Choke shows "scouring" on one side

[fiorgobas]

Friend asked me about this, mossberg 20GA pump with chokes in place they show scouring on one side of the choke. Looked at chokes, they are round and uniform in wall thickness, barrel with no chokes does not show any scouring on one side. Tried different factory ammo no change.
Ideas??

 

[StoneHorse]

Chokes just a little rough on one side, stripping off a little more of the plastic wad? Try a aftermarket choke and see if problem goes away.

 

[stubblejumper]

If this happens with multiple chokes, it's possible that the barrel is not bored and threaded square for the chokes.

 

[Longwalker]

Shoot the shotgun on a pattern board. Several shots, not just one. pattern results will tell you if its a problem or not.

 

[rembolt]

Are the chokes actually scoured or do they have burnished in wad residue ? how much and what size steel shot has gone through the gun ?