Here’s a photo of the vent on No. 23, owned by a friend. You can clearly see the outline of the grain, aka bouch, under the paint. It is a wrought-copper, threaded vent bouch or grain. Another friend owns Parrott 10 pounder no. 26?; he reports it has a copper grain In the vent.I’ll post photos of the vent. I’ve seen other Parrott rifles, various calibers, and the top of the vent and area right around it are even and flat. The vent of no. 10 is hemispherical at the top. Theres a ”mound” of iron you can see. Why is that? Only thing I could think of was that it had been bouched with an iron vent-bouching aka “grain.” And not all of the square top end, which fits in the big tap wrench used to screw the grain in, had been removed. The present vent hole diameter is 0.275 in. A new vent is 0.200. John Morris has shared 2 photos with you!