I did two articles on Ruger firearms. One was on their Mini-14 in .300 Blackout [1], and the other was on the new Ruger SR-556 [2] Take Down rifle that comes in .223/5/56. In the latter, you can swap out the barrel and convert it to fire .300 Blackout/.300 Whisper ammo, which is a neat idea.
I didn’t shoot any heavy, sub-sonic .300 Whisper ammo that Black Hills Ammunition [3] produces, because this ammo is meant for use in guns with a suppressor on them. This isn’t the first time that Jeff Hoffman, at Black Hills Ammunition, asked me to do some testing for him on some ammo. Jeff sent me some of his .300 Whisper ammo to test in both of these rifles. Included was his heavy 220-gr OTM sub-sonic ammo, to see if it would function in either of the above guns.
The Ruger Mini-14 in .300 Blackout did actually function with the Black Hills 220-gr sub-sonic ammo Jeff sent me. However, the empty brass was just barely getting out of the chamber, and the empties only fell a few feet from the gun. Still, the Mini functioned 100% of the time for me with the heavier sub-sonic ammo. This isn’t to say that another batch of the same ammo will function with it; ammo varies from batch-to-batch, so keep this in mind!
Next up was the Ruger SR-556 Take Down, with the .300 Blackout barrel installed, again using the .300 Whisper 220-gr sub-sonic ammo provided to me by Black Hills. I adjusted the gas piston up and down from fully open to fully closed during my testing, and the heavier ammo would sometimes function with the gas piston fully opened. However, the empty brass was just barely dribbling out of the ejection port. Most of the time, the gun wouldn’t function with the sub-sonic ammo from Black Hills. The empty brass would either just stay in the chamber, or those that were pulled from the chamber wouldn’t eject, tying the gun up.
Now, keep in mind that this was very limited testing with the two guns I had on hand. I wasn’t totally surprised that the Mini-14 in .300 Blackout functioned. They allow a lot of gases to push that fixed piston back, but the gun did function. However, it may not function with another brand of sub-sonic .300 Blackout/.300 Whisper ammo. I was hoping that the SR-566 Take Down would function, but it just didn’t most of the time. Again, this is only one gun sample. Others might do better or even worse. For the most part, the SR-556 in .300 Blackout was a jam-a-matic. Of course, this was no surprise. The gun is designed to operate with the heavier .300 Blackout/.300 Whisper ammo with a suppressor installed on it. The failures were not the fault of the gun and/or the ammo. It was just a test to see if the gun/ammo combination would work.
So, if you have a Ruger Mini-14 in .300 Blackout or a Ruger SR-556 in .300 Blackout and you’ve tried to fire them with the heavier sub-sonic ammo from Black Hills Ammunition and your guns didn’t function, don’t blame the gun and the ammo. They are meant to work in suppressed rifles. If you have another brand of AR-15 that is chambered in .300 Blackout, you might want to try some of the heavier Black Hills .300 Whisper ammo to see if it will function in your rifle, without a suppressor attached. Ya’ never know.