If I'm not mistaken, the BIG MAC stock has a versapod spigot? I recommend checking out your nearby European cohorts at Roedale Precision. I had their RH50 MKI bipod and thought it was great.
I have the APA bipod on a mcree stock and it is way strong for that round. Mine is a 375 cheytac and only fix I came up with was I changed the angle of the legs to be 90 degrees instead of 130 or so.I have had them all too Cheytac and Windrunner attached this rig.You could not break this thing
Check out the bipods from LR accuracy. It is a very stable and rigid bipod. Legs can adjust for different angles and it can cant 30 degrees either direction and lock down. Mine is a pre-production version so it is not anodized and has 2 different leg extention methods. It attaches with a picatinni rail on the bottom of the stock so it should work with your big mac stock. You can use differnet feet with this as well. This is designed to rotate around the barrel axis which puts more weight down low for more stability.
I am also trying a 200 series bipod from RND edge in the next couple weeks but I think (?) you would have to go with a side mount to make his work for your big mac stock.