1/3 MOA past 1000 yards? That's kind of unbelievable. It's hard for me to imagine shooting bullets at targets past 1000 yards and each shot misses the point of aim no more than 1/6 MOA. That's what has to happen to hold 1/3 MOA past 1000 yards.I used Rich's load of 63gr Retumbo/140 Berger @3150 for 2011 hunting season-outstanding! For rocks and gongs-140 Nosler Custom Competition bullets with 60gr H1000 coasts along at 3050. Both will hold 1/3 Moa past 1000yds
The most accurate 1000 yard benchrest rifles will hold about 5/8 to 3/4 MOA at 1000. At least that's what they do in the many-shot aggregate records they've set. But then, once in a while, they shoot a 5-shot screamer that's under 2 inches. Then sometimes, the next group's in the 7 inch range. Maybe they're more accurate when not fired in LR BR matches.
On second thoughts, it's very close to unbelievable. Bless you, and your rifle and ammo, if it's so.