I wouldn't say its a lot harder based on barrel length alone, but I think on an SBR you are going to want to go with the M4-2000. The suppressor will be subjected to greater punishment on an SBR, and you are going to want the fully built model. The M4-2000 will be what I get when I get around to finally getting a suppressor, and I plan to change it between my 10.5" AR, and the XCR, which will probably be SBRed by that time as well.
Generally it is harder to suppress a piston gun than a direct gas AR, at least in terms of AKs vs ARs... suppressed AKs are in general much louder.
The one XCR I did shoot was fairly quiet though:
I assume based on that, that the XCR gas system is better sealed than an AK's.
Generally it is harder to suppress a piston gun than a direct gas AR, at least in terms of AKs vs ARs... suppressed AKs are in general much louder.
The one XCR I did shoot was fairly quiet though:

I assume based on that, that the XCR gas system is better sealed than an AK's.