Grease and lubricant raise pressure if not carefully used. Carbon hardens as it ages, so wear on the barrel is increased when shoving old carbon down the tube as opposed to fresh warm carbon (read Humpy's post, here
). Finally, most guns need several shots of fouling to settle. Target shooters have noted that if you change powders in the middle of a match it can take 10 rounds before the bore really settles. You don't know what powder the manufacturer fired through it, so you'd be buying the extra work of re-settling if you left old carbon in it. Finally, the Howa distributors claim to see evidence that hardened carbon in the surface imperfections and tool marks of a new barrel can promote heat walking and they recommend a break-in procedure they claim avoids that by careful firing and cleaning for at least each of the first 10 rounds (which they follow up with another 20 cleaning alternate rounds, but, IIRC, they don't claim that really does anything; seems it more like makes them feel better).
I can't quantify the merits of any of the above ideas and observations any better than that. But if I take Humpy and Howa or even just one or the other at face value, it seems prudent to really get all
the carbon out before using the barrel further, even out of the "pores" of the metal (metal is not porous, but some surface imperfections, tool marks, and grain boundary corruptions resemble pores in an electron microscope). I then use the Howa distributor's method for the first ten rounds to see if that really helps avoid heat walking, and so far so good.
Toward that end, I've recently adopted what I think of as aggressive pre-cleaning of any new or used barrel I have occasion to work with. The first thing I do is pull the gun out of its stock and remove any grip panels to avoid solvent damage. I also get a good look at lubrication and interior cleanliness to see if I need to detail strip and clean it.
The next thing I do is use a small pump sprayer to wet the bore and chamber with Boretech Eliminator. This is, IMHO, the best of the jack-of-all-trades cleaners. I let it sit 15 minutes and all that lets me patch out all the surface fouling and a lot of copper fouling is removed by it, too.
I repeat the above, and if much blue comes out on the second pass (use a plastic jag, as a brass one turns it blue), I run a dry patch then a couple of patches wet with Windex followed by a couple of dry patches to remove the Eliminator, and then apply KG-12 and let it sit 15 minutes to get the rest of the copper. I then use a dry patch followed by Windex followed by a dry patch or two again to remove it.
At this point I have a look with a bore scope. If I see any copper, I will repeat with KG-12, but thus far I have not. If you don't have a bore scope, you can repeat with Eliminator to see if any blue appears, then wash it out with Windex and dry patches. KG-12 has relatively little color change as it eats copper, only getting a deeper orange tan. It's hard to tell much from its color.
If the barrel was ever used with lead bullets, at this point I apply No-Lead and let it sit an hour and patch it out. Again I use the dry patch, Windex and dry patches for removing the cleaner.
Now the carbon removal gets serious. I plug the chamber with a chamber plug (or with a Neoprene stopper if I don't have the right size chamber plug), and then fill it to the muzzle with Slip 2000 Carbon Killer
. I let this sit for about two hours. This is way beyond the recommended 5-15 minutes, but I've had it take that long to fully soften old, thick carbon cake on a Garand gas piston, and I'm looking for maximum penetration opportunity here. I did, however, have it etch Parkerizing with that long exposure, so I don't let it get on any kind of gun finish now.
After putting the Carbon Killer into a working solution container (it's reusable), I brush out the bore. This is the only time I use a bore brush nowadays. Newer gun cleaning formulations have become so good, simply dissolving and patching out fouling is all that's needed in a properly conditioned bore. I follow the brushing with the dry patch, Windex, dry patch routine.
Next I put either Boretech Carbon Remover or KG-1 carbon remover in the bore and let it sit 15 minutes. This is followed by the dry/Windex/dry patch routine again. These are thinner liquids than the Slip 2000 product and ensure carbon removal has gotten done in the smallest places. It's an insurance policy, really.
The last thing I do is take an undersize bore brush and wrap a couple of patches around it and smear Iosso Bore Cleaner on the outside of the patches. Iosso Bore Cleaner is a mild abrasive cleaner and you could substitute any other brand you chose. I prefer Iosso Bore Cleaner because it does not seem to contain any petroleum products, and I am avoiding those because of the carbon they leave behind after exposure to firing temperatures in a bore. The bore gets 50 strokes with the Iosso product. The patch comes out black from the polishing action. Again I use the dry/Windex/dry patch routine to remove the Iosso product.
At this point the barrel is ready for break-in or re-break-in, as the case may be. The Howa distributor seems to think it is important to shot the first ten in a clean, cold bore to prevent future heat walking. Whether he's right or wrong, the abbreviated version of the routine that I use is so little trouble to fire, there's no real reason not to use it. It is just 10 shots, and I have modified it as follows:
From the clean bore (if you oiled the bore after polishing, bring some brake cleaner or gun scrubber to the range to get every last trace of hydrocarbons out before firing), fire one shot. Run one wet patch with Eliminator. Let it sit two minutes, repeat. Spray and patch out with Bore Scrubber or brake cleaner to remove any trace of hydrocarbons. That should take long enough to cool the bore pretty well, but if not, wait another five minutes and repeat until 10 shots are down range.
At that point the bore is probably about as well prepared as it is ever going to be short of lapping it by one means or another. Howa has you run 10 more shots, cleaning every other shot, but I don't really see the need. As they say, after shot six you see the improvement, but go ahead and do it if you want to.