It actually a red apple to green apple comparision . Reason being is the SR15 is has "hard use" hammer forged barrel ( made by Diemaco / Colt Canada ) chrome lined
The Noveske Afgan has the Pac Nor blank button rifled at Pac Nor with Noveske proprietry tooling . Barrel is hand lapped
As already mentioned these stainless barrels are stupidly accurate . I have used the SPR lengths in both 5.56 and 6.8 SPC , 10.5s ( who ever says 10.5s can't be accurate is full of crap ! ) , and 14.5 length. All are great shooters
The better comparision to a SR15 is the Noveske N4 ( blank made from M249 machine gun barrle by FN ) that has chrome lining twice as thick as standard M4
I did a comparision a while back and here are some pics ( both are 16" but you get the idea ). The uppers were about the same price range
As you can see the bolt ( radiused lugs setc ) , camp pin ( smaller dia ) have been redesigned to minimize stress risers. It is readily apparent that there is more meat around the cam pin hole in the E3 bolt. Notice goofy firing pin to fit in smaller cam pin
Both uppers were of similar accuracy .
Having said that, in my experience, neither shoots match ammos such as 75Gr A-Max , 77 SMK , 69 SMK as well as the stainless Noveske barrels
No one buys these uppers to shoot tiny holes on a bench
Both these hammer forged barrels have freaky light proflile compared to the Noveske stainless profiles
Bottom line , I highly doubt you will shoot out the Afgan barrel any time soon, but if you think you are want to put 20K rounds through a barrel before you replace it then your choice is the KAC SR15 or Noveske N4
I don't "need" a hard use upper like the SR15 / N4 . If I where to have only one upper in 5.56 I would prefer Noveske Stainless barrel
BTW - a USGI bolt will function ( and headspace properly ) in place of KAC E3 bolt "for emergency purposes" according to KAC