My experience with Montana rifles is limited to two, one of mine and one of my shooting partner's. Both have/had some serious issues. Mine was so badly over headspace that I ended up re-barrelling it, and my friend's is also showing the dreaded garbage can lid sized primers. There's something wild going with his, even necksized cases that fix the head space issue have to be loaded down to 2650 fps (300WSM) before pressure signs are sort of acceptable. They can't all be bad, but jeez.........to hear the gun rags talk about them they must be the best thing around. I hope they got paid well for their stories.
I've got a M70 Alaskan in 375, I really like that rifle and have several FN manufactured M70s. Did have one 30/06 that shot 3 inch groups that I returned.