I have an old oringal JDJones Super 14" .300 Whisper barrel for my Contender and had it for years I have killed lots of groundhogs and Crows, and my share old Whitetails with it. I prefer the 125gr Nosler BT it is good as it gets, I just started trying the factory Hornady 110 Vmax and they good.

A friend of mine just bought a 300 Whisper barrel and said he has been shooting the .300 Blackout ammo in it. I told him that it is different like Gary said the shoulder is slightly forward! He reply "Nope"... Ok , I know myself that it is different! -Right! So I called SSK Industries and talked to JD. ...and he said your right they are different... but you can shoot the .300 blackout in a 300 Whisper barrel, but he wouldn't recommend it in a AR platform because of feeding issues.
I respect JD a lot but I'm still gonna shoot .300 Whisper ammo in my barrel.