Sidearms & Scatterguns Help with M&P 45 and hot loads

[clmayfield]

I have run into some problems and I was hoping the pistoleers here could help me out. I have an M&P45 that has run pretty flawless (one FTE in 1,500 rounds) using light to moderate loads (200 gr lswc + 5.1 gr W231/HP38) as well as 230 gr hardball factory loads (which is moderate to heavy).

I have a bowling pin shoot coming up and have been working up some hot heavy loads... 250 gr rnfp + 5.6gr W231. I don't really like to run loads this heavy, but when I tried a moderately hot load in the last match, my hits were not clearing the pins (and they were pretty well placed).

Anyway, I found that every 5 rounds or so, I would pull the trigger and nothing would happen. I would release the trigger and pull back all the way and still nothing. Articulating the slight slightly without ejecting the chambered round was enough to get it to function. I was ejecting the brass all the way to Dallas, so I thought maybe the problem was that the slide was moving too fast, so I bought some extra power springs from Wolff and an aftermarket guide rod. Same problem today with the heavier spring. This is a 22 pound spring. They sell a 24 pounder I guess I could try, but I get the feeling that might not do it as the brass seems to be ejecting right where it used to (with the moderate loads).

This load is working fine in my 1911 with an extra power spring, so I am trying to imagine what is going on here. It seems that if the striker were not resetting, I would be getting slam fires, so it must be the striker block is not resetting? Why? Anyone aver heard of this or have any ideas?

Thanks!

 

[rjacobs]

Sear bounce. The M&P's are known for it, especially with hot loads. Although the .45 isnt known so much for it, but I would say it could still happen because it shares the same basic design as the 9 and 40, but generally the .45 is a much gentler round than 9 and 40 so it doesnt exhibit the issue as much. I would call Randy at Apex and see what he has to say as they have solved almost all of the factory short comings that the M&P's have.

 

[Gunfighting Inc]

Sear bounce. The M&P's are known for it, especially with hot loads. Although the .45 isnt known so much for it, but I would say it could still happen because it shares the same basic design as the 9 and 40, but generally the .45 is a much gentler round than 9 and 40 so it doesnt exhibit the issue as much. I would call Randy at Apex and see what he has to say as they have solved almost all of the factory short comings that the M&P's have.

^^^+1. How old is your pistol? Older models had a smaller sear plunger and spring. Newer models are much larger to solve this issue. Randy at Apex does a retro fix.

 

[clmayfield]

Thanks! I have been researching it and it looks like I have sear flutter. I remember the plunger being the small style despite being a new pistol.

 

[rjacobs]

If you have the small style contact Randy since I dont think you can get the new style from S&W anymore. Randy can drill out your sear plunger spring hole for the newer larger one for like $25 and fit the new sear spring and plunger into it from their kit. Will solve all your issue's IMO.

 

[clmayfield]

I called Apex. I have adjusted all of the pretravel out of the trigger. He thinks that because of that fact, the extra recoil of the heavy loads are causing me to let off before the trigger has a chance to reset. I will try that and let y'all know.

He said (based on date of manufacture) he is 99% that the plunger on this thing is the new version... but I will need to pull out the calipers to be sure.

It sucks because I spent a while adjusting the trigger to have zero takeup. For reliability's sake, I will need to add a little pre-travel.