That may be one of the compression fit plugs that used an o-ring to make the seal. The Huntsman was changed to a threaded plug after afew deaths were attributed to that type of plug.I've not owned one so a picture of the plug would help. If it is the compression fit type plug, you may be able to push it out with a good range rod. In any case, make sure that bore is EMPTY.

The folks at Kittery Trading Post have sold a lot of those rifles in the past and probably know the ins and outs of the design. 1-800-USA-GUNS (872-4867)