doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com Is it a 2 1/2 inch or 2 3/4 inch chamber if it is

an English shotgun, most likely made between the wars, with no mention of chamber length on the barrels or flats? Thanks

Hi Pooch, what is the bore and shot weight on the bbl flats? Also a pic of two of the bbl flats should help.

Be Good!

Greg

Most likely 2 1/2". However, do not translate 2 3/4" chamber into OK for use with SAAMI ammo (that is mostly what you can buy in USA without special effort like mail order). Even if it turns out to be a 2 3/4" chamber it will need care and feeding with CIP standard ammo and/or reloads of known pressure (SAy, sub 8000 psi).

DDA

2" is also possible although they are usually identified by a special model name as well as on bbls/water table.

The English proof was based on tons per square inch and not the chamber length in the barrels. One could find gun with 65mm chambers proofed for heavy 1&1/4oz load, etc....

Very true, but Tons psi (Birmingham proof) or "Tons" (London proof) markings are under the Rules of 1954. If the gun is between the wars, then the chamber "should" be marked "2 1/2", 2 3/4" etc" and not in metric mm's.

Shot size should give you a feel for what the chamber length "might" be. If the gun were a 2" it would be marked on the rib also. Best bet would be to just shoot 2 1/2" low pressure loads in her to be safe.

Best of luck!

Greg

Best bet is to get off the cheap and buy a chamber gauge. It always amazes me, how so many men will step up on their dime [time] and try to answer questions like this. CB

Pooch may just want to know what the original chambering was and just wants to see if the chambers have been let out.

But I agree for the current chambering, a gauge is the only way to go.

All the best!

Greg

A 6" flexible machinist's scale is quite adequate for measuring the length of a chamber, even one of the inexpensive ones from your home improvement store will do fine. It is in some few cases even more accurate than a chamber gauge. Simply hold the bbls up toward a light, I normally use a window, & look in. move the bbls around till you have the cone thrown in a shadow. Slide the scale in where you can view it & watch for it to come flush with the shadow line. Do it a few times to ensure you are being consistent. With only a few tries you will find you can easily read the depth to within the 1/64" markings of the scale, plenty close enough for measuring chamber depth.

Should the chamber be a bit undersize, not uncommon on older guns, & be only .001" smaller at the end than the diameter of the gage, the gauge will show it about .200" short, which it isn't. The case where the scale is actually more accurate.
An old saying from my youth, "There's always more than one way to Skin a Cat", there are simply not many "Only Ways" to do anything.

Not quite, Greg. 2 1/2 or 2 3/4 would not have been marked under the proof rules of 1904, which remained in force until 1925. On guns proofed in 1925 or later, you will find chamber length. That's a quick and easy way to distinguish a gun with pre-1925 proof from one with post-1925 proof. Otherwise, those two sets of proofmarks are pretty similar.

Rocketman's caution about 2 3/4" shells is also spot on. And another thing to be wary of would be guns which have been lengthened to 2 3/4" in the States but not submitted for reproof. You'll find quite a few of those floating around on the market in this country. Too many, in fact.