Rear Recieiver Pin Question

next mayor · Nov 11, 2011

Was just wondering if anyone had any issues with their rear receiver pin?

While mine has never fallen out, at least once per visit to the range (200-300 rounds) I seem to catch this pin on the verge of falling out.

This rifle is far from abused and I am the only owner. If I had to guess, I say I've only got 1000-1200 round through it.

Any opinions on if I got a problem, bum receiver pin, or just a normal issue?

Thanks.

P.S. Guess I can't spell receiver.

ragingyeti · Nov 11, 2011

Have you replaced your pistol grip? If you did, are you sure you put the takedown pin detent and spring back in? If the detent isn't in there, that would explain why the pin is walking out on you.

next mayor · Nov 11, 2011

yes, replaced grip. I thought I had it all together correctly. Will take a look tonite and see what's going on.

next mayor · Nov 11, 2011

Called S&W and they are sending me a couple for free. Not sure if they are currently in place or not, but can't hurt to have them. Thanks.

ragingyeti · Nov 11, 2011

Let us know. If your detent and spring are in place, then we need to find the real problem. Can't have the rifle falling apart when you are shooting it.

Hobie1 · Nov 11, 2011

One other thing about the pin...make sure the pointed end goes in the hole first. Sure is a tiny lil' thing. Make sure your bench and floor are clean before taking the grip off. Ask me why I know.

Hobie

chuck s · Nov 12, 2011

Those familiar with the M16/M4/AR15 will be surprised to find two springs and detents under the M&P15-22 grip. The springs will be pretty obvious but the little detents can fall out undetected and they take a sharp eye to find after they've bounced across your basement floor. (Who, me?

)

The M16's rear takedown pin spring and detent are secured by the stock or receiver end plate on the carbine versions, hence the surprise many of us get removing the M&P15-22 grip.

-- Chuck

next mayor · Nov 12, 2011

Okay, I just took a look and a spring loaded brass (looking) pin is in place in my rear receiver whole. When pressed, it does spring back up, and there is a noticable resistance when the pin engages the groves on the receiver pin. However, that resistance is very very weak, nothing at all like the front pin. FYI, it looks like the point / rounded end of the pin is what is engaging the pin.

So what now? Any ideas? Should i try to find a stiffer spring for the pin?

Also, has anyone found a parts diagram online anywhere?

Thanks all!

Hobie1 · Nov 12, 2011

Have you tried turning the pin end for end?

I'll be curious why this problem has developed.

Hobie

Gopher Slayer · Nov 12, 2011

What kind of grip is it? Could the hole that the spring rides in be too deep? That would be an easy fix.

Also, make sure the spring went in correctly from when you changed grips. Mine started kinking when I was trying to get everything lined up to tighten down the grip. I finally got it and it works great.

ragingyeti · Nov 12, 2011

I think Chuck and Gopher slayer are on the money here. I feel it is the grip that is the issue. As Chuck already stated, with a standard AR15 the rear takedown pin detent and spring arel secured by the end plate, as in this picture where the red line is (the yellow line is the safety selector detent and spring):

However, on the M&P 15-22, the takedown pin detent and spring are held in place by the pistol grip, as seen here in the red circle (again, yellow is for the selector detent and spring:

On a standard A2 pistol grip, there is a lip at the top that will actually hold the rear takedown detent spring in place.

However, since this spring is somewhere else on an AR15, some AR15 grips do not have material in this spot. This would cause the spring to not be held tight enough for the detent to work. Here is my MOE for example:

The MOE still works however because there is enough of a lip so that half of the spring is touching, and therefore retained in the lower receiver.

If your pistol grip doesn't have enough material to catch the spring in this area, the spring won't provide enough pressure to properly function the detent. It is also possible that the spring is pinched under the grip. I would just observe if the spring is being pushed into the receiver by the grip as you put it on. If it isn't, this could be the problem.

next mayor · Nov 12, 2011

Will look now, but it's either a MIAD or MOE. Will try a couple of things. Thanks for the pics. And thanks to all for the help.

Gopher Slayer · Nov 12, 2011

If it's a MIAD, that's definitely the problem. I know a quick fix for that too.

The MIAD doesn't have that lip like the MOE in raginyeti's pics. I have one on my 15-22.

next mayor · Nov 12, 2011

Thanks guys, the pics were a big help. I've got a MOE grip and the small detent spring wasn't seated right. While reinstalling the grip, i made sure the spring stayed in place and the pin is a lot more secure now. Thanks all.

ragingyeti · Nov 12, 2011

I'm glad I could help and we got it all squared away. Happy shooting!

next mayor · Nov 12, 2011

Going shooting tuesday nite. Will keep you posted. In addition to the receiver pin, i did some other very minor adjustments to my 15-22. It's just about completely dialed in for me.

tacticool22 · Nov 12, 2011

Almost done... Until the next thing;D

chuck s · Nov 13, 2011

I was about ready to start a detailed message when I scrolled thru Ragingyeti's phoso essay. Well done!

-- Chuck

Rear Recieiver Pin Question

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