Waited until I got home to my records to respond. Of course every rifle is a different story. Mine is a Whitworth that Jim Kobe modified for me, including shortening the barrel to 22".
I worked on load development with the 270 grain Barnes and RL15 last summer. The max load according to Barnes is 77 grains. On one of my trips to the range, I loaded 3 at 72 grains and shot them over the chronograph just to get a sense of velocity. That yielded 2574 at 10' from the muzzle.
The next time out, I took 7 loaded with 75 grains. Three shots over the chronograph gave 2641 fps which would be a muzzle velocity of about 2650 fps. I shot the remaining rounds at 100 yards. The first 3 went into 0.57" and the 4th opened the group to 1.28".
On the next trip, I took 10 rounds loaded with the max of 77 grains. Three over the chronograph gave 2702 fps, and the other 7 shots at 100 yards (with barrel cooling) gave a group of 1.53". It may have been my imagination, but I felt like there was a slight stickiness to bolt lift with these max book loads.
I decided to be happy with the 75 grain load. Don't think anything I would shoot would notice the slight velocity difference. And if both loads are zeroed at 200 yards, there is only 0.1" difference in drop at 300.
BTW, these groups were shot with a Leupold 3X with HD reticle.
