111 DBM Loose Magazine Causes?

The rear of the drop box magazine on my 111 International Trophy Hunter is quite loose and it's driving me crazy. The rear part of the magazine has a little tang (on the metal body of mag) but I don't really see anything inside the stock for it sit on. The front clips in nice and tight and flush, but the rear is sagging. Any ideas? I Just bought this rifle very lightly used. I'm very happy with it, minus the DBM issue. It's a 7mm Rem Mag with synthetic stock if that helps.

I'd appreciate any help

It does have a matching little lip that should engage it when you push it up. For lack of a better way to describe it, it looks like a small arm/ramp maybe 1/8" wide rear/center of the DBM frame and towards the top of the DBM frame.

Thanks Speedrat1. I see what you're describing, but for some reason the magazine has to sit a bit higher than this lip to have the bottom of the magazine flush with the bottom of the stock. So, what's happening is the tang on the magazine isn't resting on the lip inside the stock until the magazine sags a little below a flush position (if that makes sense). I'm thinking about a Boyd's stock. The new stock should be setup to accept the DBM and let it clip in flush, no?