Pinecone,
Thanks for the pointers. The gun is rust free (at least on the outside) as it has been taken hunting only once and was maintained (wiped off and oiled) frequently. I doubt it's problem is internal rust, but I will pull the stock off and take a look anyway per your suggestion.
My Dad bought this one new back in '66 or '67 and had it by his bed until he died in 2001, never firing it himself. (the gun has no serial number)
I put less than 500 rounds through it since then but I've cleaned and oiled it after every outing. It has always been stiff to open, either cocked or not. It is a little stiffer upon cocking, then if you close it and then reopen it without pulling the triggers, it seems to have two stages of stiffness.
The first stage of relative stiffness, is upon initial opening the action, then, it has a sort of second stage upon the last 1/2" or so of opening to it's wide open position. It is this last stage of position that is the most tiresome; it wants to close back that 1/2" of opening back to the initial stage...then you have to muscle it back open that last 1/2" again to make it stay wide open. If you don't consciensously hold it open, it will want to close up enough to hinder loading it. Then you have to muscle it wide open in order to load it.
In looking under the barrel chambers area onto the receiver when the gun is open, I can see the cocking plunger bearing against the sear(s)? and this seems like it might be where the stiffness is coming from; but I'm not sure.
When I take the barrel assembly off, there is no rust apparant anywhere either underneath the barrels or in the frame area where the firing pin holes are or on the frame that protrudes underneath the barrels.
It just looks brand new everywhere except for a few scratches on the stock and forearm.
So, I don't think rust is the problem.
I've not seen a firearm yet I can't take apart and put back together, so I don't think this one will be a problem either.
Assuming rust is not the problem, is there anything I can look for specifically when I get it apart?