Arguably for the air cushion.
We ring steel. We don't kill it nor do we want to bend or punch holes. Limitations on handgun velocity show that. The trick that all competitors look for is the ultimate load. I guess we are gamers
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I shoot 105gr ltcfp with 3.2 gr of American Select. 795 fps out of the 3 screw's 4 5/8" barrel. 38 Special brass. That same load in a 357 Mag case would provide velocity loss and a longer recoil impulse that translates to less felt recoil. You have to be aware that we are in a gunfight. We are not pinned down behind a dead horse shooting bad guys at 200 yards. Shades of Lonesome Dove.
Our scenarios usually dictate that we fire ten pistol rounds, ten rifle rounds, and four shotgun rounds. With a little movement, that is, running to your rifle after you have fired both pistols, and running to your shotgun, this stage should be shot by the very good shooters in about 20 seconds. Little recoil, swift recovery, and fast shooting.
Some simply like to fill up the chamber since most of our revolvers are chambered for 357s. In the last ten years, my 3 screws have never seen a Mag round.