Ouch,
I'll go with Shamayim on this one. If it's a Colt barrel it's as close to Mil Spec as it can get, if it isn't a GI barrel anyway. As long as it has a quality commercial or GI bolt it's probably O.K.
If you really want it checked out, your unit "Armorer" can't help you out much. Now a days these guys are just Supply Pukes (92Y's)and other than account for the weapons and submit Work Orders if they are broke, are only concerned that you occasionally clean your weapon. If they aren't a 45B, Small Arms Repairman (Direct Support Level Maintenance) they don't have access to any of the Gages used to test for serviceability.
Sorry Tweak, but unit armorers don't even have Field gages. Actual Go and No Go Gages would only be found at Depot level, or the Manufacturers themselves.
If this still concerns you, A. Buy a headspace gage and do it yourself, it's easy. There really isn't any Black Magic involved. They're cheap enough and a good thing to have in your tool box anyway. B. Try to find out who the Direct Support Unit that does the Annual Gaging of your unit's weapons and make friends with one of the 45B's(Beer usually goes a long way), and have them give your rifle a thorough inspection. Your rifle sounds to me like someone assembled it on a Rock River Arms lower as opposed to a factory assembled gun, so it might be nice to know the condition/quality of the parts they used.
Wpns Man