I use the 700mls and have done so for going on 6 years now, it hasn't caused me any concerns over that time. Accuracy is dependant on finding the right load combo, as suggested tinker with powder and bullet styles and grains. 3" is very acceptable for ML but you can better that if you find what she likes. My set up shoots 1" groups at 100 with 240 hornady xtp sabot and 100 gr pyrodex, when I do my part. I haven't been able to find a equally load for accuracy with 777 just yet but as with finding my original load it takes time and I just have been sticking with what works.

Also I use the cabelas 209 kit which apparently works much better than the remington factory for 777, so that might be something to consider.

T7- is right with the rems you need to put in some elbow grease and keep them clean. I completely disassemble my bolt assembly each time after hitting the range and have other little rituals when caring for my ML.

Best suggestion is to vary both your powder and bullets to try and find the sweet load...although do one thing at time!

good luck