Not having reviewed the entire text and background information, I would guess the W93/W97 is the advent of cutting fixtures that eliminate the need for emery for cleaning up pitted or rusted barrel bores and for enlarging bores to increase the choke constriction.

I have found the same with Parker 20ga bores. Most are a few thousands over .615 up to .620. And most/ many 0 frame 20's have a min under .030, most seem to be .022 to .025. It would be hard to find one with .030 wall.

I’m curious as to why a 1923 gun would have 2 1/2” chambers? Maybe to bump pressure/velocity for trap competitions?

I thought so too, having always heard the 12 bores were chambered 2 5/8 for 2 3/4 shells. When I looked at TPS, however, the factory chart from 1920 clearly shows 2 1/2" chambering as standard for the 12 ga. See Vol. 2, p. 519, Fig. 12-18. I measured them with both a fixed diameter Walker gauge, and my inside dial caliper. Definitely 2 1/2 inches.

That would be 2 1/2" chambers for 2 5/8" shells, the most popular shell of that era.

The "standard" 12-gauge field loads with 1- or 1 1/8-ounce of shot came in the 2 5/8-inch shell, but from 1907 onwards our ammunition manufacturers only put the 1 1/4-ounce loads in 2 3/4-inch or longer shells and "trap loads" whether 1 1/8- or 1 1/4-ounce came in 2 3/4-inch shells.

That said, the 12-gauge Parker Bros. hang-tags I've managed to save pictures of are very confusing, several showing targeting with 1 1/4-ounce and saying "Use Shells 2 5/8" --

Attachment 133867

Others do show 2 3/4-inch shells --

Attachment 133869

or targeting with 1 1/8-ounce and "Use Shells 2 5/8" --

Attachment 133870

Attachment 133868

And that information begs the question “why would a ‘competition’ gun of 1923 have 2 1/2” chambers?”





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VHE
 

This is one of those Parkers that has tons of character. It saw lots of action and served its owners well. And the unique checkering pattern makes it even more interesting.

Here are some pages from a January 1, 1925, Remington ammunition Price List with the 12-gauge 2 3/4-inch loads annotated.

Attachment 133872

Attachment 133873

Attachment 133874

Attachment 133875

Before 1907, Union Metallic Cartridge Co. offered a Load No. 5 or X5 that was 2 3/4-dram and 1 1/4-ounce of shot in a 2 5/8-inch shell which was dropped by 1907, and Load No. 8 or X8 came in a 2 5/8-inch case. Remington Arms Co. used Load No. 8 to target their doubles --

Attachment 133878

Attachment 133876

Attachment 133877

Beginning in the July 1907 UMC Price Lists Load No. 8 and X8 were in a 2 3/4-inch case.

[QUOTE=Dean Romig;430708]And that information begs the question “why would a ‘competition’ gun of 1923 have 2 1/2” chambers?”

I'm not so sure it's a competition gun.