I think that the 52 grain would still kick more tail than any other bullet for your application, unless you're in wind. HP shooters mostly use 69 grainers for 2 and 300 yards, but I use 77 grainers, as I can find myself in heavy wind at a match.
If you really intentd to shoot to 300 yards, try some Sierra 69 gr. HPBT and some Hornady 75 gr. A-max. Both *may* shoot in a 1:9 twist barrel. They're worth a try. Beginner HP guys who have 1:9 ratios have had some luck with these bullets. Basically, some barrel maker's 1:9 is quicker than others. If yours is closer to 1:8, then you might be in luck...if it's closer to 1:10, then you're going to be stuck with maybe a 60 gr tops. You can mark your cleaning rod and push it through and mark again where it twists one full turn, then measure between the two marks and you'll have an idea of where to start.
Is your AR an A2 model (with fixed carry handle)? If so, you could get started in Highpower competition, and shoot "reduced course" matches of 200 yards with it. When you decide to change barrels, you could consider getting a 1:7.7 or 1:8 and a free float tube, and shoot across the course! (2, 3, and 600 yards).
Oh, BTW, stay away from Winchester primers...many guys including myself have had piercing problems with them. Remington 7 1/2 and CCI BR4 primers work very well.