Way way back in the day when 7n6 was super cheap I invested in a S&W 5.45 AR upper from AIM.  It ran great and I never had any issues with it for years.  7n6 was banned from further importation and I moved and had to use an indoor range that banned 7n6 so it's been hanging on the wall of the gunroom for the better part of the last decade.   Not exactly sure how but sometime during that time period I lost the bolt and BCG.  Fast forward to now and I want to get it back in operation.  I ordered a stripped BCG and a 5.45 bolt from AR15Depot, but this new bolt won't chamber a round so my assumption is that it's out of spec/sync with the S&W upper chamber and won't headspace.  I thought the only difference in bolt was that the 5.45 bolts have a larger diameter for the slightly larger case head.....were there any other variations in 5.45 bolts for ARs and what would be a good source for a complete 5.45 BCG for this setup.  Also......I checked Brownells' for 5.45 GO and NOGO gauges but they are out of stock with no backorder....any one have a recommendation on a source?  Any help or insight is appreciated....thanks!

Your best source would be S&W.

Negative on that, I'm not getting any love out of S&W. They say I would have to send the firearm back in to them for repair/replacement but that I can't do that since it's an upper and the lower is not S&W.  They say my only other option is to go to a third party vendor and listed Midway, Numrich, Brownells', Jacks First Gun Parts, and lastly Guns and Gun Parts (in Springfield , MA).  I haven't checked with the last two but I have already with the first three and they don't have anything....I don't recall this S&W 5.45 upper being proprietary.

I have used several different 5.45 bolts throughout the years as well as various barrel sources but never the S&W stuff.
I've used the Red-X 5.45 bolts with no issues.
http://www.redxarms.com/category-s/1876.htm
Some info on my site.
http://www.c3junkie.com/?page_id=171