On the topic of hand lapping a new, or used for that matter, barrel what is the proper procedure.
This was sent by Gale McMillan over a decade ago and it still applies today. This is in the context of a rough barrel bore. You could ruin a custom barrel if you attempted to alter the bore finish imparted by the maker, and you could ruin a good barrel if you attempted to lap the bore without a proper lap. It is impossible to lap a barrel evenly without the use of a poured lap as you would remove material unevenly and would round the rifling causing excessive wear in the areas you do not want to alter. Attempting to lap an installed barrel, would in addition, wash out the muzzle and breech ends. This is Empirical data collected from years of experience via top-end barrel makers and not from the use of a placebo effect. Quite a number of rifles such as the LTR noted in this thread will shoot very small groups when properly broken-in with a layer of hard carbon burnished upon the bore. Quite a number of the same rifles will open up if copper jacket material is allowed to stick and build upon itself. Simply removing this build-up will restore accuracy having nothing to do with home-brewed lapping. Quite often people think they are lapping when in reality they are only cleaning aggressively while accelerating wear.
From Gale reference a rough barrel:
�Run an oily patch through the bore first. To make a lap you can use an old cleaning rod. Wrap masking tape around it just behind the jag until it fits into the barrel tightly and will hold the rod in place when the barrel is held vertically. Pull it back into the barrel about 6 inches from the muzzle. Heat a lead ladle full of lead until it is very hot, it can be turning red and work well. Hold the barrel by the muzzle with your hand 6 inches below the end and tilt the barrel at an angle so that any overflow will miss your hand as it falls. Pour the lead as fast as you can without spilling so that it doesn't cool as it runs down the barrel. When the barrel is filled, let it cool, and bump it out about an inch and then carefully trim the end off so that it can be drawn into the barrel. Bump it out about three inches and pour oil all over it. At this time put masking tape at the breach end so that you can use it as a gage to see how far to push it out, then measure the barrel and when you have pulled it out the length of the barrel put another round of masking tape so you can tell how far to pull with out pulling it out of the barrel. Push it out of the barrel and oil it and put a very small amount of lapping compound on it and draw it through the barrel a few strokes and add a little more. It is better to go real slow with the amount of lapping compound rather than get the lap stuck in the barrel. Keep oiling the lap and charge it when it gets easy to pull. Its all a matter of feel. Use 220 grit clover leaf non imbedding lapping compound. It goes without saying that you hold the barrel in a vice while lapping. Lap it full length until the lap frees up and charge it with a little more compound. Lap it a few strokes and remove the lap and clean the barrel and look at it. You don't want to remove a lot of material, Just enough to clean it up. Clean with solvent and brush when finished. When using a 6-8 inch poured lead lap on the end of a cleaning rod to lap with, it will indeed increase the diameter at the point at which you change directions, this is almost always the breach and the muzzle. You never lap an installed barrel except as a last resort!� - Gale McMillan
This is an excerpt from an article written by Dan Lilja on barrel fouling and break-in around a decade ago. It also applies here:
�Makers of custom hand-lapped barrels spend a lot of time achieving the internal finish that they require. We've experimented with different techniques and products and have settled on what we believe gives us the best finish. We strive to get a smooth uniform finish without losing the geometry of the rifling -- that is, keeping the lands sharp-cornered and crisp. And though it may surprise some, lapping to a finer finish will result in an increase in fouling. A barrel can be too smooth.
It is important to break-in a barrel though. The jacket material must be removed after every shot during the initial few rounds. If this isn't done the areas of the barrel that fouled will tend to pick up more fouling and it will build on itself. It is important to get a layer of powder fouling on top of the lands & grooves. This hard deposit will prevent the copper from stripping off the bullets. However, if the internal finish of the barrel is too rough the barrel will never be completely broken-in and fouling will always be a problem. Some barrels can't be broken-in.
A similar phenomenon can exist if the shooter uses an abrasive-type cleaner too often. The abrasives are very effective at removing all traces of both powder and jacket fouling. I mentioned that a barrel can be too smooth. The abrasives can get a barrel too clean as well and in effect the shooter is rebreaking-in the barrel again every time he cleans. This can end up in the dog-chasing-his-tail scenario. The shooter thinks the barrel is a fouler, as evidenced by the copper accumulations in the barrel. He works hard at removing the copper, resorting to using an abrasive cleaner. But when he does he removes the desirable layer of carbon fouling left by the powder and exposes fresh steel ready to grab some more copper off the bullet on the next shot. The cycle repeats itself. Like the dog the best way out is to go lay down and take a nap.� - Dan Lilja
My advice would be to refrain from running the barrel temps through the roof from excessive rapid shots. Keep jacket fouling in check and allow the bore id to burnish with a hard layer of carbon fouling. Maintain the barrel to prevent rust without stripping the bore down to bare steel. Use the least aggressive methods possible to keep fouling in check. Shoot the gun and allow the bore to break-in without inducing accelerated wear from aggressive means. If you feel the need to lap a rough bore, do so correctly by pulling the barrel.
Best:)