J B Weld would be ok, but any good quality epoxy material would work. You can dye it, and also mix fine sanding dust from other gunstocks in the epoxy, to kind of reinforce it.
I just recently built a Pedersoli Penn Rifle flinter kit .50 cal, and did the whole barrel.
Just be sure to use a good release agent. I don't know what to recomend for that because I use exclusivly Brownells spray can release agent. It works on evry epoxy I have used. I get it at Track of the Wolff, as they have a good price on it.
If you are going to use Brownells Acra-Glass, I suggest the "Gell" type, as it has a longer working time, and is easier to mix (1to1) and, work with, because its not so runny. Its the kind in the green box. TOW sells it also.
Good luck, its not a hard job. It will make the rifle more consistant.
Dave