You may be in DEEP "poo-poo". Wood stock or plastic? From what I can gather, it can be stripped off with aircraft stripper or lacquer thinner. But you are going to ruin what's left of your factory finish if it's a wood stock, and it will MELT a plastic stock. You may want to entertain scuffing it up really well with 360 sandpaper and then painting a camo (or whatever) pattern over what's left.
scotch bright pad, wash clean, dry, tape barrel channel off, primer, dry, paint black. You can buy an automotive grade clear coat in low gloss and paint a few thin coats on to top it off.
Went for a carbon fiber look and it just didn't turn out quite like I was hoping for. Work done was OK, price was good, just didn't get the look I wanted.
Brake fluid and a toothbrush if it's synthetic and you should be good to go.
Depending on the paint/prep they did it may come off pretty tough. I recently acquired a Glock G30 with a botched OD green paint job....went the gun scrubber route only to find out it had a digital camo job under that....that digital camo was done right. I gave it a bath in brake cleaner...brake fluid...even aircraft stripper. To finally get all the paint out of the bottom of the grip stippling I needed to sandblast it with ultra fine media. It was a battle all the way, generally paint will wipe right off after brake fluid has been on it for an hour or so, I have no idea what that digital camo paint was but it was durable to say the least.
I own a Hydrographics company. If the job was done correctly you'll have to either use a ton of lacquer thinner to get rid of the entire job or you can use Aluminum Oxide (or other fine media) to blast off the finish. Duracoat as a base coat requires a little more effort if that's what he used.