On August 25, the night of the self defense shootings, Kyle was carrying a Smith & Wesson MP15 version of the AR15.
Dominick Black was carrying a similar version. I am not certain it was a Smith & Wesson MP15.
Both rifles were admitted as evidence in the trial, and both were identified by Dominick Black.
Since there was no crime associated with Dominick Black's gun, I would have assumed he could get it back, pronto, as soon as the case closed, since there is no need for it in the case against Black.