.299/.308 Bore and groove

That is a standard barrel used for .308s by GA Precision (Bartlein 5R). I have several GAP .308s with those bore specs and they shoot phenomenally well; great velocity and outstanding precision. How they compare to a .300/.308 bore, I can't tell you that. Frank from Bartlein posted something here a while back regarding this exact issue; if you do a search you might be able to find that thread. Sorry, I don't remember the forum it was posted in.