I've been intermittently having the same problem.
I had a long talk today with a gunsmith who frequents this forum (I won't say which, since he didn't give me permission to share our discussion). He made some interesting points:
1) This is most likely shooter-induced. It's OK, I"m a big boy and willing to admit it might be me.
He said that since the .40S&W round is so "flippy" - that is it tends to muzzle flip worse than other rounds - that he sees this problem a whole lot more in .40 caliber than any other. Apparently under recoil, my hand may be brushing against the slide lock lever. However, this leads directly to point #2.....
2) If the change in my grip technique is going to be such that I need to microscopically adjust this finger or that one just a millimeter here or there, or hold my tongue just right, or whatever, then maybe this isn't a good gun for my personal CCW. If I'm in a rainy Wal-Mart parking lot some night and get jumped will I have a chance to take ten seconds and make sure my grip is perfect before I fire?
3) He suggested maybe I consider trading my 40c for a 9c. And I'm willing to do that if that's my best option. However, I also like having the biggest bullet I can. As the FBI study on the subject says, among bullets that penetrate adequately, the edge goes to the bigger bullet.
4) I'm wondering if the new .45c might be a better option. I've never seemed to have a problem with .45 in other guns, since these seem to be more of a strong "push' in recoil that an explosive "flip." (Hope I don't lose anybody in my technical jargon here :wink: ) I know some will question why I would want to move up in caliber since I apparently can't "handle" a .40. It's not the recoil that seems to be a problem, but rather the "snappy" character of the .40. I used to shoot .357's regularly, so recoil doesn't bother me much.
I've sent the gun to S&W three times. They replaced the slide lever spring, but the problem remains. I'm beginning to think it might be me.
Anyone have any thoughts on my 9mm vs .40 vs .45 dilemma? I'm not looking for another debate on various calibers. I understand that a bigger bullet is better and shot placement is key. What I'm wondering about is if the .45c has less muzzle flip than a .40c. Specifically, I'm wondering if a .45c would be an equally satisfactory choice over the 9mm to resolve my early slide lock issue.
Any other possible suggestions on resolving my early slide lock issue is welcome. When I get a change, I'm going to go shoot at the helpful gunsmith's place and see if he can come up with a solution for me. But I always like to explore all options!