Now for the question. If I have identical wads (dimensionally), but one weighs more, will the heavier one produce more pressure? My wife (and shooting partner) bought me a new digital scale and I happened to have some Winchester and Claybuster 20ga wads. The Claybuster weighs about 3.5 grains more (average), but are dimensionally the same (have to get some digital verniers).
Yes, ALL THINGS BEING EQUAL, the slightly heavier wad will increase pressures a tiny bit, just the same way that increasing the amount of shot would also do.
That said, the devil is in the details and all things are seldom equal. It is very likely that the Winchester and Clay Buster wads (I also use the excellent CB wads in 20 and .410), have slightly different polyethylene mixtures, even if we do assume that they are dimensionally identical.
Polyethylene mixture difference is a pretty good guess due to the difference in weights and apparent similarity in dimensions. Due to different polyethylene composition or slight difference in design, the wads may obturate differently and this could affect pressures just as much as the tiny difference in wad weight. You really have to pressure test each and every combination. It is very risky to interpolate component changes without actual testing.
I have always found if difficult to accurately measure the dimensions of plastic wads. A little crunching in the bag can change their shape quite a bit. I doubt if digital calipers are necessary, but they would make a nice adjunct to that neat new scale.
One last point, and perhaps one that you already know the answer to-
Higher pressures do not necessarily mean greater perceived subjective recoil or greater mathematical free recoil. They may, but not necessarily. The only thing you know for sure is that higher pressures mean, well, higher pressures.
Bruce Buck – The Technoid
SHOTGUN REPORT’S Guru of Gear
(Often in error, but never in doubt.)