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Old May 25, 2012, 09:55 AM   #19
Join Date: March 4, 2005
Location: Ohio
Posts: 13,720
Yes, they are lapped, but I think the folks who first came up with the concept of break-in were benchrest shooters with lapped barrels. Gail McMillan always insisted it was a waste of good barrel life, but I did an experiment while firelapping an old military barrel that suggests that's not 100% the case. As the abrasive-loaded bullets I shot through that barrel became finer than normal lapping abrasive (400, 800, and 1200 grit), I stopped after each set of lapping bullets and cleaned thoroughly then fired ten regular jacketed bullets. I then counted the number of patches of it took to clear the last trace of copper. As the abrasives got finer and finer and the bore was more and more polished, the patch count kept getting lower and lower. So there does seem to be some cleaning advantage to further surface polishing than the as-lapped bore usually has. I think that's what Varmint Al has found, except that, unlike my firelapping (which I would not do to a hand lapped bore), he feels the Flitz usually does well enough to achieve that same result in a lapped bore.

On the other side of the coin, I've seen the argument made that if you over-polish a barrel it can take longer to settle because the carbon fouling doesn't reach accumulation equilibrium as quickly. The old rule of thumb was that if you changed powders in the middle of a match it would take 10 rounds for the fouling to re-equilibrate to give best performance consistency. The over-polished theory suggests that would take longer with a really smooth bore. I have not proved this idea in anything I shoot, but I'm not shooting benchrest guns. I note that G. David Tubb's Final Finish system leaves a highly polished bore and he's found that polish an advantage in non-BR match shooting.

One thing that didn't pop into my head right away regarding this whole thread is that the Lapua Scenar Silver bullets are moly-coated. I would not use a coated bullet for break-in. If you subscribe to the idea that break-in will burnish the surface, you want the greater friction of an uncoated bullet for the task. Otherwise it will take more rounds to do the job; maybe many more. You also want to avoid having moly pack the microscopic surface imperfections you are trying to burnish over, as that might actually interfere with burnishing. Boretech makes the best moly removing cleaner I've tried, and I would suggest cleaning with that to remove moly, then using either their Eliminator or their C++ product or KG-12 to clear copper traces, then break in with jacketed bullets. The cheapest commercial ammo you can get should be fine for the task. I would use a light bullet load as the heavier ones often don't bump up to fill the corners of the lands as well.

Howa's U.S. distributor recommends using Windex to clean any traces of hydrocarbons from the bore before firing each additional break-in shot. They offer the theory that you should fire ten rounds with cleaning like that between each shot and also five minutes cooling between those shots. They claim that causes the barrel to tend to take a set in the cold bore position, so that it won't tend to walk as it heats up in later firing. Their procedure is here. I don't have proof they are right about this, but ten shots is a pretty tame quantity to invest. They claim most of the copper wash fouling has stopped being left in the bore after round 6 or 7 by this method. They then go on to fire another ten in pairs between cleanings. I've never understood that idea. I'd clean between each break-in shot to better expose the bore to the burnishing. But they also say that is just insurance that burnishing is complete. They seem to think they were really done at 6 or 7, if I am reading them correctly.
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