You have a WE MSK handguard on one of them? I can barely tell the two apart....actually, I don't know which is which, haha!
OK, this is a dumb question, the lower receiver is generally the "firearm" according to our laws......but the serial number is stamped in the uppers on our ACRs......?
Clarification: this pic does not have the MSK on it
I need to get a new picture done!