could do a SBR, but again, why? the whole point of 300 WM is velocity. chopping off barrel length just loses you velocity.
heres an article where they test velocity from 24in down to 16in
https://rifleshooter.com/2013/12/300...6-300-win-mag/
Personally, if you really wanted to suppress the 300, I would cut it down however long the suppressor is, or 16 in, whichever comes first to maintain the same overall length.