Cleaning and accuracy

I've got a Remington 700 with a 24" Lilja 1:8" twist, 3-groove, chambered in 260 Remington.

It's probably got about 2000rds through it. I haven't really kept track. Looking at the throat with a bore-scope, I can see it's been cooked but it isn't THAT bad.

The last couple of matches, it seems like my accuracy disappears as soon as the buzzer goes off.

For example, I ran down to PWSA on Thursday night. Rifle wasn't "squeaky clean", but didn't have that many rounds through it since it was last cleaned. Got a good zero and everything was great. Fired maybe 80rds in ~2hrs.

Cleaned up the barrel really, really well on Saturday night. Scrubbed out a lot of powder.

On Sunday -- first shooter, first stage -- I couldn't seem to hit anything past 200yds! Buzzed through 50+ rounds before the buzzer went off @ 8 minutes.

2nd stage was better, but mostly because the targets were closers. Still couldn't seem to hit anything well beyond 200yds.

Did fine. Actually did great (for me) on the 3rd stage slow-fire with all 200yd targets.

So my question is how much affect (positive / negative) would you expect cleaning to have on your zero and general accuracy?

My other theory is maybe something is happening when the barrel gets really hot that's throwing off my accuracy. Since the rifling is worn-down anyway, maybe the expanding barrel brings the rifling out of contact with the bullet jacket?

Mike