.505 Achilles? Cassill or Cannon? articles, load info.

by Cannon , Monday, September 03, 2012, 10:02 (4466 days ago) @ Rob Leahy

Not long after Jim et al. announced the 480 Achilles, Mark and I both had the same idea: Scale it up to the big Ruger frame.

480 Ruger brass was the obvious parent case, but it wasn't fat enough to make .510" bullets ideal, and was too fat to size the whole thing to .500".

We were discussing the possibilities with several other folks, and I think it was David Clements that reminded us that we could split the difference at .505" with a 505 Gibbs barrel.

Mark bought a barrel blank from PacNor, one of us sweet-talked Dan at Mountain Molds into modifying his online bullet design program to offer 50-caliber bullets with a .477" heel, and we both had molds cut. Our molds are nearly, but not quite identical, both looking very much like a scaled-up version of AaronB's 480 Achilles bullet. Weight is 360-365 grains.

Factory cylinders were rechambered using a .507" or .508" chucking reamer. Jeremy provided the Bridgeport mill and fixtures we used.

We settled on a .900" case length for no better reason than that's what Jim used on the 480. My load development pretty well started and ended with 7.5 grains of Unique. Velocity was 750-800 fps, and accuracy was surprisingly good. I had some longer cases I intended to use to work up a 1000 fps load, but after punching one of the slow loads all the way through a whitetail, never bothered.

I really need to find my notes from this project, as I made an attempt to keep track of everyone that helped us out. I know I'm leaving out some major contributors here.