Instead of securing the rifle and then turning that long screwdriver handle, try putting the screwdriver in the vise, and turn the butt stock. You'll get more force that way if it's being cranky about coming out.
You can get a ring spanner onto the square end to loosen the bolt, this is a trick i have used a few times just to get it started, its also a good trick to get a good gap between the head of the stockbolt & the felt/leather washer to fish the washer out by undoing & then redoing the bolt up.
Just remember when using the spanner from that end its righty loosey, lefty tighty.
Things get a lot easier when the forend is off...impossible otherwise.
I've always used a wheel brace with the blade screw driver end, works great:
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I use a big screwdriver, and grab its shaft with a Vise Grip.




























