Quote:
Originally Posted by 260 Rem
Kreiger says that bore BI is not necessary in lapped bores but when the chamber is cut, reamer marks are left in the throat which lay across the direction of bullet travel. Until these “marks” are ironed out they pick up copper from the bullet jacket which is vaporized and deposited in the bore just forward of the chamber. Since copper adheres to copper very well, a build-up can occur which becomes difficult to remove later. Hence, Kreiger recommends a shoot-and-clean cycle to BI their barrels.
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True, I have a shortcut I use in Factory barrels where I use a jag with 2 or 3 patches that will not fit down the bore but will fit in the throat far enough to reach those rotational reamer marks at the beginning of the lands. I saturate the patches with red JB paste, using a boreguide that keeps the rod and jag centered, insert the cleaning rod and gently bump the leade with the jag and enough patches to allow it to squeeze into the throat yet no go into the bore and gently bump the throat 50, a hundred or more checking with the borescope as I go and smooth the cutting edge off the sharper tooling marks on the throat of the lands. I like to describe this area (for lack of a better word) the 'land ramps'. I wouldn't do this with a quality barrel but sometimes factory barrels can be pretty rough, it can't make them worse, saves running precious bullets and powder down the bore trying to as some call it "iron out" those tooling marks.
Personally in my opinion it is not the bullet travelling over these marks outside of the first 1 or 3 shots where the actual soft bullet jacket may trap and collect any microscopic loose edges of these machining tool marks as they passes over the throat that smooths these marks but rather the blow torch effect of powder combustion and extreme temperature that eventually causes the firecracking that we are all familiar with that rounds off those copper stripping sharp edges. Just my current thoughts, subject to change and enlightenment.
