Chamber Lengthening

[dbear]

I have a BE Grade 1894, good condition with Damascus barrels and 2 5/8 in. chambers. I would like to shoot hand loaded shells with low pressure loads 4000 - 6000 PSI. How significant is the pressure increase using 2 3/4 in shells ? Will lengthening the chamber / forcing cones weaken the barrels ? Which entails the greater risk at say published pressures of 5500 psi. I have used 2 1/2 in Vintager shells from Polywad and similar shells from RST but would like to reload 2 3/4's. I know that there are some who would shoot nothing through old Damascus barrels. I personally know some who shoot any modern target load thru them but that doesn't mean it is a safe practice. Experienced insight and data appreciated.
Thanks,
dBear

[Researcher]

Most American 12-gauge doubles with 2 5/8 inch chambers were intended for 2 3/4 inch shells back in the day. That is certainly the case with Parker Bros. and A.H. Fox Gun Co. doubles. The belief was that the mouth of the case protruding a bit into the forcing cone cushioned the shot charge on its transition from shell to bore, and improved patterns.

There were a couple of articles by Arthur P. Curtis in The American Rifleman in 1936 and 1938 on the virtue of slightly short chambers. Testing by the British Proof house and tests by Sherman Bell, in his series "finding out for myself" which he reported in several issues of The Double Gun Journal, show no significant increase in pressure from firing shells in slightly short chambers.

I don't see any benefit in removing metal from a critical area of a gun barrel.

[dbear]

Thanks Researcher.
Much appreciated.