Chamber lengths

[Austin W Hogan]

Dave has covered this pretty well. A carefull reading of Winchester Shotguns and Shotshells by Stadt shows that 2 3/4 in shells were labelled "for repeaters" on the box. The loading companies pretty well partitioned shells by high base and low base, with the shorter low base shells intended for older and double guns, through the beginning of WW 2. The idea about long shells in short chambers providing a better seal and better patterns did not surface until 1932, according to an article by Ed Muderlak in PP. There are apparentltly some guns made in the 1930's including M21 that followed this, but the 2 3/4 chamber became standard again after WW2.
Blade gauges may underestimate chamber length. The clearance at the mouth of the case is a major safety factor in the event of case failure.

Best Austin