560gr., but what's 20gr.?

The suggestion by Elmer to use the 560gr. at 1,960, instead of the 500gr. jacketed RN at 2,059fps, was due to Elmer surmising that the cast would out-pen the jacketed bullet.

He did not trust Barnes copper tubing solids in lighter weights - or standard for that matter, preferring the steel jacketed ones covered with guilding metal, or a hard cast bullet as noted.

Yes - could have used the Barnes, however only the copper jacketed lead core bullets were available then - no such thing as a TSX or Copper Solid.