Dancing Bear, When I first started shooting my Whelen I was able to use somewhat higher charges of RL 15 compared the newer stuff. I believe Alliant changed the powder a few years back to be temperature stable so something must have changed when they did. Nosler lists 59 gr of RL 15 for a speed in the high 2700 fps range (I can't remember the exact speed off hand, 2789 fps?) so I can't see why you would need to reduce your loads when you are only getting 2600-2640 like you state. When you buy a new lot of powder I would difinitely start low and work up carefully. With the newer RL 15 I get around 2650 fps with 57 gr and 225 gr bullets in my custom gun.
