I'm not seeing this as a double standard, as he is using it as a tool and shit happens on the job.
What would happen though of a civvy looses control of his/her SBR? Kinda interested to know since I have one.
Depending how you have ownership of the SBR registered it could very well be a federal offense. If you personally own the SBR then you are expected to know where that weapon is at and can't just give it to your buddy to take to the range. If buddy wants to shoot it you have to be physically present during the range session. If you have the ownership of the SBR inside a NFA gun trust and you add your buddy as a member of the trust he can take the weapon to the range solo.
There are definitely unique handing considerations when possessing/storing/transferring/transporting NFA items. With all that being said I still have no idea what double standard we are looking for.