Well I finally ran into some problems with the original "dirty" 6BR. For those that haven't been following along, this rifle has been one of two rifles which were the basis of an experiment I have been running on the behavior of barrels which are not cleaned. Load workups were done after 250-300 rounds had been fired on each, to get the bore heavily fouled and then get a very tuned node established... and then see how long it takes to come out of it.
I had 1530 rounds since it was last cleaned, and it pressured up bad, and quick. The barrel has just over 2500 rounds total now. I had 100 rounds loaded up all in the same batch, and pressure started about 30 rounds into it, so it presented a nice opportunity. In the name of science, I sacrificed a few pieces of brass to the cause. Once it pressured, I tried some things to make double sure it was the bore condition that was causing it and not some other variable. I had been able to run the same loads during the entire "fouled" condition of this barrel, so after about 300rnds to foul in, my loads have not needed to change across multiple bullet types.
When I say it started to pressure, I mean it was violently demolishing brass. From the onset of pressure on the left, to where it ended up when I stopped on the right. The things I do in the name of science... :rolleyes:
The following was done, with no positive effect:
Removed the suppressor.
Cleaned the chamber.
Cleaned the brake.
Seated bullets deeper 5 thousandths (making sure no cold weld)
Full inspection of bolt, trigger, and action components.
Pushed a dry patch down the barrel.
Rounds were fired after each step to check each variable independently. No change was observed, as pressure signs on the brass were equally high at each step. Final step was to clean the bore!
When it first started pressuring up, I put it on paper at 100yds and fired two 5-shot groups. The top group was first, then it started hitting pressure bad, and the second group is on the bottom. Obviously went fully haywire.
Here's a short video showing the bore condition at the time of cleaning, with roughly 1564 rounds since the previous cleaning.
I went at the barrel with wipe-out patch-out and accelerator, and after a few cycles with heavy brushing... I went to Flitz polish and used some aggressive pellets and viciously polished the bore. I could have kept at that for an hour and still not got it all the way clean I think.
Here's a video of where I ended up.
After cleaning I fired 5 rounds on steel, just to settle it in a bit. Then I fired a couple 5 shot groups at 100yds. First one was a bit wild... as I suspect the bore wasn't quite settled in yet. Second one started to look much better.
While I understand none of this will be a huge revelation... its still nice to have some quantifiable and observable results with a rifle that has had a good barrel log. The same load that has always run well in this rifle, ran well after I cleaned it up. At 2500rnds, the barrel is still performing acceptably. It's also noteworthy that the rifle went right back to its previous zero once cleaned. The remaining 20 rounds which were fired after cleaning, exhibited no adverse pressure. This Benchmark barrel has certainly exhibited some excellent stability. It will be interesting to see how it behaves going forward.