Need help with Detent spring and Detent pin issues!!!!

[browningboy84]

Ok,

I have a S&W M&P 15 AR. I bought it back in November of 2008, it is a flat top. Round Count is between 800-1000 rounds, tops. I have had issues with it lately chopping up the buffer detent spring, and the buffer detent pin is coming out and laying loose in either the upper or lower when I dissasemble the gun. I have bought 2 replacement pins and springs from Brownells, Colt and DPMS. Both of them had the same thing happen, it chops them up. It bent the DPMS spring, and chopped the Colt spring in two, literally. I dont have the Colt springs anymore, they got lost the other night, but I could use some help on this. The only mods to the gun that I have done from factory is a MagPul trigger guard, and a Single Point Attachment. The castle nut is locked tight and there is no play in the buffer tube. Any help on this would be appreciated. I am gonna call S&W tomorrow, and see what they have to say, but I am at a loss as to what the F@$% is going on. Thanks in advance.

[az doug]

Which detent and spring? From your post I believe it is either the buffer detent and spring or the rear take down pin detent and spring.

If it is the buffer detent it could be the receiver extension tube was not turned in far enough if your single point attachment required you to replace the "receiver extension plate."

[browningboy84]

Which detent and spring? From your post I believe it is either the buffer detent and spring or the rear take down pin detent and spring.

If it is the buffer detent it could be the receiver extension tube was not turned in far enough if your single point attachment required you to replace the "receiver extension plate."



Buffer detent spring and buffer detent pin. Post clarified also

[az doug]

That is generally a sign that the receiver extension tube was not screwed in far enough. The tube can be screwed in to a point that it barely retains the detent. During cycling the buffer strikes the back of the extension tube forcing it slightly backwards. This slight movement allows the detent to "pop up" in front of the bolt carrier. As the bolt carrier cycles forward it stikes the detent shearing it and possibly the spring.

One cure is to tighten the extension tube in to the point it touches what you refer to as the "pin" on the detent and if it does not line up at this point, which it probably won't, back it out just far enough for the extension tube, stock and receiver plate to line up properly.

Another cure is to notch the bottom of the extension tube so you can turn it in one more full turn. The bottom of the tube then encompasses the sides and back of the detent allowing the "pin" to stick up through the tube.

Hope this helps.

Doug

[Chuck TX]

Sounds like the receiver extension should have been turned in once more.

[browningboy84]

When I get back home Thursday morning, I will see what I can do. Hopefully that will fix the problem.

[dcs12345]

Sounds like the receiver extension should have been turned in once more.

That is what it sounds like to me as well.

The buffer retainer should be held down by the edge of the receiver extension. Back off your castle nut and end plate (watch out for the rear takedown pin spring under the end plate) and turn your receiver extention tube until it captures the buffer retainer. ..