Depends on how big the gongs are... a 5+" grouping load in either jacketed or cast is going to be sketchy with an 8" gong, I think, unless you can reliably hold 2 MOA offhand shooting a Lee Enfield and its trigger.
Some specific cast bullets in milsurp sub-forums on cast bullet forums:
Military Surplus Rifles
Military Bench Rest Cast Bullet Shooting
Silhouette Shooting
CB Loads / Military Rifles
Military Rifles
You'll probably run into Wineman who advised you earlier on one or two of those forums, BTW, I would guess it's the same username.
His mention of the SAECO/Redding 315 tapered bullet has gotten me to thinking it would be fun to try that bullet powder coated. A heavy powder coat just might make that 30 caliber bullet into one that might work well in a .303 British.