I got to 4010fps with 66gn Bergers in my .243Ackley, before primers started to flatten. Ended up at 3980fps with superb accuracy. Perfect foxing tool!Have broke the mithical 4000fps with 55gn 243 and 95gn 260, both lightest for caliber bullets, with pressure running has high as I'd dare push it, not keen on sticky bolt lifts and popped primers!!!