I found the problem.
Too little crimp. I was using 3.6 Win 231 with a Moly coated lead 147 grain TC. My source for the load was the 48th edition of the Lyman Reloading manual. I use data for 147 grain jacketed, started low and worked up. I also have older manuals giving 3.5 as max. Also queried on this forum.
I shot last night in a practice session at our gun club. This time I paid attention to what was happening to the bullets. The bullets were moving forward and coming loose from the case. The magazine would hold them and would feed.
But when I removed the magazine and cleared the pistol the top bullet in the magazine fell out.
The beginning round in a mag would be loud but as the bullets loosened some of the later rounds would almost sound like squibs. I won't know for sure until I re-crimp and test fire them. I will post the results.
Thanks again for replies. Power Pistol and WSF are on my list to try out.