I'm thinking if you're zeroed at 200 the holdover at 300 is only a few inches so if you know the target diameter, it should be fairly straightforward.
If you zero at 250 you may not have to adjust your hold. My .308 is a little slow, but my .270 and .30-06 both have right at 6" verticle change between 200 & 300 yard when zeroed at 250 yards.
