Franchi, you're talking about an American gun, where really low pressure may not be quite as important as it is on older British or European guns. Our guns were, in general, built stronger--more like tools. That's especially true of guns like Davis, Stevens etc. But back in the 1920's, when Olin came out with the Super-X shell, that raised standard working pressures about 1,000 psi over what they had been previously. So it's a situation of guns not designed for the pressure of modern shells, having suffered some ravages due to age, and metallurgy having improved quite a bit since before WWI. All reasons to hold down pressures at least somewhat, even in older American guns.
