Yep the levergun loads are best kept for the encore, you can shoot warm loads but a steady diet of heavy stuff will stretch the frame. The G2 will handle it longer than the old frame, as for the Leverevolution ammo I would consider it marginal as it's still a pretty hot load but a lighter bullet. With what the tech told you I might get a box of fresh stuff and see what happens but take a sharpie and draw a line around the top of the shoulder and fire a round and see how much if any it really is moving forward. On a shouldered round that is headspacing off the rim it's normal for there to be some change and if it were a centerfire that's how we would form brass to our individual chamber. If there is alot of change and it's still splitting brass then there may be a headspace issue. If the frame is stretched which I'm really not thinking hard along those lines at the moment there are corrective actions that can be taken by myself and couple other shops that use Bellms parts.