Have a preban Colt Sporter Target that I bought slightly used---probably had a couple thousand rounds through it when I bought it. It was my first AR. Has a 20", chrome-lined bore and chamber with government profile barrel.
When I first purchased it, I installed a 3.5 Compact ACOG on it---mounted on carry handle. When I originally sighted it in (at 100 yards) it was pretty accurate just off the sand bag (no sling or anything special)----was able to consistently get 2-3" groups at 100 yards----whether using the scope or just the "issue" metal sights.
Since original purchase, I have probably put 4 5 or 6K rounds through it----mostly plinking----some 'blasting' where the barrel got pretty hot----using everything from lots of Wolf to SA Battlepacks to some Q3131A and XM193.
A couple of weeks ago I started to notice that the accuracy was way off---when shooting out at 200+ yards----I was a good foot off of target. Checking things out, I found the scope was loose----I tightened it up and then resighted it in yesterday.
Resighting in I found I had to significantly change the adjustments on the scope. Plus, using the metal sights, I had to crank the rear sight all the way to the left to get the bullets to "kind of" center at 100 yards---it used to be accurate as can be when the rear peep was just about centered between the rear sight "guards". Even with the adjustments, shooting SA, I was getting a dispersion around the bull of not 2-3" off of a sand bag, but more like a foot.
Not being an AR expert, is this just a case of barrel wear----or did the barrel somehow get bent---or are both those situations occurring?
I recall that there was one time that the rifle got knocked-over and fell a couple of feet-----when the barrel was damn hot----could it have gotten bent? I know that a SS brush got used on the bore once---but my initial thought is that that shouldn't "kill" a chrome lined bore, etc.
Any insights on this? I am looking at putting a Jewell trigger into it (I'd go with the RRA, but have the sear block to contend with)---I assume I should start looking at a barrel replacement, right?