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Old 12-15-2015, 11:26 AM
crazyjz crazyjz is offline
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Default S&W M&P15-22 firing pin spring

I recently picked up a brand new 15-22 specifically so I could play with the "SlideFire" stock. I purchased the rifle, the SF stock, the CMC trigger assy. and after a while, the muzzle brake made by Wheaton Arms.

With only the SF stock and CMC trigger installed, I had immediate but limited success. I was often able to shoot a half magazine before some sort of malfunction stopped everything up. Mostly failure to ignite caused by light firing pin strikes but also some failure to eject and failure to feed issues.

I disassembled the rifle, polished up the feed ramp and took the razor sharp edges off of the actual chamber. The sharp edge would sometimes catch the soft lead tip of some of the rounds as they were making the transition from the magazine to the chamber. Put it back together and things went a little smoother with no further FTE or FTfeed issues. Still had constant failure to fire problems. At least one failure to fire per mag, sometimes two or three per mag. No good.

Inspection of the rounds that failed to ignite showed a very light firing pin strike. Bummer. I thought the CMC trigger was supposed to take care of that?

After reading several hours of opinions on the internet ranging from the scientific purpose of each aspect of firing pins springs, to those throwing caution to the wind and snipping off a bit of the stock firing pin spring, I made my choice.

Having been around firearms most of my life, I determined that the worst thing that could happen if I ruined my stock firing pin spring is that I would have to get another. No big deal.

I took the bolt assy apart. (By the way, all the advice about the ****** roll pin in the bolt is true! Either don't take it all the way out or have a new one on hand. They are cheap and soft!)

I clipped exactly 1/8" off of the firing pin spring, cleaned the pin and the channel and put it back together. I put the cut end of the spring on the pin and left the "flat" end to ride in the bolts firing pin channel.

My "reverse" muzzle brake arrived in the mail while all this was going on but I resisted the urge to install it prior to testing my firing pin spring modification. The firing pin still protruded out of the bolt as always but when pushed in with a finger or pencil eraser, it did seem to take less pressure to move it forward. I was beginning to doubt that trimming such a small amount of length off of the FP spring would do anything.

I loaded up two S&W 25rd mags up with elcheapo Winchester white box rounds. Went through both mags without a hitch! First time that has happened since I put the rifle together!

I installed the muzzle brake and went through two more mags without issue. I cannot say that the muzzle brake is essential in making the slide fire function but I don't think it hurts.

I am not advocating anybody do anything to any firearm. Risky business. I am only documenting what I did and the results I experienced.

Only time will tell if my FP spring modification will come back to bite me or if it was the right thing to do under the circumstances.

I do plan to contact CMC and see what they have to say about it. I did not have any FTFire's with the stock trigger assy. The stock trigger assembly is largely a piece of junk with a trigger pull so heavy that I could not activate the trigger with my trigger pull gauge. I guess the heavy springs they used is the reason I did not have any problems with the stock trigger.

I really like this rifle now!
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