The Disadvantages of the 3-1/2 inch Twelve Gauge Shell
There
are several readily understood disadvantages to a 3-1/2 inch chamber in
an autoloader or pump.
1) Weaker receiver. Anytime you have a larger then necessary ejection
port, you weaken the receiver commensurate with the amount of additional
metal removed.
2) Longer, heavier receiver. To accommodate 3-1/2 inch shells, the receiver is longer and heavier than otherwise necessary, as is the shell elevator, links, mainspring tube, etc. The shell elevator and associated springs must be heavier to move around a heavier object, the loaded shell itself. Contingent on the model, loading through the bottom of the receiver can be clumsy, finger-pinching, or a bit of both.
3) Slower cycling. It is a matter of distance: the bolt most travel rearward half of an inch farther during the ejection sequence, then must again travel and additional half of an inch forward to return to battery. It indicates a slower-cycling autoloader and a slower to shuck pump.
SAAMI Shotshell Maximum Average Pressure (MAP) in PSI
10 gauge 11,000
12 gauge 11,500 (except 3-1/2 in.)
12 gauge 3 1/2 in. 14,000
16 gauge 11,500
20 Gauge 12,000
28 gauge 12,500
.410 Bore 2 1/2 in. 12,500
.410 Bore 3 in. 13,500
4) Heavier than necessary barrel. Only the 3-1/2 in. 12 gauge shell deviates substantially from standard 12 gauge 11,500 PSI MAP pressures at 14,000 PSI MAP. With the approximately 22% rise in allowable working pressures, the barrel must necessarily be thicker and heavier than otherwise necessary to accommodate the additional working pressures.
5) Thicker, heavier components subject to recoil. When shooting some 3.5 inch shells, for example a common 2 oz. 1300 fps lead load, your shotgun and its stock are subjected to elevated levels of stress, shock, and vibration than they would be with lower recoil 2-3/4 and 3 inch shells. All parts of the system punished by the additional shock must be made heavier and stronger to accommodate the higher intensity load levels. The bent mainspring tubes and cracked bolt buffers that have plagued many models get far more stress from 3-1/2 inch shells.
Patterning is often debated, with folks such as Browning publishing their findings that pattern percentage improvement of ten percent or so is experienced when the unfolded shell length matches the chamber. That generally is not of great concern, for if you need an extra .005 in. or so of constriction to get the pattern percentages you want, you just use it.
None of this should dissuade you from getting a 3-1/2 inch 12 gauge if that's what you want. Like a lot of things used for fun and recreation, things don't have to make any sense. If you want it, that is all the reason necessary. Manufacturers are loathe to make more components than necessary, so too often a shotgun that is designed for 3-1/2 inch shells isn't as compact, responsive, or as intuitive to operate as it could be if the action was designed around 2-3/4 in. or 3 inch unfolded length shells.
Copyright 2012 by Randy Wakeman. All Rights Reserved.
