I like tinkering with arrows and probably should've just scrolled past this post.
I've got a Ravin R10 that's collecting dust, which is fine with me and I've been enjoying shooting my recurves all year.
I'm going to check into building a heavy bolt for this machine.
3 Rivers Archery sells weight tubes for the inside of arrows and they come in 3, 5 and 8 grains per inch. Excluding the space taken up by the brass nock and tip inserts, I could stuff 18" of a 8 gpi weight tube inside the shaft. Switch to a 150 gr. broadhead, like a Tooth of the Arrow or similar one-piece construction. It's possible to build a 780 TAW bolt.
Of course, the 400 fps will be out the window, but the speed dial on the Ravin scope goes down as low as 300 fps. Even at 300 fps, a 780 grain bolt is going to hit like a freight train.