For years you have posted your favorite load in the Mashburn was the 150 BT on 70gr R25 for 3120fps.
My standard everday load in my Ackley is the 150 TTSX over 61.5gr of R22 which nets me 3100 fps on the nose with great brass life.
You mentioned BigStick, which is where i got the idea to build an Ackley. My light one is throated for 150 TTSX, the heavy for 162 Amax at length Larry gave me. That exact 150gr load above is one i got directly from Larry.
P.S. BigStick has said countless times in his posts (preadvent of the WSM) that the 280 A.I. was the best long action 7 going and if stuck wit a magnum bolt face to go no further then 7 RM. H has also repeatedly said that he has owned a 7mm/300 (basically a Mashburn) among most other big 7's and has repeatedly called them all useless goatphukks while reiterating the accolades of the 280 A.I and 7RM.
With the advent of the SAUM and WSM'S he got 280AI/7RM performance in a short action which is where he currently is and singing those praises. Except for his long love of the 223A.I. and now the 6BR.
I'm just guessing that what he meant about mag box constraint, throating and seating isnt what you got from it. I come to this conclusion because myself and several others on this and other boards have built 280AI's set up and throated per Sticks advice which you tried to use against it in your post above.
