Note that former SAAMI specs for a minimum chamber for the 2 3/4" 12 gauge call for a chamber length of 2.6136" (66.4mm). Minimum chamber diameter at the junction of the cone is given as .798" & a max angle of the cone hrom the horizontal of 5. With a nominal .729" bore this would give a minimum cone length of .394".
One further dimension is given & this is a diameter of .764"at a point in the cone of 2.808" forward of the breech.
Essentially the bottom line is "IF" the loaded shell is not pushed into the cone itself & "IF" the cone is not so short & steep as to prevent adequate movement of the wads upon exit then an exact chamber length or diameter does not truly matter that much.
Max length of an uncrimped hull is listed at 2760", A roll crimped shell @ 2.530" & fold crimp shell @ 2.410". Within these parameters the moist important thing is that the gun itself was designed to handle the pressures & loads under consideration. As Ted has so well pointed out I would not foresee any problem with a French gun bearing the double proof.
Will also not that while SAAMI no longer lists these shorter cahmbers as their recommendation they do note that former, Shorter, standards are still acceptable for use, as long as the gun was made to handle SAAMI pressures to begin with.
This does not automatically apply to guns built to British, CIP etc proofs unless you "Know" the gun was proofed to handle pressures which were in the SAAMI range, regardless of chamber dimensions.
Overloading can & does lead to cracked stocks, loose actions, bruised & sore shoulders, flinch development & etc, but very seldom actually results in a Blown Up gun.
Depending on other factors a short barreled gun can have a more forward balance point than another with longer barrels. Obviously shortening an existing set of barrels will move the balance point rearward. This may or may not work out for any given individual. One simply has to try it & see.
From a purely ballistic standpoint a short barrel gives up virtually nothing to a long barrel one, within reason of course. I have not done a tremendous amount of duck hunting but all the ducks I ever killed were done with a 26" barreled 12 gauge chocked .012"/024" using 1 oz loads of #6 or #5 in lead. Since lead was still legal obviously this was some time ago.
