My small frame 'long range' wildcat most you can squeeze into AR15magazine and onto a 7.62x39 bolt face.

6 SPARC compared to  6BR 

6 SPARC chamber green , Hornady 6ARC blue

Hello Mr.T, what is the concept behind this wildcat, and what advantages does SPARC offer over ARC, thanks 

More speed with great ES&SD , something that would squeeze max from my bolt action rifle design that feeds from AR15 mags

In the competitive world, 6ARC turned out to be a bit of a dud , to small to push the 105grain bullets at decent speeds.

That was well understood before ARC even existed when 6AR  came to the scene and 6ARC is nearest clone. 6AR spawned wildcats with more case capacity in the form of 6ARturbo,6ARTurbo40 ,6FatRat  my wildcat is close the these with shoulders blown forward and 40° shoulder angle plus non tapered case .

https://www.6mmbr.com/gunweek068.html

6AR and 6ARTurbo40 

Note there are cartridges with more case volume for AR15 ,like 6HAGAR build on base of .30Rem but this is how they are loaded for feeding from the magazine