I have two inlines, a T/C Black Diamond XR and a CVA Staghorn. The Black Diamond shoots a good group with the T/C Shockwaves all the way up to 120 grains of Pyrodex RS. I was shooting the Triple Se7en out of it and it seemed to shoot fine with 100 grains of T-7 which would be close to the charge of Pyrodex used. Anything above that and I got fliers.

When I shot the 295 aero tip power belts I tried 100 grains of Triple Se7en and was not impressed with the group at all. I think if I cut the charge back some, it would have gotten better but I ran out of projectiles to continue further testing and the next batch I want to try are the 348's.

In the manual of the CVA Staghorn 209 Magnum it states that the only 150 grain charge of power they consider safe is from three Pyrodex 50 grain Pellets. All loose Pyrodex must not exceed 100 grains. Triple Se7en therefore should not exceed 85 grains if the conversion tables are right. I shot the 295 grain powerbelts using 100 grains of TripleSe7en ( not even realizing I was shooting a "unsafe charge actually until it was pointed out to me by another poster.) and the groups were terrible. Yet this rifle with 90 grains of Pyrodex RS and a 240 grain T/C CheapShot will shoot a excellent group.

So even through the rifle is a magnum rifle, that does not mean you will get the best results with a magnum charge. All rifles are different your correct in that statement. As you said, all you can do is play with the load and see what works best.

By the way, how do the 405 grain powerbelts shoot? What kind of rifle are you shooting? And do you shoot pellets or loose? I am always intersted in learning someone elses tricks...