I've got a precision AR that will turn in .7 moa five-shot groups (usually at 200 yards) when things are going well. I haven't been shooting measured groups with it lately, but I suspected that accuracy was degrading. A few days ago, I shot a couple of measured seven-shot groups (200 yards) with loads proven to be capable of under 1 moa in this rifle. Both groups measured about 2 moa.

The rifle has maybe 1,000 rounds through it. I don't clean thoroughly often. After every trip, some CLP goes down the bore and one patch goes through the bore. I remove carbon fouling every 300 rounds or so. I gave the rifle its first copper fouling cleaning after that range trip. The bore was dirty and a good bit of copper came out, but not a crazy amount.

Can a dirty, fouled bore add 1 moa or more to a group?

Surprised a lot of folks aren't jumping in on this thread. Perhaps you should cross post it to the technical forum since this is more of a technical question on precision/accuracy in relation to cleaning habits.

Generally speaking, you should be getting better groups when the barrel is dirty. Chances are your ammo selection is the cause of this.

Seems like a good cleaning especially the bore and chamber would be in order then retest it.

Depends on the barrel and ammo.

Before my last range trip, I thought I needed to clean my barrel (250 rounds fired, 69gr fgmm).  Well, ran out of time and went shooting without cleaning.  I put 60 more rounds downrange and it grouped fine.

I suspect I'll need to clean it before the next outing.  

I'm shooting a shilen barrel.  It was easy to clean when I got it and has only gotten easier.  I'll probably brush and patch the barrel with Hoppes to remove carbon and powder.  I quit using copper solvent after the first 5-600 rounds.

Many shooters are moving towards a "clean when accuracy falls off" standard.  Benchrest shooters clean after 20rds.

When I started shooting a .22 league I found that I was doing great until I cleaned the barrel thoroughly. That day after cleaning the barrel my score sucked and just could not figure it out. After talking with a couple of the older guys I discovered my cleaning had indeed changed things up. After some more random shooting my scores settled back in. So to me clean when you see a drop in accuracy

Yes, how much who knows, do you have a muzzle device?  They can accumulate a lot of carbon around the crown that goes unnoticed.

1000 rounds is getting up there, I  go 700-900.....to clean the barrel of copper, chamber maintenance gets done much more often.