certain Brocock rifles only take the new style Flip open magazines. You can tell by looking at the pellet feeding probe. if it has a lug on the top about 1/2 or so from the tip, it takes the old-style magazines. That lug engages the spring-loaded detent that allows the magazine to rotate.
the newer style with the flip open cover does not have that detent and so the pellet probe does not have the lug.
I bit the bullet for my Concept XR and purchased two new (Old style) Factory magazines from Mundilar in Portugal.
With three magazines, I'm good for a while, but may purchase a few aftermarket ones just for the heck of it.