I'm trying to put my colt sporter 2   back to orginal form . It currently is equiped with a flattop -a3 type upper receiver and has the wrong bolt carrier . I think that it should a large hole 603 type  upper . What !'m hazy on is I'm seeing the 715 /c7 type upper on some of the forsale guns .One has a sn of 341xxx with a 715-mine has sn of 331xxx. Any one know the breaking point  for these two receivers and the correct style of bolt carrier ?

I've seen Sporter II's with both A1 and A2 uppers, but have no idea when or IF there was a point where they changed. Colt tended to use whatever they had on the shelf - witness all the M16A2 lowers out there that are really A1's. IIRC, the BC was a modified Sp1 - so a half moon at the rear, or 'open' so a lightning link could not be used. They also put blocks in the lowers on the rear shelf, which I'm sure you know. I've never seen a large hole, C7 upper, but it wouldn't surprise me any. Not sure if this helps or not.

ETA: Check out the SP1 database near top of the page - that may help you out.

Thanks for the info.  I failed to mention that my lower is a sporter 2 A2-i'm thinking model 6500 . I was hoping that the bc would sp1 type  not the open c type !

Correct BC is SP1 type on every factory Sporter II I've ever seen.  Half moon didn't come around until post-89 when they stopped calling them "AR-15" and started putting in the physical sear-blocks.

My ca. 1986 factory Sporter II (306xxx) is slick and slab, with an SP1 BC and field sights.  Its A2 features are A2 buttstock, A2 pistol grip, and A2 barrel/fsb/handguards (round A2 hg, 4-pos square sight post in FSB, 20" C MP 5.56 NATO 1/7" A2 profile barrel with A2 half birdcage FS and peel washer)