There was an article in either Rifle or Handloader a number of years ago that did a write up on the M71/348 with load data. As I recall, RL 19 was one of the better performers and is where I ended up with my Browning 71/348. 200 grain jacketed bullets is all I've shot in it so far and I want to say around 65 gr RL 19, but don't have my notes handy.
