Many years ago I used a pack of small rifle primers to load some .38 Special cartridges. As I was cleaning up and putting things away I discovered the mistake. Wanting to take no chances with my S&Ws, I asked a friend to test a few in his Ruger .357.

After firing a few in the Blackhawk, we tried them in my K38. No problems. Like the OP, since then I have tested small rifle primers in .38s in various guns, and over the chronograph, and never had the first failure to fire, or any other problems.

In my case, the primers were Federal 205s. I can't give advice on this to others but I will say that since that "discovery" I have never hesitated to keep a few thousand more small rifle primers around than I think I might need for rifle shooting.