well in short yes, but check this out.
i have a 243 that is a heck of a shooter.
that i bought from mac and i hand fit it to my frame. well stupid me , i use some cheap epoxy to fit the shim to the barrel . well i went out shooting it just the other day and without me knowing the shim had came loose. the barrel (i found out after shooting) would now move while shut from side to side. accuracy went from that nice group, to over a inch and a half pushing two inches. well i put the shim back on (used jb weld this time) and today i shot a group in the .3's and busted every clay at 250 yards and only missed a few at 300, me not the gun.
so heres more proof, the tighter that barrel fits the better it will shoot.