Too lazy to find the gauge, but I ended up with Apex "Carry" kits on two M&P40's - one FS and one Compact. The Compact is superb this way (and the trigger pull is indeed somewhat reduced). The FS needs a little more lubrication & such, but still helped out.
S&W should buy Apex (
) and supply the guns with this kit installed.
(The kit's pretty simple, but you do want a roll pin punch, and the sear return spring is
extremely tiny, as is the plunger. I have no idea why I didn't manage to lose the plunger....)
Regards,