I have the 4.0" barreled 10mm. My recall is that the 4.6" version never had many complaints, and certainly fewer complaints than did the 4.0" version.

Anyway, I changed the recoil spring (based on early owners' input) and scrubbed it down thoroughly to be sure all of the packing grease was gone (another early owners' recommendation). I've had zero problems with it...from the first magazine until today, 2 years later.

My frustration was not being able to find additional magazines (same mags work in the 4.0 and 4.6 guns). That issue, too, is now resolved. So, I'm a happy camper. My 10mm is actually more fun to shoot than my 45 acp 4.0" M&P, although I like both of them. So now I have 4" guns in all 5 of my favorite calibers: 9 mm, 40 S&W (with a 357 SIG drop-in barrel), 10mm and 45 acp and like all of them. My only frustration is deciding which one(s) to take to the range each trip.