Can you install any AR-15 upper on any AR-15 Lower? If not, then what Lowers will accept different mfg. uppers. or what lower is most "versatile". If I buy an AR-15, I would like the option to get another, or several uppers for it; what are my options?

basicly any upper will fit on any lower. the problem you might hear about is when you get colt parts involved. then special bushings and offset pins are needed for some of them to mate together.

There are two different front pivot (hinge) pins used ... a larger one (0.315") in some Colt lowers and those with the standard (military) diameter (0.250").

If you are looking for a lower upon which you can mount uppers from many vendors I would suggest you get one with a standard diameter front hinge pin ... that is, a non-Colt lower.

There is a pivot pin adapter bushing available that allows using large pin uppers on standard pin lowers.

Hi Mike,

Where oh where does one find that adapter?

Been looking for a large pin replacement lower, but that would be even better, that is, more economical. Asked where I could find a lower on the AR15.com site and no one mentioned a way around it.

Never mind...Midway and Brownells both offer them. Thanks!

Mr. Wilson,

Glad you found them. I would have directed you to Brownell's.

Have a great New Years!