(Very nice, Dan!)
StevenV,
If you really need/want to go .225, then yes, it is certainly possible to stretch a piece of sheet that far. (But as Dan said, 1/8 is usually plenty.) If you do want to stretch a piece quite a bit, then you may want to start with a slightly thicker piece, so that you have enough to stretch w/o cracking the edges or getting thin spots. You can then file back the pipe and the finial to a thinner dimension. (Or hammer them to shape, which also thins them down.)
A few old rifles had a highly pronounced "bump" between the pipe and finial. (Even more than what is shown in Dave B’s photos above.) On such pipes, the step up in the wood is generally within “typical” range, but the bump itself is sticks up higher. For an example, see the rear pipe on the famous RCA 42 (same rifle shown in William Ivey's book, #101"). Hershel House has used a similarly high “bump” on many of his Woodbury style rifles, including this one:
http://contemporarymakers.blogspot.com/2008/12/hershel-house-double-patchbox-rifle.html Such a detail doesn’t seem to have been a common feature on antique rifles, but it does occur, and perhaps more often on southern rifles than those from PA. (W.Gussler attributes RCA 42 to North Carolina Moravians.) A well sculpted bump or other raised relief feature there can lend interest to the transition between the forearm and rod groove, and artistically improve an area that can otherwise be aesthetically weak.
The reason I mention all this here is that some contemporary pieces seem to have intended to use such a bump, but the builders haven’t stretched it correctly. The result is that the pipe finial as a whole ends up being too high, which then requires too much of a step up in the wood at the transition from the rod groove to the forearm. The bump, if appropriately made, can give that transition point an illusion of “boldness” and strength without requiring an overly heavy forearm. The thickness below the rod hole is generally the same whether or not the rear pipe has such a bump. That is to say that a pipe with the bumped up area does not require a deeper forearm.