Many barrels shoot better when a little dirty...Going to the range or field with a pristine clean barrel is asking for a variation in groupings...
For hunting purposes where the first shot is possibly all you will get, leave your rifle slightly fouled when you put it away and you will pretty well be able to know where that first shot is going...It won't hurt the barrel unless you are going to leave it sit for six months in the safe...
New ARs in particular don't seem to shoot really good until you've run 100-200 rounds through them as a 'break in' anyway...Whenever I've got my hands on a new one, I'll run a hundred rounds of the cheapest military FMJ through it, just to burnish the bore, before I start building hand loads for it...
If I'm shooting for groups, I'll run through 8-10 rounds before I ever consider expecting tight little groups..then, if I get a 'flier', it's usually because I realized that I a good group forming after 3-4 shots and broke my concentration by thinking about how good it was looking, rather than concentrating on how I was holding the weapon, my sight picture, or my breathing control. or my trigger squeeze...It's more a mental thing than anything else...