Customer sent me a Walther Automat, shotgun for restoration. The horn buttplate has shrunk away from the curve of the stock and the edges have rolled up so the surface that seats against the wood is convex side to side. Can I save the original plate by boiling in water to soften, then clamping it to the stock with rubber strapping? The plate is smooth with lateral grooves in the center and no trademarks or embossed designs.

I have boiled them to flatten them, and that will work but the biggest problem is usually the delamination and flaking of the horn layers; I have epoxy'd them back together with epoxy dyed the horn color; usually black. If they are shrunk smaller than the wood; nothing you can do about that. Horn was the plastic of the 1700s and they did a lot with it and it can be made quite malleable. It can also be ruined by heating or boiling; you can make jello out of it too if you aren't careful.

Mike, I have only worked with horn a couple of times. Perhaps those with more expertise will chime in. Being a natural organic material composed of protein and cells horn might not respond well to immersion and boiling. I might try a gentle method first. The horn probably dried out over a period of years, so I think I would construct a humidor or place it in a cigar humidor for several weeks to slowly restore moisture. Failing that, I would try it in a warmed sweatbox with 100% humidity for several hours, checking hourly.

i would think that it may be easier to make a new one

It is sometimes. As for boiling, I make a lot of powder horns; horn does indeed, respond well to boiling and heating with a heat gun. You can make it in most any shape you want. But you have to be careful. Can heat in oil too; that is the gentle method. Humid sweatbox wouldn't do much.

I will try heating in oil. I'll let you know the results.

I usually just use water; oil is quite messy.

Try putting a few drops of mineral oil in the water. It will absorb (not 100%) and help lubricate the horn naturally. Drug stres and grocery stores carry it.

Boil it in plain water. It'll get soft and pliable. Have the wood ready for it so you can put it in position and clamp in down. Use the original screws also as they will position it properly.

When it's hot and pliable it won't take much to push it back into the position you want it in.
Rubber bands work well but they can sometimes leave impression marks on the edges of the soft material.
Most can be sanded out in the final finishing but wide straps work best to avoid that.

It'll cool off rather quickly and hold it's shape at that point, so it's not like it has to sit over night with clamps or bands on it.

If it needs another boiling and fitting to get it right, don't be shy about running it through the process again to get it the way you want it.

Once fitted down to the wood like that and cooled off and dry, I drench the plate with super glue.
It soaks right into the some what porous horn material. But the main purpose is to get in between any delaminating layers and tiny cracks that are usually seen developing in the material.

It drys in a few minutes in the natural horn material and drys hard.
When finish sanded and polished, the plate is strong & solid w/no effects of the work showing.

Thanks for all the suggestions. Closer inspection finds it is delaminating and not worth the effort. Customer approved fabricating a replacement from new horn.