Why? The 300s recoils on metal slide. Bedding the stock just may affect the slide system. Never heard of anybody bedding one. Maybe Joe will chime in on this.
There is older guy that shoots 10M benchrest locally that did his and he said it made it more consistent. Can't really argue with his results, he shot 498 out of 500 this week getting beat ny a Anschutz PCP that shot 499.