Before the advent of the 2 3/4" 12ga shell did Parker make the chambers 2 1/2" for shooting 2 5/8" shells?

There is No issue. Later Parker chambers were cut to 2 5/8" to be used with 2 3/4" shells. This way, the shells would open 1/8" into the cones, thus ensuring a better gas seal.





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Pete, yes.