FYI regarding using .303 British brass. It works but you end up with a lower capacity shell (in a bore which is already low capacity). The .303 never blows out completely.
Here is one next to a factory 2.5 inch.
Thanks for those articles. They are the best that I have read on the subject.
v So if you plan to create a 3-dram, 11⁄8-
ounce, 12-gauge load of 1,200 fps, for example, you might not need any- where near the called for amount of powder
An anecdote about this idea. I had loaded 25 RMC hulls with a standard Trap load....18 grs. Of Red Dot and 1 1/8oz of shot. I went to the Trap range and got into a squad. The shells worked just fine. About the time I was on Station 3, the range officer overseeing the shooting told me to stop because the shells that I was using were too powerful (evidently the report was louder). I told him what the load was but he insisted.
I finished with regular shells.