I load a 405 LBT LFNGC bullet in my 1895G and its OAL is 2.554" when seated to the crimp groove and it feeds fine. But, if I try a 450 gr. LBT LFNGC that is loaded up for my No. 1 at 2.640" it won't even come close to feeding. But this doesn't really answer your question, does it? If you are using Marshal's bullets your OAL should be just fine to feed through the Guide gun, but if using some other bullet with the crimp groove someplace else, the only answer I can give is you'll have to try it to find out, or have your Marlin's carrier/lifter modified to feed a slightly longer round, which is not a hard modification to do.