According to articles in the Double Gun Journal about a 100 t0 200 psi increase in pressure.

In a fluid steel barreled Parker I don't shoot magnum or high pressure loads but otherwise I don't think shooting a 2 3/4" shell in a 2 1/2" or 2 9/16" chamber is something to fuss about. Heck, most of our Trojans, VH's, PH's, GH's, DH's and so on have digested their fair share of 2 3/4" shells in their lifetimes, long before we ever became their thoughtful custodians.

That "amazing little hammer gun" is my Grade-4 12 gauge on the 1-frame with 30" Bernard Steel barrels choked Light MOD and Tight MOD. ;)



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Thanks Ed! That is the specific answer I was looking for.

That gun is stunning Dean.

Did any of these DGJ articles deal with smaller bores when it came to the increase in pressure from shooting 1/4-inch longer shells?

Probably forty years ago now, I watched my friend the late Henry Thomas of Federal Oak Farm, Charles County, Maryland, shoot a round of skeet at the old Potomac River Gun Club with this 28-gauge hammer gun, that had been his father's, using factory AAs.

Attachment 113808

It is a Belgian gun marked RICHARD on the lockplates with Twist barrels.

In 1993, Henry gave me the RICHARD. I never fired it and when I left the Capital region I passed it on to a younger Charles County setter man who also knew Henry.

But I repeat myself ;)
Sherman Bell's study is about 1/3 way down here
https://docs.google.com/document/d/1...vwLYc-kGA/edit

His study was for 12g shells, and the average increase was 700 psi.

There is no data regarding the pressure increase in using 2 3/4" modern plastic case shells in short chambered 16g and 20g guns.

It has been established also that Parker cut the chambers slightly shorter than the nominal 12g 2 3/4", 16g 2 9/16" or 20g 2 1/2".
I had a 1924 20g Parker with chambers 2 3/8", and recoil was wicked with AA 2 3/4" 7/8 oz. target loads.
Also, 20g shells in general do run significantly higher pressures than 12g.

We are all free to do what we wish with that information, but not free to make stuff up.