Re: Barrett M82A1
Yes, the M82 should not be considered a precision rifle. It fills a niche for sure, but it's not even close to a 1MOA rifle. I got out of the Army before the M107 was fielded (90s SF we had M82s), so they may have improved accuracy, but it's hard to imagine how you could make the recoiling barrel mechanism any more accurate. With comparable ammo it's almost on par with a Ma Deuce. Still, when employed properly it's a great rifle.
The bolt-action options from Barrett are better, but then there are better bolt action options from other companies as well. After years shooting M82s and some custom .50 bolt guns, experiencing the accuracy of a TAC-50 changed my attitude about .50BMG rifles. These days there are lots of good, accurate options to choose from.
As for .408 Cheytac, the vast majority of extreme range shooters have transitioned to the ballistically superior .375 Cheytac variant. More bullet options and better extreme range performance, hands down. A .375CT is your best option if you want accuracy and distance against paper and steel. If you need to stop a vehicle though, the payload capabilities of .50BMG make it the preferable choice.