I was bitten by the black rifle bug last week after looking at one too many overpriced WWII battle rifles. I took the plunge with no real knowledge, and probably overpaid for what was being sold as a Bushmaster  XM15-E2S with a Colt 20" 1/9 HBAR. It all looked to be in good shape, with upper and lower showing no  external wear. Got it home, took it to the range and found that it shot 4-5" to the left at 100yds. I had to adjust the windage quite a bit to get the shots close to center. What seemed to be missing was anything resembling a group. After a closer inspection at home with good light and good reading glasses, I can see that there is a gouge about 1/16" into the muzzle on one of the lands. And as the residue from the Sweets I was using to try and remove some fairly heavy copper fouling melted the black paint off the reduced diameter part of the barrel near the muzzle and  crown, I can see that there was something clamped onto that area at some point in time and that the face of the barrel has some pitting.  It looks like everything forward of the handguards was painted black, as the barrel is still green under the handguards. Another thing I noticed is the the barrel must have spun in a vice when it was being installed, judging by the galled areas. As if that is not enough, it looks like the FSB is canted to the right. I hope it is not the same problem another guy from WI had with a poorly pinned FSB. On the plus side, the lower looks like it is mint; even the BC group looks like it is nearly new. Now a few question: Is there a way to I.D. the upper? I don't see any markings that identify it as Bushmaster. I also notice that my A2 rear sight sort of cants to the left at the 8/3 position, then straightens out when raised to the max. I seem to have read that this is not a good thing. Is this a sight problem, or a problem with the the axis of the elevation screw relative to the carry handle? Or is it normal? Any advice will be greatly appreciated.

Glenn
Cudahy, WI

Oh boy,  The rear sight is normal, probably need to send the upper off to a gunsmith to recrown, repark and reassemble barrel to upper.

Uppers themselves are hard to tell apart.  save Colts (m4) and LMT, MEGA, There could be other named uppers

Glenn,

Does the barrel actually have Colt markings?  Can you post a picture of the upper and barrel?

Its possible that you picked up a parts gun that someone converted from a AWB compliant weapon, and that they did a shoddy job.  None of the quality finishes will come off with sweets.

Take it back to the guy you bought it from.

Hand it back to him Butt first , at about chin Height.

Seriously , How much $$ did you give for this "gem"?

If you got it fairly cheap - best thing is to just get a new barrel ( or maybe a used one off the EE here)

The rear sight is spring loaded , try setting it to Mechanical Zero.

ar15.com/content/guides/sightIn/

Quoted: Glenn, Does the barrel actually have Colt markings?  Can you post a picture of the upper and barrel? Its possible that you picked up a parts gun that someone converted from a AWB compliant weapon, and that they did a shoddy job.  None of the quality finishes will come off with sweets.

Stickman, the barrel is marked "C MP1/9 HBAR" which I was told was Colt. Once I saw the galling on the barrel I figured I was in trouble.
AKsRule, I paid $699 for it. I considered getting a new barrel and tools to swap it out, but right now I think it would be cheaper to just find a local 'smith to redo the crown and try to re-time the barrel.
Thanks for all the replies. I am headed to the range today to try to sight it in properly. If nothing else, I am learning the hard way on what to look for on AR's.

Glenn
Cudahy, WI