Art, I took some measurements and yes, the metal cap is a friction fit, hence not waterproofed.
The length with the cap is 3 3/4 and only 3 1/4 without the cap.

Is it some kind of game call Angel?

Daryl, I don't think so. The way the metal cap fits, I think it was meant to hold something.

What is it?
 

Possibly a quick loader for a large (4 or 6) bore single barrel muzzle loading shotgun? The capped tube would hold the pre measured powder charge, the hole in the end would work for a neck lanyard. Wads and shot flask would be carried separately. I said a single barrel because I can't imagine anyone having just fired a 10 or 12 Dram right and left would want to quickly fire a third and fourth. :rotf:

What does that marking on the side of the cylinder say?

It says Made in Italy.

Those dimensions around the head and rim are very close to an 8 gauge industrial shotshell, which incidentally, fit my 1873 W&C Scott and my 1876 Webley.