Very extensive testing was done on this subject in England with the introduction of the fold (Pie) crimp shell. This was reported on in depth by Burrard in his book "The Modern Shotgun". The result was that virtually all British shells marked for 2" chambered guns from that day forward & closed with a fold crimp have been longer than their nominal length.
Most British shooters of this era were not reloaders & bought their shells as loaded for their guns. It is quite possible not many of them were in fact aware the hulls were indeed longer than their chambers, Therefore they seemed to have no problems with either excess pressures, excess recoil or poor patterns.
But let the Cat out of the Bag, Then Kattie Bar the Door!!
For whatever reason Bell was not willing to accept the work which had been settled for some 50 years or so & had to "Do it Himself". His work perhaps brought it to the attantion of a few people who were unaware, but in reality to the extewnsive testing hich had proceded him he was was inventing a solid rubber tire while we already had the Steel Belted Radial. Shells being fired in chambers of a slightly shorter length than their fired length than their chambers is a proven safe practise as long as the shells are loaded to the appropriate pressure level.
The one big Caveat which was mentioned by Burrard which no-one seeems to mention is that shells should not be fired in a chamber shorter than their "Loaded Length". This results in the mouth of the loaded shell being forced into the cone of the chamber, in effect increasing the resistence to the opening of the crimp. Very few 12ga guns will be found actually having 2" chambers, the majoprity being from 2 9/16" (65mm) to 2 5/8" (67mm). The loaded 2 3/4" (70mm) fold crimped shell measures about 2 3/8" (60MM) long. There is ample clearence between the end of the shell & the start of the cone for the crimp to open unrestricted. There is thus little likelhood of an actual increase in max pressure, but perhaps a slight slowing of the drop from peak. I personally have serious doubts that Bell recorded enough data to postively establish much of anything as absolute fact. It is noted though that he did not come upon anything which disputed that which was already established & had been in practise for years, which apparently he was unaware of.
