Give those 425's a chance. I think they will shoot well. I will be interested to see how the 300's shoot. Do you have the short barreled Marlin?? If you can not get those bullets to shoot then let me know. I am getting ready to cast some 405's without the GC, and I will send you a few to try. I never could get a GC bullet to shoot in my Marlin's. But I have only tried the GC's in two different guns. And I doubt if I can cast a bullet a well as the guy you are getting your's from. Are they sized at .458?? Tom.