I have used the Barnes TSX 85gr. and the TTSX 80 gr. a lot in my Mauser 6 mm Remington. For S'nGs ([bleep] 'n Giggles) I downloaded some loads to emulate downrage performance at super longrange w/o shooting so far.
I later used 2300 fps as my lowest impact velocity - and that is well high, I am sure.
If you load for 2900 fps (also conservative, me thinks) you would still be up that 2300 fps threshold and well within the performance envelope of the 80 gr. TTSX in your sons .243.
