Guys,

 I recently picked up a pre-ban Colt lower at a gun show and slapped my M4 upper onto it when I got home.  There is, IMO, a good amount of play between the upper and the lower but I don't know how much play is too much.  Can someone enlighten me?  
Also, what do you guys do to get rid of the play?  Several people have told me about Accuwedge, any thing else?

Thanks in advance - Marc

[url=jpar15.com/riflespc.htm]JP Enterprises[/url]
sells a "tensioner" rear pin. Bushmaster also sells these JP pins.

Is it a small pin lower or the large hole one where you have to use that offset pin / screw thing?

Also, is the lower a slab side or the one with the raised "fence" around the mag release?

SP1 / slab sided lowers can cause you some serious grief when using an offset pin to adapt a small pin upper to the large pin lower, because the pin can rotate in the hole causing the upper to cam away from the lower.  It can actually move enough to prevent you from closing the upper on the lower without rotating the pin back into proper alignment.  It can also allow the upper to be too far away from the lower to provide reliable function.

The later style large pin lowers with the raised fence will prevent the offset adapter from moving if you use the big headed pin / screw that colt provides, with the small flat milled on it that mates with the raised fence.

I have had lots of problems with slab sided SP1 type lowers and small pin uppers mating properly.  I would never consider using that setup in a self defense or LEO weapon.