Ammunition Consistency Testing: CMMG, PNW Arms .300 AAC Blackout

Been a while since we did one of these, isn’t it? Thought we gave up or something? Nope, we just ran out of willing victims and needed to re-stock our supplies of voluntarily provided ammunition. I’ve got a couple more to add to the .223 Rem and .308 Win lists, but first I want to start off a whole other category of ammunition being tracked to determine the most consistent brand available: .300 AAC Blackout.

Yup, .300 AAC Blackout — that funky round from the Advanced Armament crew that is slowly becoming a mainstream alternative caliber for the AR-15 platform. With all of the options available (and especially the proliferation of “match” ammo) I thought it would be good to put them to the test and figure out which ones are worth the money.

Speaking of testing, the procedure was laid out in the first one of these we ever published so read up for the technical mumbo jumbo. The only changes are that we have increased our sample size to 20 rounds (from an original 10 round sample) and the test rifle for .300 BLK will be a 16″ upper from Advanced Armament.

First up on the menu is CMMG’s .300 BLK offering. It was one of the first brands to make the ammo available (other than Remington), and it was actually reasonably priced. This is a 147 grain supersonic round that looks to be “military” spec (a little tarnished with sealed and crimped primers) rather than match grade, but is it consistent? Is it reliable in a competition? Inquiring minds need to know.

Next up is a relatively new company whose principles I can really get behind. PNW Arms is all about the science (“Weapons Science” is their tagline) behind ammunition and even provides an entire series of web pages that talks you through the various internal, external and transitional ballistics. Seriously, go read it. It’s worth your time. PNW Arms provided two flavors of ammunition to test (with a third on the way), the first one being a supersonic “match” round which pushes a 155 grain projectile downrange. The cartridges LOOK the part, bright and shiny with smooth edges, but do their polished exteriors mean more consistent loads?

Last on the list for today is PNW Arms’ Defensive loads. Part of the magic of .300 BLK is the ability to use supersonic or subsonic ammunition without having to change anything on the gun, and manufacturers are taking advantage of this by producing both subs and supersonic rounds. These are 220 grain subsonic rounds designed to take full advantage of  a silencer, but alas mine is still in the shop waiting on paperwork.

While I have a minute (and before we get to the results) I wanted to comment on PNW’s box design. It’s simple, lets you know exactly what is inside, and keeps you from accidentally grabbing the supersonic rounds when you really needed the subs. It’s something I don’t think I’ve ever seen in ammunition packaging before and I like it, but that might just be the nerd inside.

And now to the results. As expected, the mean velocities for each box vary inversely to the weight of the bullet. Larger bullets go slower, lighter bullets go faster. It’s all got to do with back pressure and dwell time and such, which I’m sure will make an interesting article sometime soon but not right now. The subsonics are understandably a little “fat” in terms of their boxplot, but the two supersonic “match grade” offerings seem pretty much neck and neck. It’s hard to tell from here, so let’s skip to the interquartile range graph.

And there we have it, a (sort of) clear winner (NOTE: smaller is better for IQR). That IQR difference between CMMG and PNW’s match grade offerings is close enough to be sampling error (2 feet per second), so a rematch might be in order to determine the true king of the hill. Thankfully I have a spare box of PNW M ammo, but CMMG is being stingy on the supplies. We’ll see what the week brings. Oh, and the defensive ammunition has a bit of a spread on it but it’s no worse than the average spread for .308 Winchester and only a little worse than standard .223 Remington. Considering it’s a short range projectile to begin with I don’t see that being an issue.

Stay tuned for more .223 Remington and .308 Winchester ammunition consistency testing results. Science is AWESOME!

And now, the gigantic summary charts.