I'm not going to model and make a print of it.. mostly because I don't want to rip my barrels out of the receivers, but I'll offer some insight.
There's an internal collar inside the receiver that the barrel shoulders on. Because of where that collar is, you have to have a shallow stepped cone on the breech face (easy enough to measure the take-off and copy it). If you try to flat breech it, you'll interfere with the bolt nose/extractor. The barrel OD in front of the receiver is the thread major diameter, and I believe it's 25x1.25 metric threads. There is no shoulder/engagement on the front of the receiver, the barrel just slips in and the threads stop before they show in front of the face of the receiver.