Hi,
I've been handloading subsonics for the better part of the last 15 years (300 whisper, 300BLK, 308win). Couple of my friends and I want to get into the 450BM to load the new-ish Hornady 395 SubX.
Obviously most load data and factory ammo are meant to cycle ARs which means generally slower burn rate, dirtier, higher SD/ES spread due to low case fill.
I'm planning to load using VV Tinstar because its a very fast powder that is more dense that other powders such as N105, LilGun, 4227, etc but doesn't overfill the case like Trailboss, which would probably be perfect for the 250-300gr XTPs.
Now I'm running theoretical numbers with QuickLoad and it seems like I'm near max pressure with a case fill of 80% at around 1050FPS. My question are:
1- Since we're all going with bolt guns and not limited by the AR platform magazine length, would it be a good idea to increase the freebore a tad in order to load these long Hornady SubX maybe at 2.28 therefore lowering the pressure a bit ?
2- I've never handloaded for a rifle straight wall cartridge, but is 39K PSI the true upper limit for 450 bushmaster ? Seems way low for a bolt gun with that kind of case head . So say using CCI 450s primers, new Starline brass and a slightly longer chamber, do we get a bit more leeway on the pressure or 39K is more or less the hard wall ? Was the 39k pressure originally determined by the AR15 platform ?
3- Do you have to crimp at the cannelure ? With these long Hornady 395, seems like if you seat and cramp them at the cannelure, you have to load them at approx 2.220in. Would it be less accurate to seat them longer and not crimp on the cannelure ? I've shot a lot of SMK 220/Lapua 200fmjbt in subsonic and never cared about cannelure position and I would be able to shoot 1-1.25moa at 200 yards.
4- Accuracy. Obviously, subsonic and long range accuracy is a bit of a challenge but in both my 308win sub and 300blk, I was able to get my loads down to single digit ES and shoot a 6in gong at 325yards with ease. G1 BCs don't really matter in the transonic/subsonic world so I was wondering if I can expect similar accuracy (at least 2-3in at 200 yards, with mostly vertical spread).