Ever since it's introduction there have been heated debates into the wee hours of the night about JB Bore Paste, pitting man and beast against each other about it's miraculous cures for severely fouled bores and how others were ready for the scrap yard by merely opening the jar near any barrel in the house. Well Ladies and Gent's it is time to dispel all the myths surrounding this diminutive ivory jar, that has carried many of us benchrest shooters over the threshold into the "Benchrest Hall of Fame".
Before we get into the "PROPER" use of JB Bore Paste lets dissect the process that takes place within the bores of our firearms that cause the degradation to their inherent accuracy.
Upon firing a round down our barrel the greatest culprit is heat. In many modern cartridges the bore temperature reaches or exceeds the melting point of steel for a micro second. This is the reason for the large diameter barrels one typically sees on many firearms built for competition, the greater mass of steel serves as a heat sink to draw the heat away from the bore in a the most expedient manner. Second to heat is pressure. With every round that passes through the bore pressures can rise to nearly 75,000 PSI causing the bore to expand and contract, possibly thousands of times over its lifetime.
These first two mechanical processes are what set the stage up in the bore for all fouling that with begin to manifest itself after microscopic fissures begin to form from the heating and cooling and expansion and contraction that take place with every shot. Remember heat, pressure, & carbon is what forms diamonds and the carbon fouling is about that tough to get out.
The last culprits in our un-holy trinity that lead to fouling our bores are machining defects in the bores themselves. These can be reamer marks left from a poorly chambered barrel leaving the free bore and throat scored and rough, too tight a pilot on a reamer can also severely scratch the tops of the rifling for an inch or so in front of the throat. Tool marks left in the bore from the rifling process also play a role in contributing to fouling and rapid accuracy drop off.
Well just when you thought there is no way things could get worse, HANG ON, THEY DO!!!!
Let's throw all of these nasty things in our blender along with a bit of carbon from the burned powder and primer residue and gilding metal from the jackets of our bullets and maybe even a pinch of lead and plastic to complete our ballistic cock-tail. Yep! Time to re-barrel after the mess we just made....RIGHT!!!!
Wrong! Bwanna, this is where our old buddy JB steps in at the last minute and saves the day, gets the girl and rides off into the setting sun.
That would be great if it were that easy but I am going to continue with our saga just a bit longer, so grab a beer or a whiskey if you need one by now and read on.
The heat & pressure generated in the process of firing that projectile down the barrel begin to fuse the carbon to the metal of the bore, to a greater or lesser degree according to the condition of the bore, then as the projectile passes over this layer of carbon it leaves behind a small copper wash, with each shot this laminating process continues to build until we have a marked decline in the firearms performance. Now, what the typical shooter can see is the copper wash left in the bore after a string or shooting session. This copper fouling is easily addressed by most solvents on the market today, but they only address the copper and whatever loose carbon residue lies in the bore. Under close observation with the Hawkeye bore scopes sold by Brownells it becomes very apparent that only the copper was removed in the cleaning process and that the underlying carbon was not touched at all and is ready to begin its fouling process with the first round passing through this now supposedly clean barrel. With the bore scope one can easily see all of the remaining carbon in the bore. These are noticeably darker streaks in the bore as compared to the surrounding metal. I always recommend the purchase of a bore scope, it is the only way to accurately judge the condition of ones barrels. If you can not afford one individually get together with your shooting buddies and purchase it as "Group Insurance". Sorry couldn't resist that one.
OK, we have finally got to the good part. Finish your drink; roll up your sleeves, because we are going in.
The "PROPER" use of JB Bore Paste 101:
Most methods of cleaning with JB Bore Paste such as a patch over a jag or a patch over a brush address the tops of the rifling and the center of the grooves but leave the area where the groove meets the rifling untouched as observed through a bore scope (Yours is probably on the way by now!). So, how do we get around or overcome this perplexing predicament? I have made you wait long enough so here we go........................................................................................................
Here is a pretty picture of a rifling button. As one can see it has the reverse imprints of the rifling helix ground into it, but most important is its shape. If you look closely it resembles a football with its ends lobbed off, as the rifling button passes through the reamed hole of a barrel blank it completely fills the bore swaging the impression of the rifling as it's pulled or pushed through the barrel. In essence this is what we're going to attempt to accomplish. We want to mimic the rifling button in order to fill 360 degrees of the bore and groove of our barrel in order not to leave a single spot where carbon fouling can hide.