What is this groove in the barrel?

[Armybrat]

Grandson wants to buy a co-worker’s S&W AR 15, but was wondering what that cut/groove inside the handguard for.

 

[80sgyrene]

Looks like that was for one of the taper pins holding the fixed front sight/gas block.

However, the low profile gas block looks to be awfully far from that location.

Does he know if the rifle runs reliably?

 

[cololab]

Based on the two photos, it looks like someone has altered the gas block and handguard from what was the factory configuration. Complete photos of the rifle would help. Depending on price and the functioning of the rifle, it may or may not be something worth acquiring.

 

[Yendor357]

I think I’d pass on that one. Hard telling what else is going on.

 

[gwpercle]

Looks like it's been "monkeyed" with ... Buyer Beware !
At the very least ... shoot it before you buy it .
Gary

 

[bamashooter]

Ask the seller.