3/4 factory ammo will often be loaded at a high pressure to operate semi autos. If you look at Hodgdon website 3/4 ounce, pushing 1200 fps are often 10,000+psi some much higher. We do not know what factory shells like Winchester, Remington or even Federals pressure levels are. But they all operate semis so most likely higher than what we want.
If you reload things get easier since RST seems very limited in production these days. I trim my hulls to 66-67mm which are acceptable for 2 1/2” chambers. I load mostly 572 because they both work well and are available. At my Sporting range I can pickup all the Federal, Cheddites and Fiocchi 20 gauge hulls I want for free. Federal hulls run 7,000-7,500 for 1150fps. Bump it to 1200 and you are still well under 9,000psi. Stack height works well. You can find loads for the others using the same powder. To keep things simple only 1150/7,500 loads go into Federals, 1200/8,500 go into Cheddite and 1150/8,500 go into Fiocchi hulls. High pressure loads only go into Remington and AA. Plus free hulls can be single use hulls if needed, they were free.
