Rear takedown pin loose and keeps sliding out

[Cool-AR15]

The rear takedown pin on my 556 pistol is extremely loose. It will just slide out when picking up the gun. The gun is new and has only been to the range a few times. The pin is dry with no oil on it but it still just slides right out. Any advice?

[sigforever]

Sounds like the spring and pin that applies pressure to the takedown pin is absent. Did you remove or change the stock in any way. You might have accidentally lost the spring/pin combo. Ryan

[Wabbit]

+1 on Ryan. Also, older model 556 have two small AR sized pins in there. They later came out with one long one. So if you think you only had one small pin, you probably lost the other one.

[Cool-AR15]

Here is a picture of the the rear takedown pin. It's hard to see from the crappy picture but the groove in the pin is empty. Should there be a spring in that groove?
Also is there a special tool to tighten the end cap? For some reason that is loose.
Thanks.

[/img]

[Wabbit]

You won't see anything in the groove, that is where the pin rides. Since your butt plate is loose, you may have lost the pin and spring, or it could just be a matter of tightening the plate. You can order the pin and spring from Sig, I'm sure. I'll have to take a look at how the butt plate attaches and get back to you.

[enigma]

good remote diagnosis! I would concur on the rear spring theory.... I have lost several of them, and more than I could count on AR platforms. It is one of my FEW peeves with the 556 platfrom the use of the same darned pin and springs on the lower as are used on the AR. The small consulation prize is I suppose that it is easily replaced with AR spring and pins, and they can be found at gun shows cheap enough.
One good solution if the replacement of the standard rear pin with a Swiss style takedown pin... KNS makes a decent unit, and Colorado Gun sales has a U.S. manufactured clone of the real Swiss pen...

[Cool-AR15]

Thanks for the replies. I looked up the KNS pin and they just show it as a front pivot pin replacement. Has anyone used it as a rear pin if it fits?

I just found that they do make a rear pin.It shows it will fit AR's.
http://dynamicarmament.com/items/ar15-accessories/kns-precision~inc-/kns-take-down-pin-rear-detail.htm

[Wabbit]

The Sig 556 uses a long pin in the rear takedown, so a standard AR pin wouldn't be long enough. However, the older model Sigs used two small pins which looked very much like the pin used in AR's, so in a pinch you could probably get away with two standard AR pins.

I would not go with the KNS pin for the rear. I'm not sure the AR and Sig are the same width, and the capture pin is a better, easier to use design.

I am not sure how that butt cap on the P556 is tightened on. It looks like it needs some sort of specialized tool. I'll have to check on that.

[knsgordon]

The SIG 556 Pivot Pin from KNS will work in the rear take down. It is the same pin, not an AR15 pin. The SIG 556 Pivot Pin was developed to replace the factory two-headed screw. Plus, if you don't like it you can call me and I will make it right. Thanks!

[Cool-AR15]

[Cool-AR15]

[1sttexan]

One BIG OL rule. Unless it's a tooth or fish hook.NEVER use pliers to just yank it out!