Mike, it is simple numbers. 16's just are not that common any more. I have them and others do as well, but 98-99% of ammo sales are not in 16 gauges. The 12 has to be 70+% of ammo sales, then 20 are 20%. The 28 might be 3-4%, the .410 is another 4-5%.
As to the 20-16-12 difference. The 16 is stuck in a too small gap. A highly efficient 20 can duplicate a middle range 12 shell and the entire range of 16's. The 16 can be loaded up to 12 middle range range or down to 20 but not that well unless you reload. There are still a very limited number of factory shells to choose from. I did not mean to hurt any 16's feelings and please accept my apologies if I did.
Stan, I agree about shot as there is very little difference between 7, 7 1/2 and 8/'s in high quality shot. If I had to shoot a open choke .410 hunting, I would leave it at home, period. Like you I like choke and am not afraid of it in the .410 which is why I figured you were so concerned with convergence and POI in your guns earlier. If I wanted a big ass pattern I'd bring a 12. I find tight chokes, in a .410 are more workable, than many think. It is all about knowing where your POI is, getting a decent pattern density, with a workable size pattern.
You don't get good 20-24" wide .410 patterns, even with a 3" shell. Too much center density or the pattern just is too weak every where. Again with the trade offs. 2 1/2" ammo can give you 15-18" patterns with with enough density, you might get a little more with your 3" shell's heavier payload, but I have not had that much success getting that much of a wider pattern, without loosing center density.
A 3" shell, in a Skeet choke is not the answer. Been there and tried that. I think you have to drive that 11/16 or 3/4 ounce payload faster than 1125-1150 fps, in a tighter choke, than you are doing. With 300-mp, Remington hulls, Remington SP410 wads you might be able to do it but more likely at 11/16 than 3/4. But there is no published data so you need to create your own. I have loaded several loads in the past and had them pressure and velocity tested. If you are into uncharted loads, test ones both high and low, once you know the pressure is in a safe range you can try multiple loads in between, knowing you are safe. Then it is more about patterns, than velocity, after a point.
I've loaded 2 1/2", 1/2 ounce loads, which chronograph at almost 1425 fps. The patterns got better, when I backed them down into the 1250-1275 fps range but went bad again (too much center density) much below 1200, (1225-1150). I call it the sweet spot of velocity. I suspect you might get a 11/16 ounce, 3" load to push 1250 fps, without too much pressure and a decent pattern. I don't know if you can with a 3/4 ounce load. If not you best load is your best load, even if it is not what you set out to load.
