Obliterated serial number is a 5-year felony.
Possession of a stolen firearm is a 10-year felony.
The fact that they would be in connection to a separate felony only makes things worse.
18 USC 922(k): It shall be unlawful for any person knowingly to transport, ship, or receive, in interstate or foreign commerce, any firearm which has had the importer’s or manufacturer’s serial number removed, obliterated, or altered or to possess or receive any firearm which has had the importer’s or manufacturer’s serial number removed, obliterated, or altered and has, at any time, been shipped or transported in interstate or foreign commerce.
18 USC 934(a)(1)(B): whoever—knowingly violates subsection (a)(4), (f), (k), (r), (v), or (w) of section 922...shall be fined under this title, imprisoned not more than five years, or both.
I can't help you with the stolen property issue.
I am unaware, but would not be surprised to learn of longer sentences imposed for the underlying crime under the Federal Sentencing Guidelines for either situation.
Cheers, Otto
ETA: Found it.
18 USC 922(j) It shall be unlawful for any person to receive, possess, conceal, store, barter, sell, or dispose of any stolen firearm or stolen ammunition, or pledge or accept as security for a loan any stolen firearm or stolen ammunition, which is moving as, which is a part of, which constitutes, or which has been shipped or transported in, interstate or foreign commerce, either before or after it was stolen, knowing or having reasonable cause to believe that the firearm or ammunition was stolen.
18 USC 934(a)(2) Whoever knowingly violates subsection (a)(6), (d), (g), (h), (i), (j), or (o) of section 922 shall be fined as provided in this title, imprisoned not more than 10 years, or both.