In need of some info based on real, hands on experience
What is the scoop on the 450 Marlin chambered BLR's ability to function and shoot accurately (if I do my part of course) hard cast bullets?
Aware of the Marlins proven ability to do so, I like the versatility of the BLR to handle spitzer type bullets in 45 cal. (Swift, Woodleigh etc) for those shots outside of the FN cast bullets range (usually on the far side of 150-175 yds.)
Thanks for the input here.

Owning three BLR's I believe their barrels to have a smoother interior finish than late model Marlins. Since the factory .450 is a blunt round to begin with, I would imagine cast rounds to feed fine. Your central problem will be with the box magazine. You would be limited to ammo with an overall length equal to factory rounds which will leave you quite restricted as to usable bullet weights and designs.

I too have some cool Barnes .458" 400 grain spitzer SPs in the cabinet. I have found their net effect to be a gain of about three yards in effective field range. In practical terms, the .450/.45-70/.458 family are simply sub-200 yard performers, whether loaded to 1400 fps or 2400fps. Overall their bullet designs lack serious ballistic coefficients or section densities to have meaningful effect.

Choose the rifle that you like and enjoy. I like them both. If you pick a Marlin, the .45-70 case is a bit more versatile than the .450.

Long experience has shown that the best way to gain serious range with this group is to take one of those .458 cases, lube well, run it into the proper die, add suitable powder in the proper amount, then insert a 7mm bullet. Viola! Range problem solved.