...As for rifling, there is no way you could get the foam to expand enough to grab any grooves while still having enough power to heave the barrel. The reason rifling works in real guns is because the heat expands the bullet and it grabs the grooves. If the barrel isnt detachable, it's nothing a hacksaw can't fix.
This is absolutely correct.
I took a closer look at the image and I believe I can see where the barrel detaches. It's just behind the tac rail that the bipod attaches to. See below: