I've got a pre ban cast DPMS lower and a new DPMS M4 type upper that I'm trying to mate.  The takedown pin won't go through the hole.  Front one is smooth but the rear is a no go.  I've tried tapping it and it goes about half way but not without a fight.  I've never had one this difficult before and am curious if anyone has had similar trouble and found a solution...???

John

One of two choices,

The first is to send the upper and lower off to DPMS and they will swap the upper to one that matches the lower.

The second is to just use a small round file (jewelers) and just take a few strokes out of the upper lughole to allow the two to mate. Since the pin will fit half way, it would only take a few strokes to clean up the hole.

Take down pins are cheap and easily replaced. I'd take the pin out and try it in the upper alone.Fit's ok and you have a alignment problem between the upper and lower.Maybe just a little anodizing irregularity.Use the takedown pin to lap the bore of the pinhole in the upper.Maybe bevel the very tip of the pin very slightly.Is the takedown pin hole in the lower square to each side?Don't file or grind on the upper or lower until all other options are exhausted or you are going to end up with a sloppy fit.