I made a die & mocked up an approximate case, as no dimensions but case overall length 1.293" was given 52, 000 psi operating pressure.
I made it .010" short to barley cover the 300 gr Berger ogive .3375" a slight crimp will take care of that, at 1.283"
I measured the case capacity of the cut down 6.5 Grendel case, shoulder dimensions & body taper may be off, but no print to go by.
The H2O capacity was 29.0 to 29.2 grains at 1.283" the case capacity for the 338 Spectre is listed at 28.8 in QL, as slight difference in COAL and body dia. There are 2 max pressures given one for pistol brass and one for 6.8 brass. QL uses the lower pistol brass load 37,500 psi and rifle brass was something like 55,000 psi...something to check out.
But just plug the numbers into the 338 spectre data, change the COAL, case capacity , & case overall length.
With 300 gr match bullets, in a 12" barrel QL predicts the pressures will be close to max with a variety of powders at around 1200 fps.
Which should give good sub accuracy, and consistency.
W296, 1680, AA9, AA 11FS, 2400, LILGUN, H4227, IMR 4227, CFE BLK, were all in the try area.
The 4227s, and CFEBLK were getting compressed at just over 107%
W296 and LilGun , ate the first I'd try, with 300 gr match bullets.
Charge weights look to be around 10 to 14 gr with those powders, & 300 gr match bullets.
200 gr in 12" barrel looks to be around 1600 fps
160 gr Barnes tops out at 1900 fps area.
All a guesstimate on what to expect.
The Spectre has a 6.5 twist and Maker makes a bullet for sub hunters to try in the Hornady 338 ARC 8 twist, that might work, the twist rate makes a difference on opening these bullets. (In my tests, LOL)
Maker also make a light 160 gr super expanding for the Spectre to try in the ARC, for those interested.
I think the 338 ARC will make a good sub sonic gun, with good barrels, and their may be a mag feed issue with the larger 338 bullets, plus barrel extension mods for proper feeding...the industry should take care of most problems, as they arise, as Hornady being behind this should help, if not you'll have to do your own modifications.
