Brass Strength

[.300winmag]

I was reloading this evening and noticed a faint halo ring on my .308 Win. cases and it reminded me of a study I did about seven years ago in college. I was in a materials failure class and the final project was to take something that was broken and figure out why/how it broke. For me I used my M70 .338 win mag cases. I had been getting 3 reloads from them, then the head would separate.

From my analysis, the material the casing was made of had an tensile strength of 100 KSI, which is typical for brass and it's variations. However, in my .338, I was using loads under Nosler's max load. I used QuickLoad from a friend and found the pressure of my load to be 62,000 PSI, then, by treating the cartridge as a 'thin walled pressure vessel', I was able to calculate the stress in the walls of the casing. This stress came out to be 1007 KSI! Over ten times the tensile strength of the casing.

I found the problem to the case failure to be my FL die. It was set to about 0.010" set back from the shoulder, thus inducing way more cold working/work hardening than needed. Once the die was adjusted, I was getting 10 reloads per case.

Sorry for this rant, but as I was looking over the report, I realized how much energy is contained in one little shell. I'd just like this to be a reminder that reloading should not be taken lightly. . . You can do it right 1,000,000 times, but it only takes one mistake to get hurt.

If you'd like the full report I did, PM me and I'll send it to you. . . I will say it is a little crude, as I did it freshman year of college.

 

[Oldtrader3]

Being old and nearly 50 years out of college, I am not sure I could do that anymore out of memory. However, I did do some stress calculations recently for Bill on Remington brass, half hard, and found that he was blowing primers at 60KSI in his 7mm STI because the cups were brass and not steel.

 

[.300winmag]

Being old and nearly 50 years out of college, I am not sure I could do that anymore out of memory. However, I did do some stress calculations recently for Bill on Remington brass, half hard, and found that he was blowing primers at 60KSI in his 7mm STI because the cups were brass and not steel.

Very interesting! Thanks for the information! If you documented your work and don't mind sharing, I would be interested in looking it over (For personal reasons, and personal reasons alone. I don't wish to exploit you in any way, shape or form). I'd just like a little info to ponder. I've been going through a brass brand dilemma lately. If Lapua still made .300 brass, the decision would be easy. But, now I'm leaning heavily towards Nosler brass.

Thie primer thing you mentioned confuses me. I do not doubt what you said at all. I have seen it personally with a 175 MK and Varget. It just makes me think of .308 Winchester Lapua "Palma" brass that is manufactured to use small rifle primers. I've tried both and never seen a difference. I stick with LR primers however, because I want a guaranteed ignition on cold elk hunts.

 

[Oldtrader3]

I did not save it, unfortunately, I just wrote it up on this forum for Bill and did not keep it. I am too old now to keep stuff anymore. I donated all of my engineering and statistics books to the library about ten years ago, after I nearly died from MRSA pneumonia and had to live in a home for 3 years. No room for memories. Sorry but I am sure that you will understand.

 

[Elkman]

I will look for Charlie's write up, however I am sure that I also eventually disposed od it after printing, and moving once. I also disposed of those ancient primers and have not had another problem. That is the only time when "older" components have failed me. A neck sizing die for a couple of cartridges as well as infrequent annealing has extended my case life "dramatically".