #6  
Old 11-23-2008, 12:48 PM
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Re: Brass troubles

That dent is also a classic sign of a case head separation




in which the gas is also transversing from the neck area to the case body area. In the above pics and case head separations it would be that the gas is going out the separation and going forward to escape out the bore. Without a blown primer or a separation my guess would be that it is going from the bore/neck area towards the case body and case head.

Interesting.
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  #7  
Old 11-23-2008, 01:33 PM
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Re: Brass troubles

woods .....

Actually, even though both symptoms occurred for you at the same time . . . . they are totally unrelated. Headspace separation is caused by your cases being stretched too far (after pushing the case shoulder too far back when resizing). Firing the case blows it back to fill your chamber, and that can easily rip your case in half.

- Innovative
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