MP-15 .22LR Question - Groove in the bore?

[.444 Marlin]

Kinda hard to see since its a cell phone pic but this groove that goes completely around the bore is about 3 1/2" from the muzzle. It doesn't seem to be hurting accuracy much if any because 25yd groups are about 1-1 1/2" and yesterday I popped several squirrels from 50+yd with iron sights.

Can anyone explain what this is and/or why its there?

 

[.444 Marlin]

The rifleling continues on both sides and into the groove.

 

[Tiny]

Mine comes to the crown and I can't see a ring.Mine is the Tactical version with flash supressor.

 

[TiminTN]

That needs to go back to S&W. I`d call it tooling marks from something that used a mandrel inside the barrel.

 

[mr.big]

1 inch groups at 25 yards needs to go back irregardess

 

[DaveTN]

1 inch groups at 25 yards needs to go back irregardess

I�m confused. You think a .22 shooting 1 inch groups at 25 yards with open iron sights needs to go back to the factory?

 

[mr.big]

1 inch groups at 25 yards needs to go back irregardess

I�m confused. You think a .22 shooting 1 inch groups at 25 yards with open iron sights needs to go back to the factory?

if that is the best it can do with its fav ammo,,I aint got any use for it.

 

[mr.big]

is the bbl long enough to chop it off behind the groove