7.5 French Blow Out

[dh1633pm]

Took the MAS36 to the Range yesterday to test out some loads. The load being:

Converted RP Brass in 30-06. 150 Grain Hornady FMJ behind 37.5 grains of IMR4895. Got the load out of my current Hornady Manual Page 393.

Shot about 15 rounds of 20 loaded. All shot fairly light, low recoil, including the one that suffered a blow out. The last round shot some dust in my face and then the bolt couldn't be opened. I used a wooden mallet when I got home to open it. Rifle doesn't see no worse for wear. Opinions? Am I a duffus or just plain not very smart. Been loading for a while. Keep a log of everything. I always check, check and double check. Pictures are about as best as I can get.

 

[Dog Soldier]

Well old friend there is one thing we know. The case had more internal pressure than it could contain. Was the neck too long or too thick? Could the case have had less water capacity? Was the base heated too high while annealing? Step by step it will be exposed.

 

[dh1633pm]

It was an RP and not a LC like the others. Thought I had sorted all the RP brass out. Not the case. It could have been heated too much. I used the drill method with the flame in a vise. I do think I going to buy some purpose made brass.

 

[dh1633pm]

I am going to pull the bullets from the four remaining rounds and weight out the charges.

 

[Dog Soldier]

The Remington Brass has less capacity than does Winchester. I expect however it would close to the Lake City? The more I observe this heat may have been the culprit? More than one case failure has been traced to the annealing process?
Just speculation by me, no facts or links to prevail.

 

[hdwhit]

Dog Soldier wrote:
Was the base heated too high while annealing?

Good catch for a possible explanation.

As relates to my other post that you commented on, this is why I haven't taken to trying to anneal the neck on my 5.7mm Johnson cases. With a length of just 1.3 inches, it would take exquisite control of the flame to get the neck soft while not softening the head.

 

[hdwhit]

dh1633pm wrote:
I used the drill method with the flame in a vise.

In the Hornady Handbook #4, they recommend sitting unprimed brass in a pan of water that is deep enoough to fully immerse the case head and go about half way up the body, annealing one case at a time and then after giving it a moment to cool, tipping it over into the water to quench. The water bath greatly slows the migration of the heat towards the case head during the time heat is applied.

I know that some months ago there was a thread on annealing where one of the posters said it was bad to quench the heated brass, but given the properties of metals with a face-centered cubic structure, I don't think such a quenching - provided the brass is given a moment to cool before being quenched - presents a problem for an alpha brass with 70/30 copper/zinc content.

 

[eastbank]

the answer for me was to throw all the reworked brass into the junk barrel and to buy enough privi 7.5x54 factory french ammo to do me. i have reloaded them 4x times with out any problems at all. eastbank.

 

[dh1633pm]

Eastbank, I agree with you already. I am going to buy some purpose built brass. I see midway and others have some in stock. Nice french rifles by the way. You must have one of everything.

Do we think its the brass or an overcharge?

 

[eastbank]

looks like a lot of pressure, i don,t think it was a over charge, hornady lists 42.1grs imr 4895 as tops, so your charge of 37.5 is about 5grs under max. but i,m no expert. thanks to a good desined rifle you were not hurt, thank god for that. i shoot both my french rifles, i did put a adjustable gas valve on my 49/56 so cases stayed in this county. eastbank.

 

[Blue68f100]

Wonder if the neck was thicker causing the bullet to wedge when chambered.

 

[dh1633pm]

It could be that the neck was thicker. Didn't appear to be so. The neck looks perfect now.

 

[dh1633pm]

I had four rounds left over from the 20 that I made. I pulled the bullets and weighted the charges. Two at 37.5, one at 37.4, and one at 36.8 (huh?). That was weird. I checked each of the empties. There was an RP in the empties. Along the base of the empty it was much bigger than the LC brass. I will order some 7.5 brass from Midway in the next day or so. Will continue to look at things.