How to cut a “Jug Choke” - Thanks to CoyoteJoe for this info, revised from a 2009 post:
Lot's of people ask how to “jug choke” a barrel.
I won't try to do a how-to "tutorial" here because most of the actual work is done entirely by "feel". With experience you know how the tool is cutting and you learn to recognize the right feeling when it is working smoothly and what to do when it is not right. A brake cylinder hone or similar tool, used with Brownell’s DoDrill is guided by the bore itself and thus is always straight and centered to the bore. Don't even attempt this on a chromed bore!
I use a home-made wooden tool holder similar to one used in black powder era "scrape cutter" rifling machines, except that it is rotated, rather than drawn lengthwise through the bore. This permits a longer cut about 4 inches long. This gives much better results than a typical automotive brake cylinder hone which is only about 1-1/2 to 2 inches long.
The tool must be able to enter the bore without cutting, have its' cutter elevated to firm contact while cutting, then retracted to leave the bore without further cutting. A thin, "L" shaped piece of flat stock, I call "the adjuster", is tapered in thickness for most of its' length. It sits under the cutter, between the cutter and the backing. When removed the cutter retracts to enter into or be removed from the bore. Once the tool in in place and cutting is to begin, I insert the L shape adjuster to raise the cutter until you feel firm resistance, then by rotating the tool it will begin to cut. After just a few rotations the cutter will be loaded up with cuttings and to remove and clean it I just slip out the adjuster. After cleaning the chips off the tool and oiling the bore, the tool is slipped back into place, the adjuster reinserted to the point of firm resistance, the tool is cranked another dozen or so turns, then again removed and cleaned. As the recess deepens the adjuster moves farther inward to keep the cutter cutting.
Oil hardening tool steel is purchased in soft condition to be easily cut with a hacksaw and filed to shape. The cutter is then heated to a uniform bright red and quickly quenched to be glass hard. Then it is stoned to a very smooth and sharp cutting edge with just a bit of draft to put the pressure on the leading edge. A common problem is was that the cutter may tend to warp when heated and quenched. While you can use a torch, a small forge will heat the full length of the blade without warping. The cutter must be very sharp, very hard so as to remain sharp and must fit into the backer very tightly and set on the center line of the bore. When your tool is working properly the cuttings from the roughing cuts will resemble wood shavings produced with a sharp scraper.
It is important that the cutter fit very tightly into the slot in the backing, because any "wiggle room" will cause chattering. Keep the cutting edge sharp, use lots of cutting oil, take it slowly, removing and cleaning the cutter frequently, go real easy using a light touch on the finish cuts and it's a snap.
While turning the cutter apply slight pressure to keep the tool against the stop. On finishing cuts you can let it wonder a wee bit, maybe 1/8 to 3/16 inch in and out, which seems to create a smoother recess without deep scratches. Finish cuts take longer than the roughing cuts but remove very little material, maybe a couple of thousandths, just enough to get to the bottom of any deep scratches. If the tool is kept sharp, well oiled and frequently cleaned of chips there just won't be any really deep scratches. Some people use a Brownells barrel hone for final finishing, but a sharp, well oiled and lightly handled cutter leaves a surface smoother than the Brownell’s hone. It's all in the touch.
The old standard for 12 gauge full choke in black powder days was .040" constriction. Modern guns and loads don't need that much constriction, but with muzzleloaders we are duplicating the old loadings. In modern cartridge guns using modern loads with plastic shot cups I consider improved cylinder to be the most useful all-round choke. Just enough choke effect to make patterns round and uniform with dense center while still giving a wide spread with well-filled edges which are easy to hit flying birds with. That only requires about .010" constriction so it actually cuts only .005" deep. Even the thinnest antique barrel wall can stand that. Full choke requires .040" of constriction so the recess is .020" deep cannot be done safely if the barrel walls are thinner than .050", but, fortunately very few are. To restore a useful game choke on a cut-off cylinder bore, modern cartridge gun to be used with plastic shot cups, only 0.010 depth of cut is necessary for about 0.020” constriction. The only way to know for sure is by shooting test patterns, but any constriction improves the pattern otherwise produced from a cylinder bore.
The beauty of a jug choked muzzleloader is that it loads as easily as a cylinder bore.
