Frozen screw...

[M1 Thompson]

If the forend is indeed scrap why not just remove the whole of the volley sight plate & screw assembly from the wood? You can get at the metalwork then. The volley plate screw is cheese headed, incidentally. The threads are likely rusted into the volley plate though there may well also be some adherence of the corroded shank of the screw in the wood.

Even if the forend is damaged further by the removal of the metal, it still has uses. I use such scrap pieces of woodwork as 'donors' for patches needed on otherwise serviceable woodwork. For example, the raised & rather thin piece of wood that often breaks off, located at the right rear of the forend between the charger guide recess & the very back end, can be carefully salvaged & grafted onto a needy piece of wood (glued & dowelled/brass wired)........pieces can be cut out of the area of the trigger guard recess & grafted on to another piece so as to make it usable again......& so on. Waste not want not!

That's exactly my plan, Roger.

[M1 Thompson]

I just thought of this. I snapped off two bolt heads changing a thermostat on a car. I heated the stubs to red, sprayed them with WD-40, and aftercooling backed the bolts out with no problem. I thought I'd do something similar with this.

A point to bring up, what was the original finish on the plate, in case I have to refinish it?

[Roger Payne]

Rust blued, but smaller component parts when they were refurbished were often oil blacked.

[Scout Sniper]

You shouldnt need to heat this to red, you risk causing too much damage to other components.

Have you actually tried any of the suggestions?

[Bruce_in_Oz]

I recall the "blacking" technique was called "blazing off" and involved heating the component (but NOT to a sparkling red heat), briefly dunking it in "oil" (probably whale oil in the "good-old days") and then letting the remaining heat IGNITE the oil on the component. This was done to small components that could not sensibly be "slow-rust" "Blued / Browned", etc. (Imagine the fun to be had rusting and manually carding-off all those tiny pins, screws and "knickknacks" in a SMLE It was NOT applied to larger components nor, especially those that had been heat-treated to a specific hardness. Bolt bodies were partially "blacked". I've seen the "finish requirements and specs thereof "somewhere".

Also, Lithgow was playing around with "Parkerizing" before WW2 as it was seen as a more consistent finish for several components, including the body and the magazine. It appears that they were using a "Zinc' based brew as there were concern of the finish "not being black enough" for service acceptance. Manganese-based Parkerizing is distinctly darker in colour.

Once more, into the dungeon!

There is a VERY good reason most modern commercial gun-makers use HOT blue systems like DuLite, for example. It might not look as spectacular as a bespoke slow-rust job, but you don't have to have unlimited funds to buy the finishd product, either.

[Roger Payne]

I had a few moments spare whilst working in the garage earlier & decided to see how long it would take to get the heavily corroded screw out of the volley sight range plate. The whole procedure took less than ten minutes, much of which was waiting for the assembly to cool enough to handle with my fingers after I'd heated it.

Firstly; clean off any loose rust with a wire brush before heating the screw - you can use rather more than you could if it was still in the woodwork, but not enough that it would affect heat treatment on a nice example (the screw is obviously scrap on this one anyway).
Secondly; douse in cold water to fracture the rust bonds between the screw & range plate threads.
Thirdly; gently warm to evaporate water, & then dip in penetrant (brake fluid in my case).
Ideally I'd leave it in penetrant for 24 hours or so, but I only had a few minutes, so that's all it got!
Fourthly: hold screw firmly in vice (vise in North America), & wind off the range plate using hand power, or a small set of grips if necessary (with the grip jaws padded to avoid damage to the range plate edges).

Give it a try. I'd be very surprised if it doesn't work. If the screw does get damaged then pm me as I can probably find you a replacement.

ATB.