Nothing seems to work like …

Since I wrote this post, I’ve come across several articles on cleaning bores with JB. Frank Green of Bartlein Barrels posted some photos of a bore that was apparently deeply grooved by cleaning it with a bronze brush and JB applied to a patch wrapped around the brush. The lands looked pretty bad. Perhaps a steel brush was used? 

I’ve used this cleaning method for some time now on multiple rifle barrels to no ill effect, but I want to pass this new information on. I suspect the key is the use of a worn bronze brush to minimize the pressure the bristles put on the lands. And don’t brush more than necessary, 5 to 10 strokes then check the bore. 

My advice is to use a borescope to watch progress and don’t get overly aggressive with it. Watch for any signs of scratching/grooves on the lands.  I clean with JB about every 500 rounds. 

Next time I clean the bore with JB on my Service Rifle, I’m going to try a tight fitting patch on a PH style jag and borescope to see how effective it is. This is the method that Frank recommends. 

There is a lot of controversy in using brushes (even nylon) in rifle bores from barrel makers. Some say never do it. Some say it can’t harm the barrel, even a bronze brush. But perhaps JB and aggressively scrubbed with a bronze brush could cause this damage. 

I've heard stories of people attaching an electric drill to a section of cleaning rod with brush attached to try and get the carbon out!  That would not end well.  

I had just finished cleaning both my AR's with JB on patch wrapped around the worn bronze brush, so won't need to clean again with JB for several months.  I've shot the AR twice since then, and it still hammers.  Its soaking right now with Hoppes 9 in the bore (my routine cleaning method), once I dry that out I plan to go borescope it again and look very closely for any signs of scratching/grooves on the lands.  I'll also check the bore with pin gages and measure throat length.  This barrel has been cleaned with JB with bronze brush/patch at least 5 times now.  

This! 

Although I found the VFG adapter a bit of a fiddle with the small nut; the Brownells adapter on the other hand is slightly thicker and I believe it did a better job giving slightly more friction on the bore. 

I think there would be less chance of rounding the corners of the rifling by using a PH type jag vs a brush. What I liked about the bronze brush is it cleaned the grooves too, and all the carbon trapped into the corners of the grooves.

Chrome is harder than normal barrel steel, so should not be as susceptible to wear. 

I measured the bore on my AR Service Rifle and could not detect any wear. 0.2180+ pin gage just fit with no play. 

After reading Frank Green’s (from Bartlein Barrels) article on cleaning the bore with JB on a patch wrapped around a bronze brush causing severe damage in the form of deep grooves/scratches, I decided to back off cleaning with JB for a while.  Looking thru the log book, I found that it had been over 1000 rounds since I last cleaned the carbon out of the Bartlein barrel on my AR Service Rifle.

Following the November Talladega 600 Matches, I thought it was time for a deep cleaning on the AR. I had only done what I call “routine cleaning” after every shoot over the past 1000 rounds (6 months of shooting this rifle).  That is patching out the bore with Hoppes 9, let it soak 12 hours, then wipe again with Hoppes 9 and repeat for a few days.  This time, I followed Frank’s recommendation to use a PH style jag with JB on a patch. I use an 1.5x3 inch patched wrapped around the jag. About 20 strokes in the throat and first 8 inches of bore forward of the chamber. That removed about 90% of the dark hard carbon based on borescope images.  

I did this cleaning the week before the final EIC Service Rifle Match of the year that I’ve recently posted on. But, I knew enough to “never come to a match with a clean barrel”.  Now, that doesn’t mean show up with a fouled barrel either. It means don’t show up with a squeaky clean bore from using JB when you haven’t used it for six months and 1000 rounds!  Now I know why…

So, I took the rifle to the Talladega range last Friday, the day before the match, to make sure I had solid zero’s for the EIC Match (which allows NO SIGHTERS). To my surprise, the zero’s were off, by 1 MOA at short range and 2 MOA at 600 yds.  The muzzle velocities were also lower, by 80 fps for my 600 yard load. I would not have won that match on Saturday if I had not found this out on Friday. 

So what happened? 

At first, I thought it was the cold weather, it was 34 deg F that morning.  But N135 and N140 is supposed to be quite temp stable.  It then occurred to me it must have been hard carbon building up in the throat and first few inches of rifling that was providing a tighter gas seal around the bullet. The result was a gradual increase in muzzle velocity over time that was not detected. This theory explains why my elevation settings had been gradually coming down over the last 6 months, I had to reset the elevation turret a few times back to “0” index at 200 yards.  Then with the carbon cleaned out, the muzzle velocities dropped and elevation settings had to go back up to compensate. 

We don’t normally get more velocity without also increasing pressure, but I doubt an 80 fps increase in velocity is creating dangerous chamber pressures unless the load was at max to begin with, and that was not the case.

So, I’m now going back to cleaning the throat with JB about every 300-400 rounds, and watch for any change in 600 yard elevation zero. But, it will be on a patch wrapped around a Parker Hale jag (at 90 degrees to the jag, not diagonally and not on a bronze brush. 

At the other extreme are the bench rest shooters who clean after every round with bronze brushes.  And they junk a barrel after a few hundred rounds max (no wonder).   All depends on what level of accuracy and repeatability you are looking for.  

With great difficulty using that method!