Barrel Lapping Technique

The throat of the rifle gets jugged if you apply any coarse grit to a bullet.

Normal fire lapping cuts the chamber end vastly more than the muzzle end. The grit is used up in a few inches of high pressure lapping. The below technique solves the problem.

Patented technique (joking for the humor impaired).

You will dedicate a cleaning rod to this, do not use this rod on anything else!!

1. Make sure you have a muzzle centering device on the cleaning rod, you will need it. Some kind of disposable gloves are mandatory, or wash your hands between grits so as not to transfer coarse grit during a finer grit stage.
2. Make a clamp that will not slip to attach as a length stop for the cleaning rod.
3. Figure out where the chamber lead ends, either by measurement, math, knowing the reamer, or, for you dirt sucking hillbillies (like me), close the bolt on a dummy round in the chamber, run the cleaning rod with the brush you will be using down the barrel until you hit the bullet. Tighten your clamp 1/4 shorter than this distance.
4. Roll the cleaning brush in a hard oil based cutting compound (Brownells sells all but the coarsest grit in large tubs). Spray the grit loaded brush with some light oil to make the grit very wet. Push the rod in to the stop, give it 2-3 quick spins to transfer grit, then take 4-6" strokes back, 1/2 strokes forward until you are back out of the bore. Use a bore light to inspect to make sure you have no lumps, and all grit is evenly distributed.
5. Fire 1 round. Repeat as needed. Before changing grits, fire 3 rounds.
6. Leave the brush with the lapping compound. Fully clean the rod, change your gloves.

Ideal (-ish) round count is the following (everything loaded to ~~1300 fps in jacketed, 800 fps in lead). You want the longest bearing surface bullets you can find.

Silicon carbide grit works great for this.

• 300 grit. 0-8 rounds, depending on how bad the bore is.
• 600 grit. 4 to 5x the number of rounds in the previous step. Typically 10 rounds
• 800 grit. 2x the previous step, ~~20 rounds
• 1200 (or 1000) grit, 2x the number of rounds in the previous step. Typically 40 rounds
• ---- Clean the barrel, the rod, everything for this next step----
• Fire ~50-80 rounds using 2000 garnet. JB bore polish is ~1600 by actual measurement, and will do in a pinch.

Now, this is the tricky bit. Apply JB or 2000 garnet compound to just the ogive of the bullet. If using lead bullets, you can coat the whole thing, including the lube grooves. Lead bullets are much preferred for this step.

With great care, slide the cartridge fully in the chamber, DO NOT TRANSFER ANY GRIT TO THE CHAMBER WALLS! I made a tube that closely fits the cartridge, and in an AR or bolt gun that is used to guide the round into place with no grit transfer. This will polish the throat, without opening it up too much, or lengthening it more than ~0.005"

Fire 10-50, or until you run out of daylight.

I've turned a factory Ruger 10/22 barrels from 1.5"-2" at 25 yards into shooting into the 0.1x" using TenEx. From a machine rest, the best groups I've gotten from a 77/22 are 0.035"-ish consistently. In a 10/22 0.080" These were using the Optimal Twist barrels I used to have.

I took a friend's 30 TC rifle that was shooting 3" at 100yards, and in about 2 hours, got it to 1/4" with handloads.

For chrome lined barrels, use diamond compound. The coarse compound is _VERY_ expensive. Don't do what I did and mis-understand how grits are calculated for diamond grits, it is not the same standard as normal lapping compounds. I wasted ~800 rounds and $300 on diamond lapping compound that the coarsest grit was 30,000. Woops.

Once we got it right, about 300 rounds later, the barrel shot below 0.15" (IIRC) with ammo that was hand fed, and into the 2's (?) from the magazine. No I was not behind the trigger, my friend Dick was a benchrester, and fiddle-fucked with that gun for 3 months before he was happy with the forend and the trigger. He taught himself to stone ar-triggers for this test. IIRC the pull was < 1 pound.