Barrel diameter issues

[Slyver1983]

I have a custom barrel for my bushmaster 18" 1:16 5r. I have been having erratic groups with copper bullets in .451 diameter for the last three years. I only shoot coppers on a clean barrel (bare metal). I recently slugged the barrel and it has a .4500 diameter till about 3" from the muzzle then it goes out to .4507- .4508 on my starret mic depending who reads it. My question is will this cause the inconsistency I have been seeing in my groups. 1" groups then 3" groups back to back everything else has been checked.

[Al in Mi]

what's it do with other bullets?

[Texas Sheepdawg]

How does it shoot with .452 diameter bullets or factory Hornady 250gr FTX?