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There are break-in procedures, and cleaning with JB or Iosso Bore Cleaner will get them to progress a little better than just patches and solvent, but they don't truly lap the bore.

For true lapping you have basically two alternatives: hand lapping and firelapping. The first normally uses a lapping slug on the end of a cleaning rod that is cast into the muzzle of the bore by plugging the bore back an inch or two with patches or paper and pouring molten lead into it. Grooves similar to lead bullet lube grooves are cut into the cast slug with a knife or a gouge to hold abrasive compound. The lap is loaded (the grooves filled) with abrasive and run back and forth in the bore by hand. It's s common to use something like 320 grit silicone carbide lapping compound (Clover compound, for example). The slug is usually pure lead so that when it encounters a constriction it is narrowed and does not spring back out after passing through it. In this way all abrading on subsequent strokes is only in the tight spots. When you feel it stop cutting tight spots, you can bump the lap back up with a brass rod and hammer, and go at it some more. You keep repeating until the bore has no more tight spots and the lap feels smooth down the length of the bore.

The other method is firelapping. This involves shooting abrasive embedded bullets through the bore with very light loads that get low airgun velocities (300-500 fps). The lapping bullets are usually cast bullets in the hardness range of 10 to 12 BHN. This number range is a compromise. It doesn't limit itself to cutting constrictions as completely as pure lead laps on a rod, but it is malleable enough that it doesn't lap the wide places nearly as hard as the narrow ones. The reason it isn't pure lead is that where a pure lead hand lap can be pushed through a constriction by rod without bumping up, when you have even firelapping load pressures on the base of a pure lead bullet it will bump up to rub the wide spots as well as the narrow ones. At the other extreme, an alloy bullet of higher BHN is surprisingly elastic and will go tightly into the bore and stay tight all the way down its length, thorough narrow places and wide ones. That tends to remove material evenly everywhere. You don't want that because, while it widens tight spots, it widens wide places equally, so you don't level off major irregularities; you just smooth those shorter than the length of the slug. When you are done firelapping, irregularities are gone and it leaves the bore very slightly tapered down toward the muzzle. Maybe a half thousandth or so. This is considered desirable for accuracy, especially when the bore is to shoot lead bullets.

Either lapping method will reduce metal fouling, making the bore easier to clean. Firelapping has the advantage that in addition to introducing the slight taper, it also cleans the throat up. Hand lapping does not normally clean the tool marks off the throat because the rifling is cast into the slug when you pour the lap.

The board sponsor, Beartooth Bullets, sells a firelapping kit, here.

technical note (and I hope I haven't posted this already)... some barrel makers have their own "lapping" procedure. If you have a Kreiger barrel, it's best to read their thoughts on their barrels. I normally use Kreiger when I can. Got 2 M14 barrels on the shelf.
 

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was wondering as a kid me parents bought colgate powder, is that what you use for lapping or colgate tooth paste? thanks
 

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A concern I have with firelapping is possibly too much lapping of the throat. The barrel portion I think poses no issue at all since the lead bullet evenly obturates the rifling land and grooves, but I wonder if the lapping at the throat is more aggressive since the bullet is transitioning at that point and thus shortens barrel life as a result? Anyone have any thoughts about that? Some lapping of the throat might actually be beneficial to clean up tooling marks and irregularities though. I wonder if after doing an initial portion of the firelapping process, instead of loading the lapping bullets up with lapping compound prior to shooting, just leave them plain and instead deposit a light swab of lapping compound for the first several inches of the barrel just beyond the throat. Seems like that would avoid excessive wear on the throat beyond some initial dressing with the first lapping loads, but still lap the rest of the barrel until all restrictions had been removed and the bore polished. I suppose one concern doing that would be to not overload the bore with lapping compound and have the right load velocity to keep the bullet from plugging the barrel? Before and after firelapping, making a cerrosafe casting of the chamber would provide an interesting look at the difference in the throat from the firelapping process.
 

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My comment really was just generally speaking MikeG. However, I did buy the Beartooth lapping kit years ago when I bought my first 444 Marlin. I haven't used the lapping kit yet because I thought about the possibility of excessive throat erosion after buying it. But I may still lap it. Wish I had a borescope. It would be handy to monitor the lapping progression.
 

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I haven't seen any substantial throat erosion in 20 lapping rounds, and that is generally about what it takes to do the average Marlin. Pushing the throat forward a little might not be a bad thing with Marlins, either.

My opinion.
 

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This is news to me. I have not done any cases with cream of wheat, but many of the bench guys that do it alot use that stuff! That's what I have read anyways. Wouldn't the polyester fibers melt in your barrel and cause some nasty "plastic" buildup in there?
Dacron will NOT melt. I pick it up on the range. Just dirty. Plastic wads do not melt and paper wads don't burn. I put newspaper wads over flash holes and they get black and dirty but don't burn and need picked out of brass.
Cut barrels were commonly lapped by hand. New barrels are smoother but fire lapping can help. Done right and only rough spots get smooth with no wear.
 

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A rough bore is not real bad except for fouling pick up. I had a TC Tender in 30-30 with a terrible bore. I sent the barrel back and the new one was as bad. It did not stop me from shooting penny's and nickles at 100 yards from a rest. I shot cast from it since copper would build up bad.
 
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