I wasn't able to measure the box my brother had for his M70 that he says is 4.1", it is at the gunshop. I wonder if he has the 3.91" confused with 4.1" because I don't see one on the sheet here for one "that" long.
The box it 3.91", like I thought, but this is outside dimentions, so you ca subtract a total of .100" for the likely .050" thick steel at each end. Now we are at 3.81", which happens to be about .130" longer than my 300 Ultra box. I wondered if 3.91" was the outside dimention, and it was. I would call Wyatts and see if this is the largest they have, my dad said they don't show one for the Rem 700 in the Brownells catalog he has, he just found that they did when my brother got his winchester box and it had these others on the paper inside, maybe they have even more too.
Here is a copy they send of what needs to be done to fit one in and the mags available at the time. Good luck.