Remington 100gn Corelokt (no crimp)
COL 2.730" (but seat your bullet depth according to your chamber/magazine dimensions)
43.5gn of H4831
CCI 200 primer
Fireformed brass
Hornady 100gn boattail (no crimp)
COL 2.695" (but seat your bullet depth according to your chamber/magazine dimensions)
43.5gn of H4831
CCI 200 primer
Fireformed brass
Both shot well at ~2800fps from an H&R single shot my sons used to have. Work up to this load as it is approaching 'warm'. You won't likely find this load in any of the books. I don't recall the twist rate of the American, but the 95-100gn bullets usually perform well out of just about any factory 243 barrel. Your mileage may vary.
-Steve