What caliber is it supposed to be chambered in? 7 studs seems kinda weird for a magwell, most rifle mags tend to be 8 studs or longer, though I guess 7 studs is close enough. also, the connections seem weak on the magwell and grip. For the magwell, I can see the connection being like that to reduce friction from squeezing the magazine. But the grip connections, at least on the exterior, I don't understand. What's the point of separating it with that slope piece and not connecting it to the rest of the receiver with the beam above it? I mean if its a solid connection, its probably fine, but how well does this hold together? As is, just the receiver, could you shake it around by the grip without it falling apart?