04-30-2020, 01:01 AM
SPECTRE66 Wrote:Hi All,
I just posted earlier, in the Reloading section, about fire-forming some brass. I've just completed resizing 4K rounds of Winchester 762X39, to 6.5G.
My question was, with a 123gn bullet over 25.0 gn of WIN 748, will I incur a pressure spike, due to the large rifle primer.
Since some of you have 'more than dabbled' with the 762X39 conversion, and you're still here, I think it's safe to infer I'm on solid footing, regarding fire-forming.
SP66:
Pressure spike? Who knows?
We had to use less powder because the 7.62 X 39 brass is much thicker than Grendel brass and so had less volume and thus probably produced higher pressures.
After messing with the 7.62 X 39 brass formed to fit the Grendel chamber quite a lot, I found the donuts that appeared in about 80% of the cases after either the fireforming or first shot to be more worrisome when considering pressures. A donut is like a bore obstruction in the brass itself and is a prime cause of blowing primers and other pressure issues. Luckily I had an internal reamer that was small enough not to take off the inside of the neck but big enough to cut through the donuts that appeared in eight or nine of ten pieces of brass.
Not sure how much any of it mattered since no matter what we seemed to do, we only got two or three shots after fireforming before the primers would start to blow or just fall out of the primer pockets.
4K pieces of that stuff ought to last you a while though. My advice is to buy a internal reamer and take out the donuts that will occur.
LR55