Yes, that buttstock really IS that good!!
I just picked up this new-to-me '76 with a 28" barrel. The seller said he fired it ten times, then stuck it in the safe. Frankly, this thing looks like it just hatched yesterday. There isn't a mark on it. I can only guess why it was only fired ten times, but if pressed, I would say a lack of accuracy. My guess is that he was firing Buffalo Bore or Jamison factory ammo with .510 bullets and smokeless powder. Given that this bore slugs at .5145", a .510" bullet would make for dismal accuracy. This is what I am using as a starting point:
1:20 tin/lead, 350gr Rapine, sized .514", lubed with SPG
Jamison 50/95 WCF case, primed with Federal Large Rifle Match primers
80gr Goex Cartridge (by weight) through 24" drop tube, topped with .030 Walter veggie wad
2/10" compression
Rounds cycle and chamber with no issues. Magazine holds 11 (!!!)
rounds.
Sometime this weekend, good Lord willing, and the creek don't rise, I will go see if this thing goes "bang" in more-or-less the right direction.