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Gunsmithing

Finishing a Barrel

by Patrick Sweeney   |  September 23rd, 2010 1

Lapping the bore with David Tubb’s “FinalFinish” from Moly Coating

This column is about a particular product, David Tubb’s FinalFinish from Moly Coating Inc. One of the last steps a custom barrel-maker does before shipping a tube, or installing it on a rifle, is to hand-lap the bore. Lapping uses a lead slug cast to the bore, impregnated with abrasive and worked back and forth through the newly crafted barrel. The lapping removes miniscule tool marks from the bore with the intent of reducing fouling and improving accuracy.

High-volume production barrels do not get lapped. Most production barrels are more than good enough for their intended use, and the time and cost of hand-lapping is something most deer hunters wouldn’t pay for.

Barrels that haven’t been lapped can sometimes be improved by lapping, but few other than barrel-makers have the proper tools for the job. Fire-lapping a bore, by shooting bullets impregnated with very fine abrasives, has been a subject of experimentation for some years now. The trick is always to get the proper amount of the correct grade of abrasive evenly distributed on a bullet.

For those who haven’t been paying attention, David Tubb has been winning long-range rifle championships left and right for more than a decade now. He has done so well at the National Championships at Camp Perry each year that I hear the match officials are simply going to put photographs of the trophies in Tubb’s rec room on display rather than make him haul them to Camp Perry and back each year. (Just kidding.)

In a competitive endeavor where a few points or a couple of “X’s” can determine the placement of shooters, Tubb won his 10th championship in 2002 with a score of 13 and 20 points, respectively, over the second- and third-place finishers.

In the process of tuning his rifles, Tubb has developed a number of products that even improve things for us mere mortals. The FinalFinish system is one of them and solves the problem of compound selection and its even distribution onto the bullet. Each package comes with 75 bullets in five grades of abrasive. Each grade is selected for correct use and is evenly applied to the bullets. By starting with a coarser grade and finishing with the finest, you smooth and polish the bore.


The idea is to polish the bore for accuracy and reduced fouling. One area you’ll polish is the throat, where the reamer may have left annular toolmarks (circular, around the leade and throat). Also, toolmarks or cutter chatter down the bore can be reduced. Both reduce accuracy by slightly altering the bullet and increase fouling by offering extra friction to the bullet’s passage. In use the FinalFinish system is simple.

First, clean the bore right down to the bare steel. There isn’t much point in wasting the first few shots using the abrasive bullets to scrub out the gunk. Load 10 rounds each of the graded bullets using a load selected from a loading manual or one from the Moly Coatings folks (806/323-9488). Take the loaded ammo, your rifle and cleaning gear to the range.

Fire the 10 shots from the coarsest grade, Compound No. 1. Clean the bore down to the bare steel. Repeat with Compound No. 2, 3, 4 and 5 bullets. The compounds are color-coded so you can sort them out if you mix them up. Darker is finer, but the colors are close, so keep them separated.

Once you’re done, there are 25 bullets left. Those are for the serious rifle-competition shooter, to clean up the throat of his barrel after a season or two of shooting (or, for the cheapskates among us, to treat a second barrel that doesn’t need the most abrasive No. 1 and No. 2 bullets).

I selected as the test for the FinalFinish an AR barrel that I’ve never been particularly happy with. I acquired it from a barrel-maker who subsequently went out of business. It is a 20-inch heavy-contour stainless .223-chambered barrel with a one-turn-in-eight-inch twist. I installed it on a flattop receiver using an aluminum handguard and found it would shoot only 1.5- to two-inch groups.

I can hear someone in the back muttering, “It’s only an AR; what did you expect?” Well, using the same loads, I can get my stock Colt HBar to shoot .75-inch groups and my Eagle Arms (now Armalite) with its match barrel to shoot .5- to .75-inch groups.

When I found I had a bum barrel and that the maker was out of business, I tried everything. I re-crowned it and swapped bolt heads in case the one I was using wasn’t square. I broke it in three times. I swapped scopes. I even dug out an oversize bolt and reamed the headspace to minimum with the new bolt. All to no avail. I even offered it for sale, but I was too honest to fib about its accuracy, or lack thereof, and so no one wanted it.

It has been sitting in the parts drawer for some years now, waiting for this product. I swabbed it out and reassembled it on a flattop receiver. I checked it again, just in case a different receiver would help. (It didn’t.) I had a few questions about using FinalFinish, and a quick phone call took care of my minor worries. For instance, the gas system of the AR isn’t going to be bothered by the compound. Nor would chrome plating (the barrel in question isn’t plated) be a problem. The compound will just polish the chrome.

So I loaded 50 rounds with 21 grains of BL-C(2) loaded too long for a magazine at 2.5 inches OAL but slightly shorter than I normally load 80-grain bullets, to ensure the bullet jumps to the lands. The idea is not to use a standard load, as the abrasive compound will increase chamber pressure. You want a load that will burn evenly enough to give consistent velocities.

SOURCES


Moly Coatings Inc.
801 N. Second St.
Canadian, TX 79014
(806) 323-9488

 

The bullets for .224 cartridges are 80 grains in weight, and 21 grains of powder is a mild load. The only reason for using a heavy bullet is the longer bearing surface gets more compound on the bore.

At the range the shooting was simple. I chambered a round and fired
into the backstop. The instructions said to pay no attention to group size during the process, so I picked out a convenient dirt clod and practiced my hold and squeeze. After 10 rounds it was time to open the action and get out the Shooter’s Choice Copper Solvent and Dewey rod. During the course of the firing and cleaning, I paid close attention to the force needed to press the patched rod through the bore. By the time I had gotten to Compound No. 4, the force was markedly lessened.

And the result? The process didn’t turn my AR into a benchrest rifle, but it did make it shoot better– enough to be worth the cost and effort. The two loads I check accuracy with are Federal Match 69-grain factory and my own load of 24.7 grains of H-322 under a 52-grain Sierra hollowpoint.

This is safe in my rifles, but be sure and work up from 10 percent less in yours.

In the test rifles–my Colt and Eagle–those loads deliver between .5- and .75-inch groups at 100 yards. That is from the bench with sandbags and a Leupold 3.5-10 Vari-XIII. Before the FinalFinish, the “match” barrel would only do 1.5 to two inches. Afterward, the groups were more uniform and between .75 and one inch in size. Would I like better accuracy? Yes, but for the improvement I gained at much less than the cost of a new barrel, I’m happy.

Is the FinalFinish for every barrel? Probably not. If you have a beater brush gun with a cracked stock, fouled bore and loose sights, lapping the bore won’t make a noticeable improvement in accuracy. If you’ve just laid out some serious green for a Shilen XX barrel (as one example) and had an experienced gunsmith with a precision lathe install and headspace it, I’d be very hesitant to do fire-lapping without cause. You can if you want to, but with a pedigree like that, I’d be looking at the shooter as the problem before I’d go blaming the rifle.

  • Michael

    The fire lapping kit enlarges and excessively ruins rifle throats. Folks who make custom barrels lap the bore prior to cutting down the barrel and cutting a chamber. There is no need in doing this to your rifle. Lot's of proof out there all the way back to the 1980's before "tubbs" cashed in on this silly idea. The throats of my rifles deserve better.

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