If that is a Winchester Model 67, it is chambered for .22 Long Rifle, I think. No doubt, holding trigger to rear lets you remove the bolt. Looking down the bore, you will likely see that what rifling is left in there likely makes a turn or two - so a "spin" was imparted to the 22 bullet.
No doubt worth your while to find some instruction to remove the wood stock without breaking stuff. Since it was your Grandpa's gun, have to clean it up best as you can. Those old single shots almost could never be "killed" - but might need occasional luv with some oil - also some cleaning inside that barrel bore - even once every 50 years not a bad idea. You are not a millionaire for coming to have that - I would be surprised if somebody would pay $50 - but clean it as best as you can, and would likely function as single shot .22 for another however many years. Even just taking the entire bolt, as is, and drop it into a can of diesel fuel or kerosene - let soak for a couple days - likely as close to "good as new" as it will ever be.