View Full Version : AR-15 issue

July 22, 2012, 01:44 PM
Hello all,

I've got a rather serious problem with my Bushmaster XM-15. For some reason, the rear takedown pin is no longer captive. Turning the rifle to its right side will very likely result in the pin just falling out, sometimes even if the turn is very gentle. Obviously, I don't really feel inclined to shoot it in this state.

I've done a bit of research, and have come across items such as this one (http://www.cheaperthandirt.com/product/ARR-360) that, if I'm not mistaken, could possibly remedy this issue. For the life of me, I have no idea why the pin has ceased to hold. I've had the gun for about eight years, but just experienced the problem recently. Any advice or input is greatly appreciated.

July 22, 2012, 01:48 PM
have you considered just buying a 5 dollar take down pin? you don't need anything fancy and for the most part they are universal.
one of the related items on your link is this (http://www.cheaperthandirt.com/product/ARR-323)
it is a set of DPMS lower pins, DMPS and bushmaster are both owned by cerberus and both use the same parts.

July 22, 2012, 01:53 PM
The takedown pin is retained by a detent and detent spring that are held captive by the buttstock.

The detent and detent spring are only a couple dollars each.

July 22, 2012, 01:53 PM
Have you had the receiver end plate off recently? Because you are missing your rear takedown pin detent and spring.

(Item 110 & 111)


July 22, 2012, 02:02 PM
Skadoosh - nice job with the diagram!! :D

July 22, 2012, 02:34 PM
With a problem like your having there is only one thing you can do. Use this OPPORTUNITY to explain to the wife why you have to get a new AR!:cool:

July 22, 2012, 02:39 PM
Thanks, for the feedback, everyone.

I haven't had the receiver plate off recently, so I'm not sure if it is missing the pin detent or not. My adjustable stock is fixed in with a nut that I need some sort of allen wrench to remove though I can't find one that fits in my meager tool collection.

Would purchasing one of those push button takedown pins be likely to solve the problem?

July 22, 2012, 03:53 PM
Take this as an opportunity to learn how to disassemble that portion of the rifle. It is a simple spring/detent replacement.

July 22, 2012, 04:09 PM
First I'll have to find a wrench to loosen the lug stock so that I can remove it, which should be its own kind of hassle. Hopefully I can find a properly sized allen wrench.

Edit: I'm referring nut under the lever you pull to slide the stock back. The thing WILL NOT budge so far.

July 22, 2012, 04:20 PM
Are you referring to the castle nut?:


If so, you need to realize that it has been 'staked' which can be seen in the picture above. Staking ensures the nut will not un-thread itself because of vibration. You will need to purchase a AR/M4 castle nut wrench.

Or do you have a Bushmaster with an A2 stock?

July 22, 2012, 07:37 PM

July 22, 2012, 09:29 PM
Chances are you lost the detent when the takedown pin pulled out. The best insurance is to get a couple spare detents and springs.
Castle nut wrench $9 (http://www.midwayusa.com/product/154145/tapco-multi-tool-ar-15-mil-spec-steel?cm_vc=Sub_1)
Takedown detents $2 (http://www.midwayusa.com/find?sortby=1&itemsperpage=100&newcategorydimensionid=9738&)
Detent springs $2 (http://www.midwayusa.com/find?sortby=1&itemsperpage=100&newcategorydimensionid=9739&)
Takedown pins $4 (http://www.midwayusa.com/find?sortby=1&itemsperpage=100&newcategorydimensionid=9740&)

Instructions with pictures can be found at the link below.
Assemble your AR-15 (http://www.ar15.com/forums/t_3_4/226782_Assemble_your_own_LOWER__UPPER__FREE_FLOAT__TRIGGER__GAS_BLOCK___Step_by_step_instructions_.html&page=1#i1847394)

For an instructional video, click the link below.
Video on collapsible stock (http://www.youtube.com/watch?v=1P00gGNkjqQ)

July 22, 2012, 09:45 PM
Desert fox, forget a special Allen wrench. If you pull it down further than the stroke of the lever you should be able to slide the stock off the back of the buffer tube.

July 23, 2012, 05:53 PM
Sounds to me like we may have broken the detent hole out of the lower while pushing, pulling, or whacking the takedown pin. Pull the upper and look inside the lower where the rear pin goes through and see if there's a little chunk broken out of the side of the lower where the detent should be. Believe it or not, I saw a guy who had taken a punch and driven the takedown pin completely out of the lower ruining the lower in the process.