Some older (late 40s - early 50s) East German 12 gauge guns were proofed for lighter loads than their 70mm chambers would suggest. At least, their owners' manuals suggest using shells with pressures no more than 420 BAR. I don't know if it relates to the maximum or average pressure, but the practice of using these guns suggests that routing firing of 36 gr. of shot loads (1 1/4 oz) results in play in the action very quick, while 32 gr (1 1/8 oz) loads are perfectly O.K. Later guns seem to be made stronger (and heavier). Anyway, if you stick to the good old 1/96 shot weight/gun weigh ratio, you shouldn't be worried. Unless you shoot buck shot or slugs, it is possible, but should be tried with care.
