I am looking at British box lock for sale. It is proofed at 1 1/8 oz. Nice gun, however somewhere in time, someone lengthened the chambers from 2 1/2" to 2 3/4". It's here in the States, not in England. It appears to have adequate wall thickness (.040") and tight bores (.023").
Would you:
Pass on the gun because it is out of proof,
Expect a significant discount on the asking price, how much?
Buy it anyway and shoot 2 1/2" RST shells and enjoy it.

The only constant in life is change.