That is hardly the normal Jack-I would be interested in seeing the level of proof on that gun. A few years past, a friend ordered a new Arrietta 20 and specified 20 magnum. Big mistake. The gun he got was not the trim little ballerina he had handled at the dealer, but, a hulking 12 gauge in a 20 suit. It was proofed for 20 magnum, and I would say the Arrietta people did their job well on the gun. It was exactly as it should have been.

I own a 5lb, 13oz 20 gauge. Even if it was so proofed, it would never see 3" ammunition.
Best,
Ted