The 12GA Fh is 12ga chamber in heavy barrel, heavy strong action, that takes brass case 3.85 inches long. Chamber still will fire regular 3in shotshells. Cases are made from bmg brass that we put a 12ga size rim on.rim machined and case machine wit rimm threaded on, no heat
or soldering to weaken brass..Brass can be shortened for shorter chambers.I just use full loads of slower powder,with 90% plus fill.No wads or cards, example load is 280 gr of H-335 ball powder under a 3/4oz Barhes 12ga sabot. Now you can use shotgun powders and wads, like the heaviest that is used in plastic cases and work up for my Savage. Brass is super,as I have case loaded over 25 times and never had to resize bottom 2/3 of the case.