Dinny,
I've shot 250gr spitzers in my 1:16" RMEF Whelen with no problems at 100yds, dunno what they'd do at 200-300yds tho. I don't recollect anyone saying they had a 1:18¾" twist 357Mag barrel on the poll that we did once upon a time, not saying they don't exist, just that the source at H&R for the twist info may have been old H&R Inc info.
Tim