As an avid firearm person I'm always on the lookout for a good deal.  I came across a feller that wanted to sell his AR upper because it just didn't shoot well any more.  I bought it and found it to be a colt Large hole front pivot pin. I proceeded to thoroughly clean it and found that there was so much carbon built at that gap at the end of the riflings; it caused the bullets to loose accuracy.  I cleaned that up and now have a great shooting pre-ban upper. In hopes of scoring another great deal I contacted the fellow for the lower and no he didn't have it anymore.  Oh well, when I win the lottery maybe then I will be able to afford a matching Colt lower.
More details: A1 type upper, chrome lined, milled M16 sear relief, bird cage flash hider, hand grips are round ribbed style. barrel length: i'm not sure how that is measured, it is 16in from handle to distal end of flash hider.

[beer]

Sounds like an SBR upper. You need to measure the barrel length, to make sure you're legal without the tax stamp, before you mount the upper. You measure the barrel by putting a rod down the barrel to a closed bolt, and "non-permanent" flash hiders do not count toward length.

Swap out that ridiculous large hole upper receiver for a real one and you can use it on any lower you want.  Might as well get an A2 or flattop while you are at it, no need to search around for another A-1 upper.  A nice upgrade.  Swap out the front sight post for the square A2 type.

You assumed this large hole upper was my only upper.. Shame on you