Al, this is a good question: " Leaving the issue of velocity needed to be competitive in todays BR world aside, is a shortened 6PPC the real answer to efficiency in 6mm BR case? "

AND, it may very well be that shortening the case, while using, say N130, or even N-120, could safely produce equal velocity while providing lower muzzle pressures.

The pressure curve, using the BR case as an example, illustrates the the reality that "burn-rate charts" are merely a ball park deal - burning rates DO change relative placements as expansion ratio changes - just try shooting 34.8 Gr. of H-4198(extreme) combined with a 100 Gr. bullet via your 6BR . . BUT, Before you pull the trigger, make certain that your will is up to date, notify your next-of-kin AND call an ambulance! ;)

When combined with a thirty caliber bore, bullets of 125 Gr. or less, and the BR capacity , H-4198 verges on being too SLOW; it may perform even better via a capacity somewhere between a 45.5 Gr capacity (about a .30x44) and 37.0 Gr. capacity(.30BR) case - something on the order of a 30x41! IN either of my current 30BR barrels, case volume, NOT pressure, turns out be the limiting factor with regard to how much H-4198(extreme) is too much!

Then, regarding the 7.62x39mm Russian Improved (a.k.a. 30 PPC), again, powders is the burn-rate range of N-120, H-110, 1680, etc., may prove uesful - I had/have no interest in messing with the russian case. Also, early on, I shot some very respectable group Aggs, including registered sub .25 MOA jobs, and VfS scores using H-4227 @ about 29.5 Gr.   - about the same burning rate as N-120 . . HMMMmmmmmm.  .  . now that we've developed a little courage, maybe we need to revisit tipping the can again!

Bottom line, we opted for the BR case because, compared to a 30x41 or 42, it is EASY to form; and case forming is another area where where people run into problems . . . BUT there is a whole world out there waiting to be discovered!

Keep 'em ON the X! R.G.