A long story shortened to I needed a cartridge rim to fit a bolt face then fitted a caliber barrel .
6.8 data works fine up to 130 gr but I want use the whole of the available twist . Not a problem with cast I would just use Unique and a really slow rifle powder and pistol primers until they go flat , run out of case , or get the paper results and desired speed .
I've done a 200 gr 7.62×39 with a paper patch......
I have 180 gr HPBT in 7mm . I have made a dummy at 2.475 that gets me .003 . OAL is only limited by the throat which has been a problem for the 7mm-168 at 175 gr . The twist is 1-8.5" that might be too long for the bullet if it doesn't work no big deal . One calculator I used said 1.8" long bullet would be stable out to something ridiculous like 230 gr .
The 6.8 case for all practical purposes is the same eyeball capacity as the x39 probably a little more. The bullet a Sierra 7mm 180 gr match king with a .660 BC down to 1600 fps and .610 below . It also at 2.475" OAL has the whole BT and a little bit below the neck.
Of course as I've walked through this most of my initial concerns about A; pressure and B; being able to get enough 4350,4831 or H1000 in the case to reach 1900 fps MV have been mostly resolved. Now whether the 20" barrel will deliver or not is the question .
The x39 with the 200 gr PP was just above the 30 kpsi clean up point of IMR 4350 with 22 gr to fit in the mag and 25 gr single fed . I think dropping 20 gr of bullet weight will off set the .312 down to.284 . That just leaves me with is the IMR 4350 still to slow to hurt or should I jump straight to 4831 ?
My hunch says this will be the meat and taters for the 4350 edging towards the top at something like 45-48 kpsi that leaves me about 7kpsi for normal operation on the action design and 10-12 on the brass. If I'm wrong the action has been proven to 75kpsi .
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