Firelapping For Accuracy

Guns Magazine, August, 2001 by Charles E. Petty

Got a rifle that's giving you trouble? Before you spend money on gunsmithing, try this simple but effective accuracy-tuning procedure that's as easy as a trip to the range.

The idea of using an abrasive compound to polish the inside of a rifle barrel is hardly new. The practice of lead lapping certainly dates to the early days of centerfire cartridges and perhaps even further back into the days of muzzleloaders. The concept is actually pretty simple. A steel rod is inserted from the breech end of an unchambered barrel and stopped an inch or two from the muzzle. Then, molten lead is poured into the bore to form a lead slug.

Once the lead sets up, the rod is pushed out of the muzzle and the lead slug is coated with a mix of oil and lapping compound. The slug is then pulled and pushed back and forth through the barrel.

When you do this, even with a very well made barrel, you can actually feel differences in resistance as the lap goes through. Spots that are tight may get a little more attention. It is a job that requires a certain skill.

Depending on the condition of the original barrel, the lapping process can be easy or difficult. The grit of the lapping compound is a matter of choice and there are differing opinions, but most use medium or fine grades. Sometimes a barrel will receive treatment with several different grades, ending with a very fine compound.

The entire process of lead lapping is accepted as beneficial and is often done to the more expensive custom barrels. For example, the rifles that come out of Remington's Custom Shop wear hand-lapped barrels. It is also possible to have it done by machine, although this loses the feel that a skilled maker uses to know when a specific spot in the bore needs a little extra work.

Abrasive Talk

Most shooters view abrasive compounds with the thought that they should never be in close proximity to a firearm -- and that is generally true. But lapping compounds can be wonder tools if used properly, and the new firelapping process offered by Neco is truly a wonder.

Back in the old days it was possible to get a wonderful slide-to-frame fit on a 1911 with the judicious use of fine valve-grinding compound bought at the auto parts store. Today there are a plethora of compounds in grits ranging down to micron size (1 micron=0.000001 meter). Neco uses laboratory grade aluminum oxide compounds because of their greater uniformity.

But when we talk about shooting something through the barrel of a rifle, the auto parts store is not the place to go. Just a drop of oil on a bullet can raise pressures substantially.

Neco's bullet coating process has no such concern because the lapping material is imbedded into the bullet and is completely dry. Even so, shooters should use reduced loads to provide an extra margin of safety.

You have several choices in how to firelap a barrel. Neco sells a kit with everything needed to coat your own bullets, you can purchase pre-coated bullets or purchase specially loaded ammo ready to shoot. The latter was the approach here, even though it is the most expensive option. It is also the quickest.

The box of cartridges contained 30 with bullets embedded with coarse (220 grit); medium (400 grit) and fine (800 grit) lapping compounds. There are also 20 "polishing" rounds coated with 1200-grit compound. This is enough to treat at least two rifles.

The test began with a thoroughly cleaned bore, which was then examined carefully using a bore scope. There were definite tool marks and several inclusions where chips left over from the reaming operation remained in the bore during hammer forging. This left crevices that looked something like the Grand Canyon with the bore scope's magnification, although they were actually quite small. The most important thing was to get a subjective impression of the smoothness, which really wasn't bad.

For the test to be valid it required getting a good baseline accuracy result before treatment. We used Black Hills ammo loaded with a 50 gr. Hornady V-Max bullet, since our experience with this ammo has been very good. Five, five-shot groups were fired at 100 yards with the rifle carefully bench rested. A Bausch & Lomb 6-24x scope was used, set on the highest magnification.

The test plan required firing two fouling shots through a cold, clean bore followed by three groups. The bore was then thoroughly cleaned, fouling shots fired, and two more groups were fired for a total of five. The average of those groups was 1.237".

The Lapping And The Slugging

After test firing, the bore was cleaned using an Outers Foul Out and inspected with the scope to determine that it really was spotless. Neco recommends pushing a lead slug through the bore at each step to subjectively evaluate smoothness, the amount of work required to push the slug through and to feel for obviously tight or loose areas. Before the lapping began, slugging revealed tight areas just forward of the chamber and again near the muzzle.

Firelapping was started by firing the first five bullets with coarse coatings. The bore was cleaned and inspected for changes. We found a little visible polishing. The passage of the lead slug was a bit easier.