Gary,
That protrusion is the wedge that was used to regulate the barrels.They are usually cut off and finished flush,but I had one left long in case I have to have it re-regulated. Your rifle was likely regulated with European ammo and you may have to try different loads.This is where handloading comes in handy.I would start with 180 gr bullets.If they shoot wide,they need a little less speed;if they cross, they need a little more speed.
Mike