Hello All, I purchased a police trade in M&P .40 that is in almost new condition. I would like to install a Apex Action Enhancement Trigger Kit for M&P. However, the Apex site advises the following: This kit REQUIRES the use of the larger 1/8 inch sear spring and plunger set up. If your M&P has a 1/16th inch diameter sear plunger and spring, we strongly advise you upgrade to a new style sear housing block before installing this product. Can anyone tell me how to tell if I have the 1/8 inch spring and plunger? I have installed Apex triggers before but I am unsure of what to check or measure. Thank you in advance.

Call S&W and ask when your MP was made. Then ask them which sear and spring size it has. DON'T tell them you want this info. to change things with your MP.

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How many guns are too many?

OR, you can simply take your sear housing apart and see what size drill fits in the sear spring hole.

IMG_0039_zps29aea7bf.jpg

Great idea!
But, if you call S&W you can get the size AND when the gun was made.

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How many guns are too many?

Original style sear plunger & spring on left. Revised (larger) on right.





The older and newer sear blocks aren't interchangeable, though, depending on the way the outside guide rail (front/left?) of the sear housing block was shaped (and the frame molded to accept it). There was a change at one point which would mean the newest blocks wouldn't fit inside the older frame because the a rail guide wouldn't match the frame.

FWIW, one of the things that bumped up the trigger pull weight in the original MA complaint M&P's was the original use of the large sear plunger spring & spring (when the standard plunger and spring in the rest of the models were the smaller ones). The other things that added to the trigger pull weight in the MA models, if I remember right, was a steeper angle of the "candy cane" trigger bar's cam surface, and a heavier trigger spring.

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Ret LE Firearms inst & armorer