I had a .22-250 that would throw soft-ball sized groups at 100 yards if I gave it a good cleaning. It would take about 10 rounds before the groups would shrink to 1/2 inch.
So I would just run a bore snake through it once after every shooting session. I put about 5,000 rounds through that rifle then had it re-barreled.
Keeping the barrel fouled 99% of the time sounds counter to everything we learned about cleaning guns but I know what I experienced.
I'm not saying this is the case but maybe you might try running box of the cheaper fodder through it. Then see how it groups.
I've also noticed that the type of bipod or rest that I'm using makes a difference. I hate shooting off benches. This is especially true with concrete benches. The rifle bounces too much under recoil. I would rather shoot prone with my bipod in the dirt. My accuracy is better that way.
I really like the atlas bipods with the legs at 45 degrees. If I have to shoot off the bench, I've learned a trick to emulate some of the "give" that a dirt surface has under recoil.
Place a section of stiff foam padding with a carpet section on top of the bench. I have 1" foam padding for exercising on that goes under the carpet section. Then rest the bipod feet on the padding.
This has just enough give and lessens a lot of the bounce that concrete benches produce.
My apologies if it sounds like I'm insulting your intelligence because it seems like you know what you are doing but just want to help.
This is my Savage Impulse in a Boyd's stock and a group it produced. By the way, this thing hates bipods. It will only take a Harris or Magpul but with them the croups approached your 6 inch results.
I now shoot it prone, resting on the bags with my support hand under the fore-end pulled tight against my shoulder.
Before I did that, I tried everything and the groups were really large. So out of desperation, I pulled off the bipod and held it like I did my WW2 sniper rifles and Winchester M70 Bull gun, which don't take bipods. I really love this rifle now.
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