In Actuality both Chambers cut intentionally shorter than the shells for which they were intended & shells loaded into cases which were intentionally longer than the chambers for which they were intended predate the plastic era with roots well back in the paper case days. In England in the late 1930's with the introduction of the fold crimp shells were intentionally lengthened with their "loaded" length being similar to the length of a roll crimped shell. It has been mentioned here many, many times the Parker Bros as well as some others makers intentionally cut their chambers about 1/8" shorter than the shells for which they were chambered & this while paper was "King". Until fairly recent times SAAMI specs for the 2 3/4" 12 ga chamber called for a minimum length to forcing cone of 2.6136" to a dia minimum of .798". A minimum dia of .764" was called for at a point 2.8079" from breech with a maximum length of an uncrimped hull of 2.760". Thus if a max hull were fired in a minimum chamber there would be .1464" of hull lapping into the cone. These specs were in effect well back into the days of Paper hulls. The important fact is that in the one case the shells carried a load which was compatible with the guns for which they were intended while on the other hand the guns were built compatible with the loads carried in the shells for which they were intended to fire.
