I just re-read the original post and had assumed you were using 300 gun A-Frames, but it doesn't say that. I tried to 81.0 grns of IMR4350 with both 270 gun TSX and A-Frames. From your posted velocity, I think you used 270 gun bullets. I got about the same velocity as you did.
My Lyman's manual (49th ed.) shows a max load for IMR4350 with 270 gun A-Frames of 77.7 grns, but for 300 grn A-Frames the max load is shown as 81.0 grns. That's puzzling isn't it?
