I wish I still had some 6-1/2s left. They ran pretty well in most things, a few of the really light revolvers had trouble but autoloaders digested them very well indeed. I think I ran about three bricks through pistols and fed the rest to my M-1 carbines.

I’ve used magnum primers in place of normal primers with no ill effects.
I’ve used thousands of small rifle primers in handguns, some Fiocchi, CCI, and several thousand Federal.
I’ve have very few primers that didn’t run fine in autopistols. Most guns they seem to run 100%, but I have a couple that had about a 1% failure rate with the Federal 7-1/2s, a re-strike usually set them off.
Revolvers are a lot more mixed. Some will not run the Federals al all, others will run them about 75%-85%. The 6-1/2 are clearly easier to set off than the 7-1/2 but some revolvers won’t even run those.