Originally Posted by
O2HeN2
Sorry, that should have read "may be a problem" (fixed on edit). Though you might be able to resolve this issue at the Federal (read: ATF) level, I see no wiggle room in the Colorado Revised Statues if the firearm has been "defaced":
C.R.S. 18-12-103 (2011)
18-12-103. Possession of a defaced firearm
A person commits a class 1 misdemeanor if he knowingly and unlawfully possesses a firearm, the manufacturer's serial number of which, or other distinguishing number or identification mark, has been removed, defaced, altered, or destroyed, except by normal wear and tear.