Pressure Signs...

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Here's another question for the experts...looking for as much exposure as possible:

http://forums.gunbroker.com/topic.asp?TOPIC_ID=409968

I'm trying to get this barrel broke in by Saturday. Thanks!

cussedemgun

ECC,

You describe the indicators of excessive pressure, mainly the flat primers. As this system head spaces on the belt, I doubt head space is causing this problem.

Your problem probably stems from the max 300WM load causing a pressure spike in the larger chamber. It is possible for the bullet to nearly stop while the expanding gasses fill/form the case & then cause a spike as pressure alone broaches the bullet into the rifling.

Use a collet crimp die (any 30 cal. should work) & apply a stout crimp to aq sample of these loads. That should cause enough delay in bullet movement to allow the case to expand first.

Jim

bpost

A belted cartridge that has its shoulder pushed back too far or shot in a too long chamber is excessive head space. It can and will cause head separation, most commonly about 1/4 to 3/8th inch in front of the belt.

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quote:Originally posted by cussedemgun
ECC,

You describe the indicators of excessive pressure, mainly the flat primers. As this system head spaces on the belt, I doubt head space is causing this problem.

Your problem probably stems from the max 300WM load causing a pressure spike in the larger chamber. It is possible for the bullet to nearly stop while the expanding gasses fill/form the case & then cause a spike as pressure alone broaches the bullet into the rifling.

Use a collet crimp die (any 30 cal. should work) & apply a stout crimp to aq sample of these loads. That should cause enough delay in bullet movement to allow the case to expand first.

Jim






So you are saying that the bullet will actually momentarily stop while the pressure blows the case out to the larger chamber, causing a brief pressure spike.?.? This sounds like a logical conclusion...if I'm understanding you correctly.?.?

I seriously doubt it's a head space issue. One of the best 1000 yard gunsmiths in the nation built this rifle. I think it's a combination of old brass, hot loads, and possibly what you are referring to.

I will switch over to all new brass after I shoot these last couple rounds

truthful

If you are getting 6 - 8 heavy reloads from a belted case you are doing well. The belted case is the worst case design ever devised. While intended to strengthen the head of the case, it is the cause of incipient case head separation that you are experiencing. The case must be sized exactly right so that the shoulder seats into the chamber at exactly the same time as the belt. If the shoulder is set back just a touch, the case will stretch and eventually break. If the shoulder is too far forward the round may not chamber.

JustC

Eric, I answered in the RL forum,..but

You are running old brass that was fired in a generous chamber, the resized, and so on and so on. Your shiny ring ahead of the belt is an imminent casehead seperation,..that is a sure sign. Look at a fired one, and that ring will be dark from small amounts of powder escaping during firing. The pressure is contained by the chamber wall,..but only for a time or two. Then it's hot gasses in the face and out the mag well.

also, if you set the shoulders way back for the first firing in your new chamber, then you have likely created excess headspace and during ignition, the primer starts to back out of the primer pocket, and in a millisecond, the pressure blows the case out to the chamber and slams the primer back into the pocket,..creating the flattened look.

cussedemgun

ECC,

Any excess space for pressure expantion will cause problems. It is a well known fact that reduced loads in large capacity cases can cause
just such pressure spikes & have even been known to result in ruptured cases. This is why it is best to fire form with special loads. Use;

New brass
Light bullets
Moderate charge of a faster burning powder
Fiber fill to reduce any excess space
Crimp well


P.O. Ackley said in his "Pocket Manual for Shooters and Reloaders":
"Another blowup which we are quite sure occurs, is when using reduced or semi-reduced charges of slow burning powder in badly overbore capacity cartridges."

The theory is; large capacity case, free space for expantion, magnum primer, & slow burning powder combine to spell disaster.

The primer is powerful enough to move the bullet to engage the rifling. The powder will first pressureize the internal space & the slow burn rate causes a lag for the pressure to continue the push.

Keep in mind this is the accepted theory, I have not yet been able to see inside a case to tell if this the real scoop!

Jim

nononsense

ECC,

I apologize for coming to the party so late but...

Get rid of the old cases and start with new brass and basic, documented loads. This has been dragged out too long and it's not that difficult. Sound reloading procedures and loads will accomplish what you need to get you to the point of developing the loads for the AI case. There is not as much of a significant change in capacity from the standard .300 Win. Mag. case to the AI case. Most of it is strictly in the shoulder angle.

Enjoy your hunt!

Best.




truthful,

"The belted case is the worst case design ever devised. While intended to strengthen the head of the case,..."

Wrong on both counts. The belt is the headspace feature on belted cases. This is a design feature created by the British when developing the .375 Velopex and the .375 H&H slightly later. The belt allows for a positive headspace where the gently sloping shoulder of the Velopex and the H&H cartridges was found to be insufficient. The H&H cartridges have been proven to be successful in the hunting fields and the target ranges the world over since their creation.

Best.