Nice price, especially for a 20.
Look for the common things,, matched #'s, loose breech, cut bbls, ect.
Yes, they are a thru-bolt stock. They should bed tightly onto the receiver and the front face of the wood. If they get loose there, simply tightening the thru-bolt pulls the action back further. A little can be OK and make it well again.
If there's too much room to take up, the tightening will just pull the large diameter rear tang post into the stock like a wedge and crack the wood.
Over all a pretty simple & stout action with little to go wrong.
The cocking rods sometimes get worn and lift the hammers a bit late,,so the firing pin(s) may drag a bit. Sometimes just switching ammo will cure the problem well enough for you that a major repair can be avoided.
With the gun UNLOADED,,dry fire one bbl and then unlatch the top lever with the gun in the horizontal position. Let the bbls drop of their own weight slowly till you feel them start to pick up the cocking rod/hammer engagement. Take a look at that point how far the (top of the) breech is open.
It shouldn't be more than a few .000" at that. That's how far the bbl will have to move with the firing pin down hard onto the fired primer with the bbl rotating the case upwards as it is opening. Case dragging...
Do it with the other bbl too.
Harder primers in different brand(s) of ammo help disguise the problem as the firing pin doesn't bury itself into the primer as deep when fired.
The only real way to see if everything's in order is to shoot it of course,,but that's not often possible.
