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Old 12-16-2015, 09:13 PM
crazyjz crazyjz is offline
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Default M&P 15-22 slide fire firing pin and spring mod

Ok, I know that I am well behind on the popularity of the S&W 15-22. I just did get the bug and have found myself scouring old posts looking for info on various slide fire modifications necessary to get the rifle running right.

The obvious purchases aside, CMC trigger assy., reverse muzzle brake and of course, the SlideFire stock itself, there are a few other minor modifications necessary to get some of these rifles cooking properly.

Of course, somebody will chime in here that their 15-22 came perfect from the factory and they have shot 1 million rounds through their rifle, shooting nothing but wooden bullets, wearing a blindfold, without a stumble. If you're that guy, I have nothing for you.

If on the other hand, you have purchased all these parts, got close to a grand invested and the damn thing still does not rock and roll like all those guys in the "YOUTUBE" videos, read on.

I am an amateur gunsmith. That's right. One of those guys who tinker around with stuff that they know little or nothing about. On the other hand, I have been doing it for about 30 years so I have managed to pick up a few things along the way. With my 15-22 totally decked out with all its new parts, I was still having failure to fire problems. Inspection of the failed round showed an almost invisible firing pin strike mark.

A search of the internet revealed that installation of lighter trigger pull kits often results in light firing pin strikes. Damn, nobody told me about this! Ok, no big deal. I'm sure I can figure this out.

An inspection of the firing pin and firing pin spring revealed a very substantial spring. The internet consensus is that the FP spring could likely be the culprit for light FP strikes. Since I know I can always replace the factory spring, I cut 1/8" off the spring. Testing revealed very little difference in the depth of firing pin strike marks on fired brass. A check of the firing pin itself revealed that at full forward position (simulated by pushing the base of the firing pin forward with a punch) the firing pin was only protruding about half what it should have been. Damn, no wonder. But why? Back to the internet.

Ok, I give, seems like the only way to allow more of the firing pin to protrude through the hole to strike the case is to file off a little bit of the slot in the firing pin. By the slot, I mean the portion of the firing pin that is milled away where the roll pin holds it in place. This milled away area directly relates to how far forward and how far rearward the firing pin can travel during a single bolt cycle. I took a small chain saw file and removed about 2 or 3 thousandths off of each side. I then buffed it smooth and reinstalled. This time the firing pin protruded out the bolt further but not to far. It also seemed a little easier to push in on.

I buffed everything that rubbed up on anything, put it all together and it worked. Go figure. I now have completely respectable firing pin marks on all my brass whether firing slide fire or not.

Last but not least and I'm not sure it even matters but I also made a modification to my slide fire stock. I have the MagPul style of 15-22. It came with some sort of quick release sling stud on the stock. This stud interferes with the full and complete operation of the slide fire stock. I simply notched out a couple of semicircles where the stock was hitting. Now I have total front to rear movement of the stock. Don't know if it was bothering anything besides me but now its fixed.

Thats it. Sorry for the mega long post but I wish I would have run across a few more posts like mine to help me on my way to dialing in my 15-22. It would have given me a bit more nerve in modifying some of these parts!

I do not recommend anyone do these things to their rifle. Guns are dangerous enough without changing the way they were intended to work. I only document this to show what I have done to my rifle and the results that I experienced.
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