2 5/8" or 2 3/4 " Chambers?

[Kurt Sauers]

I thought I read somewhere that Parker 2 5/8" chambers were also for 2 3/4" shells. Is that true? What about English 2 5/8 " chambered guns? Or did i imagine I read that somewhere?

[John Campbell]

Mr. Sauers:
Most English guns made prior to WWII had 2 1/2" chambers. And some with 2 5/8. Either chamber length will handle modern pie-crimped 2 3/4" cartridges with no issues. I've personally fired many thousands of 2 3/4" cartridges in my own 2 1/2" English guns with NO problems at all. However, these are modest 7/8 or 1 oz. loads. NOT Walmart promo shells.

If you need further assurances, know that Sherman Bell tested this and found only a 50 psi increase in the longer hulls.

[Drew Hause]

John: please add another 0 to your psi rise.
Scroll down about 1/3 here for a summary of the Bell study
https://docs.google.com/document/d/1ZIo0y746UsSRZIgRuuxwAbZjSBHitO_EanvwLYc-kGA/edit
The greatest rise was a 7/8 oz. Estate plastic hull at 1206 fps at a 1216 psi increase.
“Shooting 2 3/4” shells in 2 1/2” chambers does make them produce more pressure-but in most cases it is less than a 1000 psi increase. I see no reason, related to safety, to modify an original 2 1/2” chambered gun to shoot 2 3/4” shells, if the 2 3/4” load you intend to use would develop pressure that is safe in that gun, when fired in a standard chamber!”

To the 2 5/8" chamber question. Yes, the 2 5/8" chamber was designed for roll crimped 2 5/8" or 2 3/4" shells. Most modern 2 3/4" plastic hulls are less than 2 3/4" after firing however

http://pic20.picturetrail.com:80/VOL1373/6511424/24488932/410153970.jpg

I am aware of no study reporting an increased pressure using 2 3/4" plastic hull shells in a 2 5/8" chamber.

I believe 2 5/8" in Ahmerkan is also 2 5/8" in English ;)

British 2 1/2" and 2 5/8" chambers did have different Maximum Service Loads; the 1925 - 1954 Rules of Proof
The 2 1/2” & 2 5/8” 12g maximum service load was reduced to 3 Dr. Eq. with 1 1/8 oz. shot with a mean pressure of 3 1/4 tons by LUP = 9,800 psi by Burrard’s conversion.
The 2 3/4” 12g max. service load was 3 3/8 Dr. Eq. with 1 1/4 oz. shot with a mean pressure of 3 1/2 tons = 10,640 psi by Burrard’s conversion. (Primarily for heavier “Waterfowl” guns)

[Drew Hause]

Will Evans posted this image of 2 3/4" shells in a 2 5/8" chamber, which is very suggestive that the use thereof in his gun is a problem

http://pic20.picturetrail.com:80/VOL1373/6511424/24488932/413248264.jpg

I once had a 1924 20g Trojan with chambers almost 2 3/8" and the recoil was extremely sharp with 2 3/4" target loads, and spent hulls had "feathered" case mouths (on left) likely from entering the forcing cone

http://pic20.picturetrail.com:80/VOL1373/6511424/24488932/412969745.jpg

[John Campbell]

Drew:
As usual, you have the data. Mia culpa.

But my guns still don't seem to care.

[Rick Riddell]

It should be noted those yellow 20ga shells are 67mm from Classic shooting advertised as 2 1/2, the one on the left was shot through a 20ga Stevens with 2 1/2 " chambers the one on the right standard 20 with 2 3/4 chambers. The extra 2 mm was too much for the Stevens.