Can you run whisper ammo through a 300 blackout? What is the major difference between the two? I'm looking for full power BO ammo but am coming up short. If you have a link to that I'd appreciate it as well.

yer good to go. its the opposite case that can be a prob.

+1 What yellowhammer1 posted.

does 300 whisper have any feeding issues in 5.56 mags or are you good to go

Any factory ammo from Hornady or Remington is GTG in 5.56 standard mag. If you reload just keep your rounds to the proper OAL for semi autos and you should have no problem with loading the mags to capacity.

Here is a list of OAL with different bullets that have been tested by the manufacturer to function in a standard AR-15 magazines:  

• Hornady 110 V-Max, OAL: 2.068
• Nosler Ballistic Tip 125 grain, OAL: 2.085
• Remington AccuTip 125 grain, OAL: 2.130
• Sierra 150 FMJ-BT, OAL: 2.080
• Sierra 150 ProHunter, OAL: 2.040
• Sierra 155 #2156 Palma, OAL: 2.130
• Sierra 210 MatchKing, OAL: 2.190
• Sierra 220 MatchKing, OAL: 2.089
• Hornady 225, OAL: 2.140

As stated above you can run whisper ammo through the 300 BLK. It is not recommended to run 300 BLK through the whisper as the chamber dimensions are slightly smaller on the whisper and could cause an unsafe pressure with Blackout ammo.

There is not to much difference between the two cases just that the 300 BLK was designed with cutting down of the .223 case and allowed the chamber to better accommodate the thicker neck that would result from the cutting of the .223 case vs. the whisper which was designed for the necking up of a .221 fireball case and to have a thinner neck. The 300 BLK case will also let you get a little more FPS from you loads vs. the Whisper.

As for the other differences the 300 BLK enjoys a ton of major manufactures making barrels, uppers, rifles and ammo for it. It is SAAMI approved so all of the manufactures can be on the same page when it comes to the specifications of the round. With the Whisper you could not be sure all the different manufacture would have the same dimensions.

As for ammo availability there is plenty out there with more overall and variety coming in the next couple months.

Midway has both subs and supers sonics in stock:

Midway subs

Midway 110gr VMax Supersonic

You can also try CMMG I hear they have some plinking rounds available.