I have 6 700 BDL DM's, all with a few mags. I have had that problem with two of the mags. I originally thought it was the gun the first time it happened with a brand new gun, but I then put in an old mag it it worked fine. It is simply a mag problem.
Two things can be happening. One can be when the mag is empty and you squeeze the two release buttons, one of them will hang up a bit and maybe bind a little bit. The other is that when the mag is full and you push the buttons, one side will bind a bit or stick in. This is the problem side. (with 7mm's you have to load the mag so the belts on the ammo aren't stacked meaning they aren't all at the very back)
To fix the problem you have to do a bit of filing. It's a little tricky, but you can push down on one end of the shell plate (i think the back) and pull the opposite end up and out. Next there is a tab on the bottom rear of the mag that needs to be bent out to remove the release button. Next, I use a leatherman wave, you have to file all the mating parts so that the button can slide in and out smoothly. You also have to file the bottom of the shell plate. This fixes the shell plate coming down and interfering with the button. Once you are sure you did enough filing you can put it back together. Make sure you filed lots because you don't want to bend the tab more than you need to.
If you don't want to do the work buy a brand new mag in the package and try it loaded in the gun before you pay for it. The guy behind the counter will probably insist he does this for you!. Gun shows are full of used mags that need filing.
Happy shooting!
Gerich
