Did you confirm both the weight and type of powder used for these loads???
Case 1 sounds like an overload.
Case 2 could have a tiny hole in the side of it.
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saeed@ emirates.net.ae
www.accuratereloading.com
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LSF/375
Charlie Petty wrote an interesting article a few years back on a Swede Mauser being pressure tested in an ammo lab as the company was developing its factory loads. I'll try to relate from memory the story. If I can track down the 'zine that has it in my archives, I'll correct any misstatements made from my oh-so-fallible memory.
*Note* there is no guaratee that the following represents your scenario, but it is interesting. I strongly recommend corresponding with Charles Petty about this. I think he still writes for American Rifleman, and could probably be contacted through them or whatever magazine is publishing his stuff.
Since it happened in a lab, strain gauge pressure readings were available for each shot.
A series of loads with a 140 grain bullet and the same powder charge were fired. They were using a relatively slow-burning powder. The pressure began to rise with each succeeding shot fired, though the powder charge stayed the same.
The pressure curve showed a short upward swing upon ignition, followed by a sharp drop, then a huge upward spike. The lab tech stpped when pressures were over max but before the gun was destroyed. As I recall, after examining the situation, they continued firing the same load and tracking pressures, which continued to climb, and the action let go after another 2 or 3 rounds.
They decided the symptoms looked like: Powder is ignited by primer & starts to burn, pressure within cartridge case begins to rise as expected.
Pressure moves bullet forward into long military throat, dramatically reducing pressure inside the case.
Heavy-for-caliber bullet lodges in long (probably rough) military throat as the pressure in the case was sufficient to discharge the bullet from the case, but not sufficient to overcome friction & inertia and push the relatively heavy bullet from the throat into the bore before the pressure drop occurred.
When the bullet stopped in the throat, it became in essence a blockage in the bore, and pressures elevated rapidly.
Since the bullet stopped moving in the throat, Each shot left more jacket fouling in the throat and made it harder for each succeeeding bullet to be accelerated from a dead-stop in the throat to moving down the bore. Thus, pressure increased with each shot.
Apparently when using slow powders in rifles with military throats, you can reduce a charge too far, especially if heavier bullets are being used. Responder Dutch hit it on the head, I think. If you don't need the velocity that slower powders can produce, move to a faster powder. When using slower powders with long throats, use a mid-to-safe-maximum charge. You might also consider magnum primers to try to ignite more of the powder charge initially.
To be redundant, on purpose, I suggest you try to get hold of Charles Petty to see if he will send you a copy of his article and advise you on any further info that has developed. Then, of course, share it with us. ;-)
[This message has been edited by BigIron (edited 10-01-2001).]
I know exactly the article you are referring to. To add on, what precipitated the test you describe was standard load testing by an ammo company. Phase 1 was pressure barrel testing w/universal receiver -- all OK. Phase 2 was trying the same load in an actual M96 rifle -- rifle blew up but barrel survived. Phase 3 was what you relayed, the M96 barrel attached to universal receiver and strain gauge. Good article but it never completely deduced why the pressure hitch occurred. I suspected a worn throat but that was just a WAG.
One thing about BEJ's story that I'm curious about is the new barel. Could be the neck was chambered a touch short. Headspace with FL resized cases could still be OK but case necks, even when properly trimmed, could be pinched. Given that other rounds shot OK, pinched necks may be far fetched, but it's just a thought. Otherwise check your new rifle against a current lot of cannister powder with a known behavior (e.g., H-4350, RL-19). Use the recommended starting load and work up. Just to be safe, try another lot of brass. If the problem persists, take it back to your smith and have him check it out again.
Good luck and be safe.
Martindog
Old surplus brass, or any "old" brass that has aged is a source of many problems.
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Ray Atkinson
I wasn't sure if you were talking of case head seperation or lengthwise splits. Anyhow I do believe that rem 6.5x55 brass has the base diameter of 30-06 or at any rate is smaller than CIP measurements for 6.5x55. I also feel that it is harder. Add in a larger mil spec chamber and you may have an answer as to why splitting occurs.
In addition it may be manafactured shorter so when fired in a rifle will have to stretch more than winchester brass. This will lead to case seperation allthough to seperate on 2nd firing is pretty poor and would lead me to check head space/chamber.
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Safety & Ethics,Accuracy, Velocity, Energy
Joe M
My Rem and Winchester 6.5x55 brass is a few thousandths smaller in head diameter than the Scandinavian milsurp ammo I have. I'll be ordering some Lapua brass - on sale at Midway this month, by the way, I believe about $38.00 per 100.
Eric
Exercion3@home.com
What was the exact case length on the rounds in question? My guess, one long case and or slighly shorter chamber than spec coupled with a lot lot of surplus powder that is faster than the data used for starting.
I am using some surplus Winchester powder (Vietnam Era .30/06 Machine Gun loads--per the label) similar to Win785 in my 6.5x55's Mauser and Remington, with excellent results. However the loading data that came with the powder was not the best.
The first batch out of the press, with starting loads, produced unacceptable case head expansion, high velocity and excellent accuracy and short case life, (3 loadings)but it drove Sierra 140 Grains at 2900 FPS out of an 1896 M38....case life and accuracy are much better at 2800 FPS and in this case 3 grains less than starting load recommended powder charge.
Item number two seems like a pin hole--the start of a case split.
[This message has been edited by Fish Springs (edited 10-22-2001).]