Couple of thoughts. SAA ignition system consists of four parts that work in unison or should, trigger (which is actually the sear), the hammer, main spring and sear/bolt spring.
Sear on a
new USFA part (don't have a set of Colt parts handy enough) is .030"+/-. But that # gets cut down anyway. Hammer hooks on a
new hammer I have here are .029/.030". (Colt hammers run .030 to .040" by spec.) Spring can be anything from stout flat springs to wimpy piano wire depending on what you like. Never seen this on a Colt for sure. But the internal radius is the same or should be I believe @ 48.5 degrees.
(this turned out to be the key)
Assuming trigger and hammer contour is correctly mated/matching (on this gun my guess would be this tolerance/clearance is simply too tight) keeping the trigger from coming back to the fired position just a millisecond later with a lighter spring might-change the feel of the gun.
I'm only guessing. But do know the lighter weight trigger/bolt spring eliminated much of the "slap". But still 5% of it I could feel if I was dry firing the gun. Not much but the problem was not totally solved just as Rifle suspected and others have also noted, it likely didn't eliminate the problem.
So a few moments ago (between paragraphs actually) I tore the gun apart again. Now I went looking for contact on the back of the trigger and the curve of the hammer under the hammer hook/sear engagement. No obvious contact there. So I then checked the hammer and sear mating radius.
Bingo! Back of the trigger contour was not cut with enough clearance behind the screw hole. Obvious when I pulled out some new Colt triggers and a few more new USFA triggers. Easy to fix. 5 minutes may be. Easy enough to miss if you were building the gun from scratch and a parts bin.
As I said. only ever felt two guns do it. Both USFA. Now I'd guess they both simply had out of spec triggers installed.
My thanks to Rifle who admitted he had not seen such a thing and then proceeded to think it all through anyway... and still came away puzzled Your comments were much appreciated. Nice bit of critical thinking on your part. Thanks for writing it all down. Got me to rethink it all as well. Took me longer to type this than fix the gun