What would I have to do to a .45 slidestop to have it function reliably in a .38 Super?
There is a lug on the inside/rear of the slide stop that goes through a slot in the frame and engages the magazine follower when the magazine is empty. But it has to be shaped so that it doesn't touch the nose of a bullet as the cartridges feed up through the magazine. Otherwise the slide may lock back before the last shot is fired. The shape of this lug (in theory) is slightly different between a .45 and .38 Super.
If for some reason you need to use a .45 slide stop, field strip the gun and put the new slide stop back into the frame. Insert a loaded magazine and push the cartridges out of it with your thumb while watching to see if the slide stop moves up. Then see if, after the last round, it engages the magazine follower and is pushed up as it should be.
I think there is one thing for sure, a 45 slide stop in a 38 Super will not contact a bullet in the magazine and prematurely lock the slide! In fact, the lug may be so short that it will not reliably engage the tab on the magazine. Your best bet is to buy a slide stop designed for the 38 Super/9mm.
While I would agree that it would be best to buy a 38 Super slide stop, I would also point out that the .45 and .38 Super magazines are both the same width. The 38 magazine is ribbed on the sides to center the smaller cartridge, but a ,45 slide stop should be able to reach the tab on the front of the follower.
I used 38 Super slide stops in all the .45's that I built. They are better at locking the slide back and are not prone to have a premature slide stop failure with hardball. I fitted every part in those days and that was one I had no trouble with ever. They do reach in a little further and work better with hardball or semi-wadcutterts.
Quote:
The 38 magazine is ribbed on the sides to center the smaller cartridge, but
a .45 slide stop should be able to reach the tab on the front of the
follower.
Not on Mecgars. I have a 1911 combo that has both a 9mm and .40 top end. I use a 45 slide stop and the followers in the Mecgar 9mm mags would not operate it (had to bend the foot on the follower). The CMC mags in .38S did work as is.