That's a lifter with the breech face to water table not be square in the corner but rather radiused .

Ah!.... Thank you.

I was surprised find out how many lifters were chambered in 2 7/8's. That shows what making assumptions does. I am glad I asked this forum and appreciate all of the responses.

Just curious Bill. What are the perceived disadvantages of square corner chambers?

I've had a couple folks tell me that the square corners stress more and or crack there easier then the guns that have a radius in the corner . Whether that rings true or not I do not know , but when I got around to buying a lifter gun I made an effort to get one with a radius . And it still needed a good bit of work (but it wasn't cracked), but for what I paid and the fact that it was made in 1881 I think I still came out okay .

There seems to be some confusion between chambers that were cut for metallic (often brass) cartridges (square chambers) and the 90 degree angle of the action flats intersection with the standing breech (also referred to as square cut) on the earliest lifters. Later Parker Bros modified this 90 degree angle by machining a radius to this juncture.
A number of the early (square cut) guns suffered cracking at this juncture and the word today is that "If you shoot it often enough, it may crack." Evidence suggests this may be more than just rumor.

The chambers that were cut for metallic cartridges don't crack that we know of. I have a few of these guns and shoot them with the appropriate RST loads and never give it a second thought. If your plastic shell opens beyond the end of the "square" chamber it is no worse than shooting a 2 3/4" shell in a gun with 2 5/8" chambers... maybe an increase of 100 p.s.i.

When I started this thread I was afraid(In a good way) that I would have a 10 gauge soon. I did find an early gun(1874) D grade I couldn't live without.

It has 32 inch barrels(which was my preference in a 10) and an English stock which I also prefer. It has 2 7/8 chambers, which I also I wanted and is choked IM/F. I went out of my budget to get it, but it will be my first D grade.

Since it is an early gun it will likely have the square chambers discussed in this thread. I am only going to shoot RST and low pressure equivalent shells(when I start to reload 10 gauge). Hopefully, I won't have any issues with light loads.

I won't have then gun until early April, but I will post pictures as soon as I get it. I already ordered my Parker research letter. I am looking forward to shooting it at the Southern SXS.

Thanks again for all of the suggestions and advice!

Jay

Congratulations on your acquisition. Looking forward to the pics