Originally Posted by CJStudent
Yes; you can switch out SBR uppers; you just can't put an SBR upper on a non-SBR lower. You have a hundred uppers for one lower, but you can only put them on that one lower.
The good thing for me with the Sig is that the Upper is the registered part - the reverse of the AR. Therefore, if I did do an SBR on my upper, I'd have to really do some converting to screw things up and become illegal...