If I were to buy one of those Colt SP1 uppers from CDNN (they have a teardrop forward assist and birdcage flashider) and mated it with a current produciton A2 lower (such as, say, a Rock River Arms), would the resulting rifle be historically accurate if I swithced out the grip with an A1 grip? Would an SP1 upper even fit onto a modern lower of a different manufacturer?

Should I stop being cheap and just shell out the extra $200-$300 for a complete SP1?

Thanks.

Neither the SP1 nor the current lower would be accurate for an A1 build. An SP1 upper will fit on certain Colt and Daniel Defense lowers only, unless you get a bushing or offset pin.

the  uppers that CDNN are selling, are not SP1 uppers, they are real colt A1 uppers, and will fit any standard lower with the small pin. I bought the A1 upper from CDNN with the bolt carrrier and charging handle, when they had those,  and it was a brand new upper in the plastic, and fit perfectly on my A2 lower...........as for historical accuracy, the A2 lower is a bit different from the A1 lowers, but not enough that will be that noticable, if you take a A2 lower, put athe shorter A1 buttstock on it and a a A1 pistol grip, it will look right.........the only thing is that the colors won't match, the CDNN A1 upper is gray, and the color of all the A2 lowers is black.