Been using 4064 which does ok at 100 yds. Some say I might do better at longer ranges with a slower powder. I'm thinking they might be right because of the 29" barrel. Is Hunter capable of good accuracy out to 300 yds with loads no higher than 45,000 lbs pressure.or is it more effective accuracy wise at higher pressures?
The Ramshot Rifle powders all seem to preform best at full pressure, and your 45K PSI is not within that range. Doesn't mean it won't work but you will have to see by trying.
The persons giving you advice about slower powders for long range accuracy are either misinformed or you misunderstood. Accuracy means consistency and you can certainly find consistency with with medium burning rate powders like 4064.
Slower powders will help you find velocity in your long barrel but not under the 45K PSI range.