First a ‘jag’ is made.  Threaded on the left to attach to the lapping rod,  grooved and knurled to securely hold on to the molten lead.

Next a string is wrapped around the threaded end.  This keeps the molten lead from running past the jag down the barrel.

The jag, string and rod are shoved up the muzzle and stopped ~1 inch short of the breech and the whole thing heated to ~400 F.

Any lead overflow is cut off with a sharp knife.  I told you the lead is soft.

The resultant lap is pushed part way out of the barrel for inspection.  Sometimes voids appear due to underheating the barrel or an uneven pour (learning curve).  This is a good one…

Grooves are filed into the lap to retain the abrasive compound.  The lap is coated with the lapping compound..

The lapping rod is attached to a handle assembly (flanged bearing bolted to 1/2″ galvanized pipe with bicycle grips).  The barrel is placed in a sturdy vise.  And the labor intensive part begins.  This will replace rowing machines, eventually…

The lap should not leave the barrel at either end of the stroke.  Otherwise it’s very difficult to get it back in properly.  There is a great deal of resistance at first and each time the grit is renewed.  I could feel differing resistance at certain areas of the bore which eventually became uniform.  After several strokes,  it looks like this..

You can see the rifling.  Note the linear marks from the rifling cutter.  The abrasive has embedded itself in the surface of the lead.

I used 220 and 380 grit on these barrels.  Finer grits are available.  You need a new lap for each grit – no mixing grits!

Here’s the bore after lapping..

And some .457″ balls after passing through the bore..  I lapped more toward the breech end and less at the muzzle.  When passing balls through the barrel,  one can feel them getting tighter at the muzzle.  This constriction is the ‘choke’.

Now,  this process involves HEAT, lead fumes and icky lapping compound.  Not for the average home project..  Just what I’ve done,  not that it’s the only way or even recommended!

~30minutes to make each lap (4 made,  2 per barrel,  1 each for 220 and 380 grits).  ~2 hours of lapping per barrel.

These barrels are almost ready to be inlet into the stocks.  The muzzles need to be lapped,  the breeches filed and polished to seat on the sliding loading bar and secured to the breech blocks.

Later…    Martin

Tapered barrel compared to original in fixture

Three round grooves are cut into the base of the fixture.  The right one clamps a 1/2 inch drill rod to the table.  The left two grooves are used to clamp 2 different rods depending on the taper desired.  This fixture is a large sine bar.  Since I’m machining 2 different length barrels,  2 grooves proportionally spaced are needed.  Two rods are used since the taper doubles as one gets to the fifth side of the barrel.

overall fixture - click pic to enlarge

First side being milled

First rotation of barrel

.125 ” is cut from each side of the muzzle.  The breech has .010″ removed per flat.  The next 3 flats are tapered.

4th cut next

The bronze hammer is used to tap the barrel square into the fixture while tightening the bolts.

5th cut

This rotation places a cut flat on the bottom.  If the slope of the fixture is not changed,  the next cut will be parallel to the bore – bad juju.

The original spacer is on the left.  The thinner spacer is in place under the fixture.  This doubles the slope of the fixture and allows tapering of the next four sides.  The groove on the right is indexed for the taper on the shorter barrel.  The fixture is bolted to the table with T-nuts, studs and flanged nuts in 1 1/4″ diameter counterbores beneath the slot.  A 3/4″ socket is used to tighten the nuts.

Final cut - muzzle

One reason such care was made in the manufacture of this jig,  is that the X-axis travel of my mill is less than the barrel lengths.   Each flat had to be cut from the muzzle to the end of travel,  the barrel shifted, the cutter re-indexed and the cut finished from the breech.  It could have been done between centers,  with a spin jig or an indexing head.  These would be prone to chatter and require multiple passes.  The rigidity of this fixture allowed a full .125″ cut on each flat.

breech overhang

Breech positioned and cut

A Kool-Mist minimum lubrication system is seen in these pix.  Approx. 1/2 gallon of fluid was used to fabricate the fixture and mill both barrels.  Clean up is quick and simple due to the minimal fluid used.  The system is very effective and allowed both barrels to be milled with one endmill resulting in a good surface finish.

Barrel comparison with rifle - click to enlarge

Total time 6 hours with photography.   It took more than 8 hours to build the fixture and cut a test barrel from a cutoff.

Hope you enjoyed this post.   Later,    Martin

Built a new rifling head and cutter for the Girardoni rifle barrels.   The design is modified from “The Modern Gunsmith” by James Virgil Howe.  His design is based on a scraper rather than cutter as used on the 1902 Springfield rifle barrels.  It operates/cuts in both directions.  I’ve made a carbide cutter and Ag brazed it into the rifling head.

The head is placed on a rod affixed to the rifling machine and inserted into the breech of the barrel.

After pushing and pulling the head/cutter through the barrel,  a very fine swarf is produced.   The swarf resembles steel wool and is difficult to see and remove from ones skin.

The original Girardoni has 12 grooves and lands with a .463 groove depth.  We are going for a .457 depth due to the availability of that caliber ball and molds.

Two Green Mountain .45 smooth bore, 1″ octagonal barrels were purchased.  They have been rifled,  cut to length,  breeches reduced, threaded and indexed to fit into the breech blocks.   One is stock length,  the other 4″  longer.  Having seen Dr. Beemans replica,  I think a longer rifle might look better IMHO.

Time:  4 hours on the first barrel, 3 hours on the second.   Learning curve.

Next step will be to taper the barrels.  They will taper from .980″ to .750″,  breech to muzzle.

A rack and pinion are affixed to a diagonal track (adjustable) and a linear carriage.  The carriage houses the pinion gear and is rotated by the rack as they move up and down the I-beam.  Since the rack can move in and out of the carriage,  due to the angle of its track,  the rifling cutter can be rotated to give a precise and repeatable twist rate.

The following pictures demonstrate  the machine and rifling head as used for 2 of the Lukens barrels.  I’m presently making the rifling head for the Girardoni rifles.

Rifling machine

Here is the end view of the machine.  The main frame is a 4″x4″ Al I-beam.  The diagonal to the right is the sine-bar and is Al channel.  These elements have linear guides attached for smooth travel.  The Al clamp and rod closest to us is an end stop, adjustable for barrel length and twist.  The next assembly is the carriage containing the rack and pinion.  At the far end resides the barrel vise and indexer.

Carriage disassembled

Here are the guts of the carriage.  From left to right:

Carriage housing with linear guides at bottom,  needle bearings pressed into bore and rack support extending to the right.

Pinion gear with torrington thrust bearing.  The gear has a 1″ diametrical pitch,  therefore 3.1416 ” of  rack travel gives 1 revolution of the cutter.

Bronze bushing to seat gear and adjust endplay.

The rack is at the bottom of the picture.

Linear guides and tracks

Here are the guides and tracks of the carriage.  Note the rack passing through the carriage and the diagonal sine bar in the background.

Inside carriage

Underside of carriage with pinion gear installed.  The groove for the rack is visible as is the uninstalled rack above.

Teflon rack guide

Here is the rack and its teflon guide assembled on the gear.  The bottom 0f the carriage is ready to be attached.  The central hole in the carriage base has a set screw to adjust clearance of the rack and pinion gear.

skinny view

Here is the carriage assembled without the rack to show the relation of the gear, track and teflon rack guide.

Carriage assembly

Top of assembled carriage.  Tapes are glued to the track and rack guide to allow setting the twist rate.  Here we are at 40″ of twist.  A length of grey PVC pipe estends to the left to protect the extended rack.   Below,  the end stop is set for the barrel length.

Barrel vise

At the other end of the machine is the barrel vise.  Two pillow blocks support a length of 1.5″ tubing.  At each end, four  screws secure the barrel concentrically in the tube.   To the right is the indexer to select nunber and position of the grooves to be cut.

Indexer

The indexer has three rows of holes (7, 12 and 15  positions) to allow any where from 1 to 7, 12 or 15  grooves to be cut in a barrel.  The holes are selected by the black springloaded plunger which can be clamped inline with the requisite row.

Since the machine is primarily aluminum, it is easily moved and stored.  Here I am lifting it ~50 lbs.

The disassembled riling head.  The tube is above into which is inserted the cutter and wedge.  A tapered pin retains and acts as a pivot for the cutter.  The o-ring acts as a spring to drop the cutter when the  wedge is retracted.  The adjusting rod extends to the right and allows the cutter to be raised and lowered.

Closeup of the cutter and wedge.

Cutter raised and lowered.

Here are some balls showing the rifling (.32 cal – Lukens).  Three shots @ 25 yards.