Chigurh has a total of three weapons - a captive bolt, compressed air stun gun; a Marlin Camp Gun (.45 ACP semi-auto) with suppressor; a semi-auto 12guage shotgun - also with a supressor. Chigurh drops the 45 Marlin Camp Gun which Llewelyn picks up. He then reverts to the suppressed 12 guage shotgun.

The two suppressed weapons are similar in appearance. But there is no error by the film maker here.

Right after Llewelyn jumps to the ground (after Chigurh pops in invited) and runs to the truck, the driver is shot and then Llewelyn hides. After Llewelyn shoots at Chigurh Llewelyn picks up Chigurh gun and stands there with both guns. Jump to the next couple of scenes and Harrison is confronted by Chigurh on the stairs with none other than the lost gun. Where did Chigurh get the gun if Llewelyn took it. I think it is a major blooper and not a nitpick