Just a different cutout design just like in the other specialty steel barrels.

 

Example

https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/293017260573

https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/123703599219

https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/293018716248

https://rover.ebay.com/rover/0/0/0?mpre=https://www.ebay.com/ulk/itm/123701050366

 

You mentioned SuperGrade--SuperGrade barrels are for the "quick-release" type of KIDD receivers and not the slip-fit.

 

AND..

Our Fluted Lightweight 556/762 .22LR barrel : This lightweight bull barrel design is unique due to the singular construction of the barrel, breech to muzzle. Then we sleeve the barrel with a black or silver anodized tube to give it a bull barrel look, along with an extremely rigid and durable construction. This innovation in the .22 barrel gives it unparalleled accuracy in this weight class, guaranteed accuracy of 1/2" at 50 yards. As an aside, if you are looking for an even lighter lightweight .22 barrel, we offer the Ultra Lightweight barrel.

The Kidd 22 Fluted Lightweight 556/762 barrel has a bull diameter for the first two inches and then steps down to .870 until the muzzle. The bull barrel channel of .920 barrel channel works perfect for this barrel. The 18" barrel weighs 2 pounds and the 16.5" barrel weighs 1 pound 14 ounces.

The Match barrels are .920 and do not step down.. heavier.

I personally have a bunch of each.. I do not see much if any accuracy difference and for a combo Bench/Packer I much prefer the Lt. Wt.'s.
For a dedicated Bench rifle the Match barrels are IMO unbeatable.

As stated above the Supergrade barrels are NOT for the slip fit receivers... watch this Vid...

 

Super accurate.. Super cool...

 

Thanks

Thanks for all the info. I'm ordering a Supergrade rifle. I have several mixed up builds but I would like to have a 100% Kidd.