Need to remove a nice old horn buttplate, and it appears to have been glued on. Slight gap at the toe that I can fit a box cutter blade in, but that’s it. What would be best way to separate the stock and plate and end up with the plate intact?

Thank you.

Why does it need to come off?

Chunky rusty screws were extracted from it, and I would like that cleaning out any remaining rust would be good. I also want to refinish the wood. I suppose it can stay, but would be concerned about rust continuing.

It can stay on when doing your sanding and finishing. That is really the preferred way to do it.

If you plan on doing an acetone soak on the wood, that should
Not harm the plate, but will certainly loosen up the glue holding it on.

Heat may be something else to try for removing it. But enough heat will also caise the horn to bend. Just like a plastic buttplate will.

There is a method but it is painfully slow but does not involve large amounts of brute force. You will need to obtain a good quality guitar steel "E" string and a couple of heavy weights. Support the stock and action on a table with the but plate just protruding and in your case toe up. Next put the guitar string in the gap between the stock and the plate, then hang your heavy weights on each end of the string so they are applying a permanent downward force. Then heat the but plate with a hair dryer as hot as you can safely go, with the heat and weights on the wire guitar string, it will slowly cut through the glued joint. It is not fast but it will work given time.

That sounds neat. I’ve played bass for 40 years and mutilate guitars in my spare time. Plenty of E strings around the house.

Since you don't know what kind of glue was used,,could be anything from hide glue, to elmers, super glue to epoxy..go slow in your take a-part attempts.

Some of the glues respond well to some heat to soften them, others to heat in the form of hot water. Some like super glue will bind to the natural horn just like it does to your skin and separating the two means nothing short of leaving a (hopefully thin) layer of either one or the other materials bound together still attached to the other at separation.

Acetone will cut many fresh glues but older set up products are a dud. Epoxys the same in many cases.

You might want to just leave it where it is since it's a 'nice old horn buttplate' and should be in position when the wood is refinished anyway as already stated.

As far as the rusty, chunky old butt plate screws that came out of it,,that may be an indication of salt cured wood. Browning was not the first in history to figure that trick out and I've seen the problem on more than a few Euro shotguns of pre-WW2 age. French & Belgian lower grade and mid grades.

If the plate is OK and fits OK,,and the only situation you are trying to 'fix' is the old rust remnants down in the butt plate holes,,I'd simply leave the plate where it is. Then drill the old BP screw holes out as large as I could with it in place. Then plug the holes with walnut or other hardwood dowels glued in place.
Make new screws, which you will need anyway for the butt plate.

The new ones can be of a coarse machine thread instread of a wood screw type. They can be smaller in dia than the old ones, thread totally within the new plugs and yet they hold as well or better than the big wood screws often used. A #10 machine screw size is a good place to start.
They are easier to 'time' also.
Make the head and shank that extends down through the butt plate itself the same as the old screws so as to support the plate as original.

Refinish away.

Thank you. The only issue is the rust. The plate is nicely fit to the butt; nothing is proud or the other.

IME, that will no longer be the case if the BP is removed to refinish the wood.

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The plate was not removed in the end, and finished nicely with the stock.