Does/has anyone shot hardcast thru their micro-groove barrels? I was thinking of shooting some 210 RNFP(no gas check) thru a .44 Mag. Will leading be an issue? What kind of velocities and loads? Thanks for your input.

Slug your bore and size +.002 and you wont lead up to 2 k.
Have used nothing but cast in my Marlins 336, 375, 1895

+ 1 to what deerstalker said. Marlin bores run big and if the bullet is undersized you will get leading with either standard or microgrove rifling. I run .460 bullets in my 1895 from mild to 1850 fps with no leading issues without gas checks as my sizing die knocked them back to .458 and caused leading problems. The 1886 copy did great at .458.

No problems so far with my 444 Marlin and 300gr cast with gas checks.

Sweet Jorge! What velocity?

The only issues I've had with Marlins is the leade, which I've reamed on several.