I’ve been re-cutting or freshening the rifling on original and modern ML barrels for a while now and continue to learn what’s easy, what’s hard, and how to deal with what’s hard.
really small calibers are hard
My process is to make a hickory rod very close to bore size, file a square portion near one end, and cast a lead lap. Then I make and inlet cutters for land and groove on opposite sides of the cutter. Well, if we are starting work a .32 caliber we have a puny rod starting out and after filing a square and inletting the cutters it’s pretty weak. Calibers .36 to .40 are tough but easier. Anything .45!or greater is stout and no issue.
Forget about button rifled modern barrels. . These are so surface hardened that there’s no cutting them with simple cutters. So leave out TC’s, Lyman’s, Spanish and Italian hallow groove rifling.
if the rifling is not intact in the powder chamber all the way to the breech, it’s a long slog . Until you’ve examined originals it’s hard to imagine how bad some bores are shot out. One are 0.020” or more oversized ahead of the breechplug. This is why many original barrels were trimmed at both muzzle and breech when the rifling was recut. I resurrected one original barrel of my own and grew the bore over 0.025”. Probably 30 hours and 2 rods and 5 laps poured.
they sure used narrow grooves back in the day. I see a lot of barrels from the percussion era with grooves under 0.075” wide. Interesting.
most percussion era barrels I’ve handled are “coned” at the muzzle. . I’m not sure how or why they did it but most run 0.010 to 0.015” oversized at the muzzle. This makes pouring a useful lap problematic. It will not go down the bore at all. In suc cases I file the lap to the diameter it is 2” into the barrel, oil it, pound it in a half inch, bring it out, carefully relieve it in grooves and lands using chisels, and repeat till I have a slug that will go all the way down the bore AND has good groove impressions.
On a rough bore I cut grooves deeper before touching the lands. . I feel that getting the grooves cleaned up is job #1 and I can then be sure that the groove cutter will track well.
a slightly rounded groove cutter tracks better in weak rifling. . Getting a square edged cutter to track in pitted, rusty grooves is quite challenging. A little radius on the edges helps.
Setting the cutter at a very slight angle helps. One would think you’d want the cutter perfectly parallel to the bore so all teeth are cutting. But if the end entering the barrel is 0.001” or 0.002” lower the cutter will slide into the groove and index well. We are relying on the existing grooves to guide the cutter, not a rifling bench. Once inserted the pressure will square the cutter up nicely.
Non-uniform tooth spacing on the cutter prevents chatter. I’ve seen several barrels that were freshed at least once, maybe 10,000 rounds before they ended up as they are now. They sometimes have chatter in the grooves and lands. To overcome or prevent this I file cutter teeth at a slight angle from 90 degrees from the bore and space them unevenly.
Once the groove cutter is cutting almost end to end, its time to cut lands simultaneously . Lead us soft and the lap the cutters are inlet into are compressible. To prevent problems while just cutting grooves, I inlet a piece of brass opposite the groove cutter, where the land cutter will eventually go. This rides nicely on the lands and allows the groove cutter to really cut and not compress.
Strategy for setting desired groove depth Obviously one needs to cut grooves and lands until all pits are gone and it is of uniform diameter end to end. But one may find the grooves are then deeper than desired. I then use a dummy brass piece where the groove cutter is inlet, to both track the groove and resist force from the opposite land cutter.
Land cutters radius. The land cutter needs to bd rounded on top and ideally at a radius slightly under bore diameter. I see barrels that were the-cut in their working life that had lands cut with square cutters. Not sure it matters but the rifling then looks polygonal rather than grooves in a round bore. Supposedly if the tops of the lands have a radius slightly under bore diameter, the edges of the lands grip better. May be imaginary but that’s what some old timers have told me. I take a drill that goes easily into the bore, drill a hole in a piece of steel, and line the land cutter’s rounded top edge with that. Eyeballing it is not in my skill set yet.
Deep teeth hold more shavings. I guess one could hand file shallow teeth but they will jam up with the shavings pretty quickly. So I leave plenty of depth and distance between cutter teeth. When cutting 0.015” in a groove 46” long, a lot of tiny shavings are produced.
Ok, that’s what’s fresh in my brain. If you have tricks of other approaches, please share or debate! Done on phone with old eyes so some auto spell errors are expected.
