What I would do:
Green scotchbrite the stock.
cut yourself up a white cotton shirt.
Apply True Oil with shirt. When I say apply, I mean heavy wet coats. don't be shy with the stuff. If the action is bedded, clean the bedding with alky and use a good automotive grade masking tape everywhere you don't want finish to build up.
Scuff again with green scotchbrite.
Apply more true oil.
Repeat this a few more times. You just want to "etch" the surface so that the next coat will stick. You don't sand it down. Your building up layers to seal up the wood. Since it already has a finish it'll be mostly sealed already which is good cause the wood won't swell up on you saving a pile of work.
Be careful around any checkering. Loading the finish there will just make it look like crap and it's tough to go back and dress the lines up if your not experienced with it.
Then start sanding with 320 working up to 1200. Apply additional coats between sanding sessions and allow to dry. Wet sanding works and when you get to the 1200 grit wet sand with the True Oil. let it sit for a solid week after sanding and then go after it like you would if you were spit shining boots. Just a soft cloth dipped in True oil.
When you are all done carefully remove the tape and then get yourself a stiff piece of plastic (a bondo applicator works good) and use it to scrape the excess along the bedding/showline surfaces and anywhere else it built up. Bolt handle inlets can gunk up on you too as well as around floor metal mortises. If your inlets are nice and tight take care while doing this so that you don't go too far.
Results can vary but this is what it looks like when I do it: