How To Lap A Rifle Barrel

September 23, 2010

Lapping the bore with David Tubb's "FinalFinish" from Moly Coating

By Patrick Sweeney

This cavalcade is about a particular product, David Tubb'southward FinalFinish from Moly Coating Inc. One of the final steps a custom barrel-maker does earlier shipping a tube, or installing information technology on a rifle, is to paw-lap the bore. Lapping uses a lead slug bandage to the diameter, 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. About production barrels are more skillful enough for their intended use, and the fourth dimension and cost of hand-lapping is something nigh deer hunters wouldn't pay for.

Barrels that haven't been lapped can sometimes exist improved past lapping, but few other than butt-makers have the proper tools for the job. Fire-lapping a diameter, past shooting bullets impregnated with very fine abrasives, has been a subject field of experimentation for some years now. The play a trick on is e'er to become the proper amount of the right grade of abrasive evenly distributed on a bullet.

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

In a competitive effort where a few points or a couple of "X's" can decide the placement of shooters, Tubb won his 10th championship in 2002 with a score of 13 and twenty points, respectively, over the second- and third-place finishers.

In the procedure of tuning his rifles, Tubb has developed a number of products that even better things for us mere mortals. The FinalFinish arrangement is one of them and solves the trouble of compound selection and its fifty-fifty distribution onto the bullet. Each bundle comes with 75 bullets in 5 grades of annoying. Each grade is selected for right utilize and is evenly applied to the bullets. By starting with a coarser grade and finishing with the finest, you lot 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 take left annular toolmarks (circular, effectually the leade and throat). Likewise, toolmarks or cutter chatter downwardly the diameter can exist reduced. Both reduce accurateness by slightly altering the bullet and increase fouling past offer extra friction to the bullet'southward passage. In utilize the FinalFinish system is uncomplicated.

First, clean the diameter 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 1 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 form, Compound No. ane. Make clean the bore down to the bare steel. Repeat with Chemical compound No. 2, three, 4 and 5 bullets. The compounds are color-coded so you lot tin sort them out if you mix them up. Darker is effectively, but the colors are close, so go along them separated.

Once you're done, there are 25 bullets left. Those are for the serious rifle-competition shooter, to make clean upwardly the pharynx of his butt after a season or two of shooting (or, for the cheapskates among u.s., to treat a 2nd butt that doesn't need the most abrasive No. 1 and No. two 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 later on went out of business. It is a 20-inch heavy-contour stainless .223-chambered butt with a one-plough-in-eight-inch twist. I installed it on a flattop receiver using an aluminum handguard and found it would shoot simply 1.v- to ii-inch groups.

I can hear someone in the back muttering, "It'southward simply an AR; what did yous look?" Well, using the aforementioned loads, I tin can become my stock Colt HBar to shoot .75-inch groups and my Hawkeye Arms (at present Armalite) with its match butt to shoot .5- to .75-inch groups.

When I establish I had a bum barrel and that the maker was out of business, I tried everything. I re-crowned it and swapped commodities heads in case the ane I was using wasn't square. I bankrupt it in three times. I swapped scopes. I fifty-fifty dug out an oversize bolt and reamed the headspace to minimum with the new commodities. All to no avail. I even offered it for sale, simply I was as well honest to fib well-nigh its accuracy, or lack thereof, and and then no i 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 instance a different receiver would help. (Information technology didn't.) I had a few questions about using FinalFinish, and a quick telephone call took care of my minor worries. For instance, the gas system of the AR isn't going to be bothered past the compound. Nor would chrome plating (the butt in question isn't plated) exist a problem. The chemical compound will just polish the chrome.

Then I loaded l rounds with 21 grains of BL-C(2) loaded too long for a magazine at 2.5 inches OAL just slightly shorter than I ordinarily load 80-grain bullets, to ensure the bullet jumps to the lands. The idea is not to utilise a standard load, as the abrasive compound will increase bedchamber pressure. You desire a load that will burn down evenly plenty to give consistent velocities.

The bullets for .224 cartridges are lxxx grains in weight, and 21 grains of pulverization 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 unproblematic. 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 skillful my hold and squeeze. After ten rounds information technology was fourth dimension to open the action and go out the Shooter'south Selection 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. Past the time I had gotten to Compound No. 4, the force was markedly lessened.

And the result? The procedure didn't plough my AR into a benchrest rifle, but it did make it shoot better-- enough to exist 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 nether a 52-grain Sierra hollowpoint.

This is safe in my rifles, simply exist sure and piece of work upward from 10 pct less in yours.

In the test rifles--my Filly and Eagle--those loads evangelize betwixt .v- and .75-inch groups at 100 yards. That is from the bench with sandbags and a Leupold three.five-10 Vari-XIII. Before the FinalFinish, the "lucifer" 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 similar improve accuracy? Yeah, 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 croaky stock, fouled bore and loose sights, lapping the bore won't make a noticeable improvement in accuracy. If y'all've only 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 burn down-lapping without cause. You lot can if you lot want to, only with a pedigree similar that, I'd be looking at the shooter equally the trouble before I'd get blaming the burglarize.

Source: https://www.rifleshootermag.com/editorial/gunsmithing_finish_0723/83432