There have been many many threads about this, and lots of theories. It happens often enough that there is a decent argument that it happens for some reason other than over charging, but then it hasn’t been replicated.
Correct. I read the listed thread again this morning.
One, to begin with, this is a very odd choice of powder, for the purpose he intends. I am no expert at all concerning the type match they were shooting, along with whatever common practices they might be working with. AA 5744 is very commonly used in a variety of cartridges for reduced loads. I also had a look at the AA manual and AA 5744 is listed for 30/06 for LEAD or cast bullets, 160 gr to 200 gr, 22-27 gr giving around 2000 fps. No mentions for any other bullets in this cartridge. I can't even imagine where or why one would choose this powder for I believe it was a 155 gr jacketed bullet. ??? However, that being said I have done a lot of things that are way out of normal, and have even blended my own blends here in search of "magic Powder"................
He states he was using 30 gr of AA5744 with the 155 gr bullet. Also stated he had fired up to 75 rounds of these prior to this match. Obviously no issues. Then fired two rounds in this match, and fired the 3rd which blew the gun.
Thats 77 rounds fired, no signs of pressures and now all the sudden there is the ONE ROUND that blows the gun......
There are about just under maybe a MILLION other reasons this could have occurred, and maybe not a 50% full case. I blew a gun one time, but I broke the rules of paying attention to what I was doing! Loading a 6.5 WSM, slow powders, and I think the test load was H-4350, or was supposed to be. Phone rings, I get on the phone, not paying attention, I pick up a can of H-4198..... It was "H"................ Not good results, locked it up tight, worse than just locking it up. Pressures would have well exceeded 100'000 PSI I am sure. Gun held together, but was stretched beyond use again.......... Picking up the wrong powder, distracted by the phone and probably more stupid stuff too....
Yes, it might have been undercharged! The 2cd round fired in that match might not have had a full charge. So much so, that the bullet stuck in the barrel, and the 3rd round had no release for the pressures. Ka-Boom!
And many other things too........
While I won't totally 100% dismiss the "light charge-larger case volume" possibility, I seriously have doubts, if for no other reason that I have done it 1000s of times with various different cartridges, powders, and combinations.
While the vast majority of the time, when I go to lighter charges, I use a faster powder, there have been times I worked with much slower powders. We have worked with fillers here many times, fillers are commonly used in big nitro cases to remove the air space. Extremely large cases like these do odd things as well. I mentioned above about Hang Fires, and fillers are used to try and stop this sort of thing from occurring. Fillers can be dangerous, far more so than half filled cases, or hang fires. We did a filler test once with 470 Nitro to prove the point.
I did a google search on this as well. I did not spend very much time reading anything in detail mind you, but every case I saw was much the same as JimB states above.... Lots of threads, lots of theories.... and has yet to be replicated in the lab. My Theory? My theory is this, if it can't be replicated under controlled conditions, repeatedly can't be replicated and proven, then I would tend to believe that other factors are involved.
Everyone can screw up at the bench. I have, I suspect many of you have as well. Not saying anything, just saying "S**T Happens".
Have a nice day.........