The few times one needs an impact driver makes it worth the money.
Lacking the impact driver,,,,,
Assuming you are going to remove the stock to service or repair the firearm, you might take the action and put it in the freezer. This will cause parts to contract, maybe enough to remove screw. Inserting the driver into the screw, tapping it with a hammer while turning the driver has worked many times for me.
Putting a little candle wax on the screw when re installing it will help the next time.
If working on a rear tang screw that goes into wood, it may be rusted.
Obviously, if you leave it in the fridge overnight, when it warms up, it is going to sweat. The stock is going to have to come off.
If you are going to service the arm, if it is a newer model, make sure you have the firing pin tool to remove and retighten the firing pin retainers.
If the gun has been in service for several years, get mainsprings as well. It may need hammer cocking foot springs as well.
These guns can require numerous small parts. It might be a good idea to call Don at SKB at 800-752-2767.
The SKB/Weatherby is a good design, with VERY quick lock time, and is actually superior to many more expensive shotguns. Like the Perazzi, it likes attention, but is more difficult to work on.