I use Acetone all the time and it will soften set glue, but it won’t completely get rid of the old glue “coating” on the wood. You have to use a bronze brush with the acetone, but really scraping the surface of the wood clean is best, even doing it with a scribe or sharp pointed instrument where it won’t show from the outside. I use ALL kinds of normally available and some uncommon epoxies and I don’t believe any are going to stick well to Gorilla Glue. I’ve only used Gorilla Glue a few times and was never satisfied with it because it left too many holes.
I cracked the wrist of my Navy Arms Brown Bess “Carbine” very similar to that rifle when I first started doing CW reenactments and did not yet have a percussion musket. I “hit the deck” in a war game and unconsciously reverted back to my training with M14’s in that you sort of throw the butt of the stock forward to break your fall. Yeah, it broke my fall, but not only broke the wrist as on your rifle, but it also busted two large pieces of wood out on the wrist. The Bess stayed like that for almost 20 years until I decided I wanted to fix it to sell/trade it in on a full length Bess.
After looking it over more than a dozen times, I decided I had to actually break the two pieces apart so I could clean the wood in the crack and so the Accra Glass would properly adhere. That was a heart wrenching moment. I also had to break off the two small pieces as they would not have glued back in place without scraping some inside wood so they would sit correctly back in place.
Of course, I was worried about the strength of even an Accra Glass glued wrist, so I got an 18” inch piece of 1/8” threaded brass rod and figured out how to cut two pieces that went into the forward part of the stock on either side of the tang screw and lengthwise into the length of the wrist where it would not show from outside the stock. .I started the holes for them using carbide cutters in my Handy Grinder, which is a Dremel Tool on Steroids, but a Dremel would work. After drilling the holes in the forward section, I used pieces of rod I pointed and that stuck out just enough from the upper part of the stock to show where the holes needed to be in the rear part. Of course, I had to adjust the holes and made darn sure the holes were large enough that threaded rod pieces aligned and would not cause alignment problems when gluing the stock back together. Also, I cut the holes a little cone shaped with the smaller end of the flat cone shape met up on each set of holes. With Accra Glass filling the holes, this made an internal dovetail joint where the holes aligned. Not sure if that was necessary, but it made me FEEL a lot more confident. I even acetone cleaned the threaded brass rod to the Accra Glass would be sure to stick.
I used Brownell’s brown dye on the Accra glass (Gel, not the plain stuff) and dyed it a bit darker than the rather blonde walnut stock. (Accra glass dries a lighter color shade than when you mix it.) I used Mold Release on the rear of the barrel, the lock, the trigger guard, the thumb piece and the tang screw. I OVER filled the holes and voids with Accralass and .as I was setting in the pieces and screwing things together, I took excess off with the pallet knife or Q Tips moistened in Acetone THOUGH I deliberately left the Accra Glass 1/16” or a little more high off any crack or void that showed outside the stock. I wrapped the stock with Brownell’s surgical tubing and even used the soft plastic jawed pistol gripped clamps in a couple of spots to ensure it would be held tight and in position. When the Accra Glass fully cure, I unwrapped everything and filed the high spots of Accra Glass until I got close to the wood surface and then used cabinet scrapers and other scrapers to get the Accra Glass even with the wood surface. .
I really needed to refinish that stock, but since it was a rather blonde walnut, I used a golden brown dye that hardly darkened the wood at all and yet the exposed Accra Glass was VERY difficult to see and I knew exactly where the glue lines were. I did not have to stain the stock much at all to cover the Accra glass.
I polished all the metal parts on that Bess and took it with me to the 18th Century Market Faire at Fort Frederick, MD not long after it was done. I brought along a bore light that fit down in the barrel and made a sort of “flag sign” I stuck in the barrel to advertise it for sale and slung it over my shoulder as I walked through the Sutler’s Area. Since the “price was right,” a LOT of people looked at it and even after I told them about the repair, most people could not pick it out. A Dealer actually wound up buying it and paid me my asking price without question. Actually, he had let me get about 50 yards down the row after looking it over carefully and then came jogging up to hand me the money.
As dark as the color is on your rifle stock, it would be much easier to match the color of the Accra Glass and after it cures, stain it a bit to match the rest of the stock. Yes, you will be able to closely see where it was done because you did it, but most people won’t notice it even on a careful inspection.
Gus