pretty sure it is .408 and that was what was told to me. My question though isn't the RL-15 more like the Kynoch .408 round 400 grain bullet around 2100 fps? the load I have in hand for this gun is 78gr 4831 woodleigh .408 400 grain and federal 215 crimped to the cannalur on Rigby Brass?

The other is 68 grain RL-15 1 gram poly

yes i do have Grame Wrights book and it is alot information.

Oh and were in the heck can you find federal 215 primers. I have some CCI250 will they work?