Stupid AR .308! Geeeze, now what?

[gun'sRgood]

You guys were trying to help me find out what's causing this AR .308 to not fire. I had thought all along that the upper was the issue. Now, I have put a different lower with all the parts I had for the original lower. It fires fine. I traded out the parts into the new lower and it fires fine. So, What's in the original lower that's keeping it from functioning? In both of these lowers there is a set screw under the rear take down pin. I'm not 100% sure but it seems to be there to help secure the upper to the lower? In AR 15's, I just put in those little spacers. Anyway, Ideas?

 

[Blue68f100]

In both of these lowers there is a set screw under the rear take down pin. I'm not 100% sure but it seems to be there to help secure the upper to the lower?

Could be the retainer to hold the spring for the detent in the pin.

I never use spacers, not needed since the optics/sights are all on the upper.

As far as the original lower not working it may be tolerance stacking. This happens when one is at min the other is as max. I know when I went to machine my 80% lower specs were all over the map. I spent more time digging for the correct one than it did to drill the holes.

 

[Armorer 101]

If it is what I think it is, based on the description, you can put the upper on, then use a long allen wrench inside the pistol grip screw to fit the inside allen head screw, it should turn in tight to lock the upper down tight. To remove the upper, just loosen the screw and remove the takedown pin. You can shoot the gun without the screw being tight. It is along the same idea as the wedge, just a screw set.

 

[gun'sRgood]

If it is what I think it is, based on the description, you can put the upper on, then use a long allen wrench inside the pistol grip screw to fit the inside allen head screw, it should turn in tight to lock the upper down tight. To remove the upper, just loosen the screw and remove the takedown pin. You can shoot the gun without the screw being tight. It is along the same idea as the wedge, just a screw set.

Thx. I'm hoping that that pushes the hammer forward a bit and starts to work. Thx

 

[mpofficer31a]

It's very hard to help with the information you provided... What brands and type are each lower? What brand and type is the upper? (For example Palmetto State has a Gen3 AR 308 that doesn't seem to be fully compatible with a LR308/SR-25 style rifle.)

Overall, the set screw under the rear take down pin shouldn't affect function; if that screw is set too high, the upper won't set into the lower enough to push the pin through. If the pin will go fully into place, I doubt the tension between the upper and lover would affect functioning much, or at all.

Can you give us a few more details about what it was or was not doing that seemed to keep the first lower from functioning?