Berrien, there is to much information missing from the sales promotional data to allow hard and fast scientific conclusions. An Indication of a possible cause lies in the SAAMI maximum average pressures for each gauge, listed below:
10 ga 11000psi
12 ga 11500 ( except 3&1/2" shell =13500)
16 ga 11500
20 ga 12000
28 ga 12500
Even with a constant wall thickness the higher pressure would largely be accomodated by the increasing ratio of ID vs OD in the hoop stress.
Regarding the apparent gain in speed of @ 100 fps This may be a function of decreased friction, however before you could draw any firm conclusions on this I suspect you would need to conduct extensive testing on this aspect alone.
Unfortunately until I win Powerball I cant afford the time and expense to conduct such research.
