Sean Wilson`
10mm Magnum continued
Friday, April 15, 2022, 12:44

It occurs to me that I left some stuff out of the original post. I've been resizing 41 mag cases to use as rimmed 10mm for most of the 12 years I've had my original 610. I actually have 2, a 6.5 inch and a 4 inch, but I was trying to keep the initial inquiry based on the 4 inch I'll be carrying most often. Both were converted just recently.

One thing I do know from resizing the 41's for use as 10mm is that the case volume is somewhat reduced from the original rimless 10mm cases. Additionally, 41 mag cases, according to Starline are 1.285", while 10mm mag cases are 1.250. Having swaged down and trimmed the 41's to 10mm really squeezed the capacity, and my go-to load for that ended up being a compressed load of 10gr of 800-X under a 200gr cast bullet. It's a hot load, but shoots the best out of anything else I've tried. Magnum powders (296, 110, etc) just wouldn't work well at all in the short case.

I did try to pull up what was available or the .401 Herters, and the case length is pretty much the same as the 41. So, with the swaging and the trimming, I would be hard pressed to believe that the case volume would be the same between 10mm and 401's....I don't know how much that 0.035" would matter, if it all, but I did chase a rabbit hole to see what I could turn up.

I agree with Gary that starting with 10mm data and working up will work for some of this, and there's the already published data for h110, 296, AA7 and AA9....but I'm now into the magnum level cartridge and would like to see if I can get some performance from the 3 other magnum powders I have.....namely, the 300-MP, Enforcer, and N105.

As far as bullet stock, I have a buttload of 200 grain cast from Missouri Bullet, and they have some 220's I'd like to make use of that were just too long for the shorter case, but should work dandy in the magnum. I have the Lee .401 sizer, and have resized some bullets in the past, but I'll save that task for now and maybe make use of it when the time comes that I want to venture into REALLY heavy bullets. Best I concentrate on the basic part of it that I'm on right now.

I hope this helps everyone understand where I'm at and where I'm trying to go. I'll probably invest in a chronograph sometime soon to help with development. Just off the top of my head, I think a conservative goal at this time is to aim for pushing a 200-220 grain pill between 1350 to 1550 feet per second.

So that's my thoughts so far.