I'm having the dead trigger issue with my 9c with the Apex Tactical DCAEK kit. I emailed Randy of Apex Tactical concerning this; Here is my email and his response:
"I have a M&P 9c that I recently purchased from G&R Tactical with the DCAEK installed. I am experiencing a frequent problem in which the trigger does not reset when released, and then is "dead" on the next shot."
His Response with price x'ed out:
"The dead trigger is related to sear bounce as the sear spring is just too small. Our fix is to install the larger MA style sear spring and plunger which is now being phased in by Smith on all new production guns. The larger spring is able to respond faster to the recoil impulse than the anemic spring setup. If you send us the sear housing block assembly, I can mill it for the larger sear spring and plunger. The cost is $x.00 for the new sear spring and plunger. Return shipping is $7.50 for priority mail. I will turn it around in a day. Let me know if this will work for you. -Randy
Hope this helps,
Trvlngnrs