I had the opportunity to test fire my new 300 AAC Blackout upper receiver for my AR-15 last Friday afternoon. Two different loads were tested. One was a 208gr (subsonic, traveling at 1,020 feet per second – per the manufacturer) and the other was a 125gr (supersonic, traveling at 2,325 feet per second – per the manufacturer). My target was an old concrete cinder block.
Recoil and noise was no different than a 5.56 round.
I first shot it with the 208gr round on on the bottom half of the cinder block. There was a nice round entry hole and a little dimple on the back side. I was able to retrieve the lead bullet, copper jacket, and the brass case. There may have been a very small hairline crack on the back but I’m not sure. There was definitely a hairline crack after the follow-up shot. Please note that all photography was done after the testing was complete. The large crack seen in the 208gr exit photo was not a result of the 208gr round. For the 208gr impact, follow the thin shadow line just past where the main shadows start and look real hard to see the 208gr impact. It’s very slight, so you may need to see the photo full size.
Next I shot it with the 125gr round on the top half of the cinder block. A very large entry hole (large enough to easily fit my thumb through the hole) and a good sized exit hole on the back. I was able to retrieve the brass case, but for the life of me I have not yet recovered the bullet. I know that it penetrated both sides of the cinder block. There was a large tree stump directly behind the cinder block, but I have yet to find any markings on the stump from where the bullet may have entered. Numerous large cracks were all over the cinder block.
Pictures of the entry holes are from the same distance and were not affected by resizing. The angle is very slightly different but you can see a roughly rectangular gray rock at about the 4:30 position on the 125gr picture that corresponds to the same roughly rectangular rock at the 12:00 position on the 208gr picture.
A slight motion with my hand was all it took to completely knock the cinder block apart. I did not have to break or use any force to separate any parts of the cinder block.
Recovered brass, copper jacket, and lead bullet from the 208gr shot.