It's been a while, so I forget things. Are the Federal 215 primers pretty new? I always thought a 300 win mag. got the federal 210 primers? What primers for a .243 win?
The Fed. 215 is the magnum large rifle. The 210 is the standard large rifle. Some loads in the 300 Win Mag work better with the 210, some with the 215. Start first with what the recipe calls for. With a couple exceptions, the 210 will work better in the .243 Win.
John
naa....fed 215's hav been around at least 40 yrs...they're listed in my speer #8 published in 1970...the federal 215 MATCH magnum primer is a fairly recent development....243win takes any Large Rifle primer...300win mag takes either LR primer or LRM (large rifle magnum) primer...LRM can be used in 243win but start at the minimum given load just to be safe...