Man, I dunno for sure. It should be tight. Grab the lug/cap and really try and tighten it.
Maybe remove it first, reseat the barrel making sure the action is about half open/closed. Wiggle it and try and fully seat it, the put the cap back on and tighten down like your hand is a set of visegrips! Well, you know, as much as youre able to hand tighten.