Carbon buildup ???

[Preacher]

I sure do love this site and for a old groundhog shooter I have learned a lot by listening and looking, hopefully it will all come together when I get my 6br finished up.

I was shooting my new 10 twist 6mm Ackley using 80 grain Fowlers over 45.0 of H4350 at 300 yards very well again the other day when the last 6 over the 35 Oehler showed the velocity climbing after each shot. they had been all at a 3410 average until these last 6. I had been shooting three at a time at a target, and had about 40 rounds out of a clean barrel when this happened.

#1-3448-fps
#2-3455-fps
#3-3467-fps
#4-3476-fps
#5-3499-fps
#6-3519-fps

This has never happened before, I was wondering about that but had no clue as to what was going on, and now I see that Jason mentioned this in a article, and I'm wondering if this is what happened ?
Was it a carbon build up problem ?????

JB said ----,, 1 patch of JB paste scrubbed in the throat and full length ~10 times knocked out the carbon and dropped the velocities back where they should be.))

 

[jb1000br]

Was the barrel hot?

How long were the rounds chambered before you shot them?


RE: carbon

In my situation,s) the carbon resulted in a gradual climb in average velocities,over ~100rds or so) spreads WITHIN chrono'd groups were still VERY tight, but the average seemed to climb...

when the average climbed out of my happy spot, vertical appeared.

JB

 

[Preacher]

Not hot to speak of but maybe a little warm. It's a #7 taper Pac-Nor and I have no reason to run it hot to the touch.
My bench is in the partial shade and it was in the real high 80's by the end of the session. it's been like that for the past few times I've shot.
I shoot em as fast as I get em in the chamber, but I do let it cool before shooting again.
That particular day I was shooting the same three cases over and over, and then back to the shop to reload them again, so the barrel was not hot at all during the day.
Maybe it was just one of those things that make you think.....

 

[chino1969]

Preacher,
Interesting observation on the velocity climb. H4350 is an Extreme powder which is fairly temperature tolerant, so I don't think the temperature of 80 degrees should have given you a pressure increase the way H380 would, for example. I would probably try the same load and see if it re-occurs and go from there. Little things like that can drive you crazy, if you let them. The bottom line is how are your groups downrange? If they are little bugholes, I'd leave well enough alone. If you see the effect of this on your target, then investigate further. Let us know what you find.
Regards,
Chino69

 

[tenring]

Several years ago, a very well known IBS competitor told me how to eliminate the carbon ring which forms just ahead of the case mouth. Find an old arrow, remove the field tip, insert a brass cleaning brush one caliber small, twist a patch around it, and load the patch with JB, Iosso or other favorite. Chuck the other end of the arrow in a variable speed drill, and turn it while brush is inserted into the leade. The number of passes to remove the carbon ring, can only be determined by examination with a bore scope.

 

[BountyHunter]

take the same arrow, put a file handle on it and put a 45 cal plastic bore brush in the screw in insert.

wrap with shotgun patch and makes great chamber cleaning tool and cleaning rails when done.

you can also make any length you want and not have to fight with little 10" tools and trying to get under the scope.

I have a set with 20" and work great.

BH