Has anyone seen this before? It may very well not be cork but something was used to fill a cavity in the butt. Certainly looks original. Any model 21 experts out there?

Pics didn't load?

Without any further info, my guess would be someone has had a recoil reducer installed. A professional job would be barely noticeable under the buttplate and could look like a factory job, I suppose.

If this gun was used as a Skeet gun or if the owner was sensitive to recoil, it would not be unusual to see this.

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... Or if it were used as an upland game gun, lighter weight may have been the goal. I have seen stocks with a large (1"-1.5") plug drilled out (3"-5" deep) and a very short plug added as a cover for the hole, leaving a large empty spot within the stock, but a nearly undetectable repair under the buttplate.

Could be either one of these.

Edited to add: Unless your are talking about the checkered butt, where the surface of the butt end of the wood stock was actually checkered, with no buttplate. This was the standard on Model 21 Skeet grades, and a popular option on other grades as well.
That's all I have without seeing pictures.
Cheers

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