yobyllib,
I have shot lots of handloads and lower pressure factory loads (known to be lower pressure from independent pressure testing) that gave measured velocities of about 1250 fps with 1,0 to 1 1/8 oz of shot in my Lefacheax M 15 12X65 and various toplever, sometimes crossbolt guns (made 1890 to 1921), mostly for hunting, with maybe max of 70-90 shots per year/per gun. Mostly, 1,0 oz 1.300 fps loads were used -- that is, loads they were designed for. These loads gave chamber pressures or 9.500 to 10.500 psi at 70-80F and were used at 60F to well below freezing. The guns all have 65 mm chambers and hulls were 65 or 67 mm long. Weights are from 6,2 to somewhat over 7,0 lbs. After years of this, I see no indications of guns getting off face. I never fired USA factory 3 dram loads in any of these guns, in part because of expected higher chamber pressures and known 70 mm hulls.
For busting claybirds, we use 7/8 or 3/4 oz loads at 1100-1250 fps and chamber pressures below about 9.500 psi.
I would expect steady use of SAAMI spec, USA-made shotshells to slowly put at least some older Husqvarna doubles off face because of higher chamber pressure specs for SAAMI than for CIP and similar specs (for which these guns were designed -- that is, somewhat lower average service pressures). All my guns have solid wood in stock around sidelocks. What case is for post WW2, internal hammer, A&D-type Husqvarna doubles (310s etc.), someone else will have to tell us.
Niklas
