Seems like these days the 300 Blackout is "all the rage" as people used to say.

The thing we need to realize about the 300 Blackout is that it was developed to operate on a completely stock AR-15 platform with nothing more than a barrel change. That means the same buffer, buffer spring, bolt carrier group, and magazines. It also has to operate with similar pressure, energy, and momentum levels. If you want to change your .223/5.56 into a lower power .30 cal all you need to do is remove the .223/5.56 barrel and install a 300 Blackout barrel - that's it! BTW, the reason I say lower power is because it is a lower power round than other most 30 cal rounds. Speaking of that…

While it's great that the only difference between an AR-15 223/5.56 and 300 BO is the barrel, there are some consequences that may not be obvious. Prior to the 300 BO, when we've compared the 223/5.56 to .30 cal rounds, the .30 cals have had more bullet weight, more energy, and more momentum, e.g. the 30-30 and .308, etc. The 300 Blackout is not quite up to par with these more powerful rounds. For example, the 30-30 130 gr has 32% more energy and 26% more momentum than the 125 gr 300 BO. And the 300 BO is not even in the same ballpark with the .308.

FWIW, the 300 BO measures .308, not .300 - again for whatever that’s worth, and the same is true for .300 Win Mag for that matter.

Some claim the 300 Blackout was designed to be a competitor to the AK 7.62x39 round so let’s compare the two.

Comparison of 300 BO to 7.62x39 velocity

fps energy

ft-lbs momentum

lb-secRemington 300 BO 125 gr AccuTip 2215 1262 1.23 Remington 300 BO 220 gr OTM 1015 503 0.991 7.62x39 122 gr FMJ 2396 1555 1.30 7.62x39 154 gr Spitzer SP 2104 1516 1.44 7.62x39 123 gr FMJ 2421 1606 1.32

You can draw your own conclusions. For me, the 300 BO is not a ‘peer’ to the 7.62x39.

So why not just use the 7.62x39 instead of a 300 BO? Well, there are a couple of reasons. The design of the 7.62x39 relies on a curved magazine – remember that AK look? So a different magazine would be required in addition to a .30 cal barrel. Because the 7.62x39 is hotter, it may require buffer and buffer spring changes. Seems like I remember reading that the feed ramps may need to be modified as well, but I can't confirm that at the moment.

So why not just up the powder charge of the 300 Blackout to match the 7.62x39? That goes back to one of those not so obvious consequences I alluded to earlier. The 300 BO is designed for the AR-15 platform, hence it must be restricted to comparable pressure, energy, and momentum, and case size of the AR-15.

Not long ago, I bought a Diamondback AR15 in FDE in 300 Blackout. I thought both the 125 gr and 220 gr were real softies to shoot, i.e. very light recoil. Of course an AR is light recoiling but the 300 BO is shooting bullets about twice and four times as heavy as a 62 gr 223 so I anticipated more recoil, but the recoil was noticeably light.

I shot both loads with only foam ear plugs under a tin roofed shooting area and both had muzzle blasts well below what I expected and I was not at all uncomfortable with just the foam plugs. A couple of days later I shot an AR-15 5.56 under a similar roof/range and it was loud enough to me to justify muffs on top of the plugs.

Using Nikon's SpotOn software, I did a comparison of five loads - for simplicity's sake, here are three of them:

Remington..............125 gr 300 BO Hog Hammer

Remington..............220 gr 300 BO OTM

Hornady...................75 gr 223 TAP

Here are the numbers, but it is important to realize that the 300 BO numbers are likely based on a 16" barrel. The Hornady 75 gr .223 is likely based on a longer barrel. This means that the Hornady .223 75 gr will look better from the longer test barrels than from a typical AR-15 16 inch barrel. Soooo….based on a study where they cut the barrel of a 5.56 down in inch increments, I’m going to reduce the velocity of the 75 gr .223 by 150 fps. That’s what the study suggests for a XM855 and I suspect the 150 fps is still a bit high since the .223 is design around 24-26” barrels and the XM855 around a 20” barrel. So keep in mind as you look at the table, the Hornady velocity has been reduced from the SpotOn value of 2790 fps to2640 fpsand SpotOn calculated everything based on that velocity for the Hornady.

Energy (ft-lbs) Load 50 yds 100 yds 150 yds 200 yds Remington 300 BO 125 gr AccuTip 1206 1061 930 813 Remington 300 BO 220 gr OTM 488 474 461 449 Hornady 75 gr 223 tap 1075 991 913 839

Momentum (lb-sec) Load 50 yds 100 yds 150 yds 200 yds Remington 300 BO 125 gr AccuTip 1.056 1.084 1.015 0.949 Remington 300 BO 220 gr OTM 0.976 0.961 0.949 0.936 Hornady 75 gr 223 tap 0.845 0.812 0.779 0.747

Trajectory - zero @ 100 yards - path in inches Load 50 yds 100 yds 150 yds 200 yds Remington 300 BO 125 gr AccuTip 0.26 0.00 -2.54 -7.68 Remington 300 BO 220 gr OTM 3.63 0.00 -12.5 -34.2 Hornady 75 gr 223 tap -0.07 0.00 -1.38 -4.35

So with the 300 BO, we are looking at a 30 cal round designed to be launched from a AR 15 platform, hence it has to be a 'light' .30 cal load. The ballistics have to be limited to that platform's capabilities. Just for comparison of the 125 gr BO to a .223 round, here's a summary of the above table:

at the muzzle...the 300 BO has about 17% more energy

at 50 yards......the 300 BO has about 12% more energy

at 100 yards....the 300 BO has about 7% more energy

at 150 yards....the 300 BO has about 2% more energy

at 200 yards....the Hornady .223 125 gr TAP has about 3% more energy than the 300 BO

Be sure to catch that at 200 yards the Hornady has 3% MORE energy then the 125 gr BO. Although I don't see that energy has a whole lot to do with terminal performance. If anything is going to be indicative of effectiveness I think it's momentum. Next up momentum...

Momentum is probably the least understood, most overlooked and/or ignored, and least talked about of bullet parameters. You rarely find momentum listed in manufacturer's spec sheets, hence it would be easy for one to conclude momentum really isn't that important, but it really is that important.

If it's not bad enough, momentum has to have some weird units - lb-seconds - what's that all about? Well it's a force equivalency expression. E.g. if 1 lb of force is applied against an object for one second, it has 1 lb-sec of momentum. Momentum determines how fast the object the force is applied to will accelerate. An equivalent momentum would be 10 lbs for 0.1 sec. Another equivalent would be a 100 lbs for 0.01 seconds. Another way to understand momentum is the higher the momentum, the more force applied per unit time. It is momentum that provides bone crushing/penetration.

Let me give you an example of energy/momentum performance. Say we go to a bowling alley and try to score a strike with a single .45 ACP shot. Well the round certainly has enough energy, 414 ft-lbs @ 900 fps, which is over 2-1/2 times the energy of a 16 lb bowling ball, 155 ft-lbs @ 25 fps, but the difference in terminal performance is nothing short of incredible! That bowling ball with well less than half the energy can send pins literally flying in all directions whereas the .45 cannot - why? The answer is momentum. A bowling ball has almost 14 times more momentum than the 230 gr .45 ACP, and you can/could see the huge difference in the reaction of the pins. Now that we see how important momentum can be, let's go back and look the momentum of the Hornady 223 75 gr TAP and the Remington 300 BO 125 gr and the 220 gr.

From the Momentum table the momentum

at the muzzle...the 300 BO has 24% more momentum than the 220 gr and 40% more than the 75 gr TAP

at 50 yards:.....the 300 BO has 18% more momentum than the 220 gr and 37% more than the 75 gr TAP

at 100 yards.....the 300 BO has 13% more momentum than the 220 gr and 33% more than the 75 gr TAP

at 150 yards.....the 300 BO has 7% more momentum than the 220 gr and 30% more than the 75 gr TAP

at 200 yards.....the 300 BO has 1% more momentum than the 220 gr and 27% more than the 75 gr TAP

Well it would appear that the 125 gr BO is the clear winner because it has significantly more momentum out to 200yards. However, the 220 gr BO has the same momentum at 200 yards and it can be effectively suppressed. So if suppressed shooting at 200 yards is your game (pun intended) wouldn't the 220 gr be better? Well, no. The drop of the subsonic 220 gr BO is horrible at 200 yards - a whopping 35"!!! That's with a 100 yard zero! I'm not sure all scopes would even let you hold over that much! Plus, even if you could hold over that much, small differences in bullet velocities would result in surprisingly large differences in vertical placement. Simply put, the 220 gr BO is NOT a 200 yard round! Not by a long shot - pardon he pun.

Trajectory of the 125 gr BO is pretty good. The 125 gr BO drops about twice as much as the 75 gr TAP at 200 yards, but the 125 gr drop is a manageable 7.7" and the 75 gr TAP drops about 4.4". So here's a performance trade-off - a flatter trajectory with much less momentum (.223), or more drop (125 gr BO) but with a bunch more momentum. My choice goes to the latter.

The significance of this is depends entirely on the individual and his applications, but the 220 gr 300 BO is intended to be a subsonic bullet. In order to be subsonic, a bullet must remain below 1100 fps. Apparently Remington felt that 1015 fps was as close as they should get. So the muzzle and maximum energy of a 220 gr bullet with a velocity limit of 1015 fps is:

E = .5*M*V^2 = .5* =503 ft-lbs

As you can see, 503 ft-lbs is extremely low energy for a rifle bullet. The Hornady 75 gr TAP has 1161 ft-lbs of energy and the 125 gr 300 BO has 1362 ft-lbs of energy. I.e. the 125 gr has 260% more energy than the 220 gr bullet or stated another way, 2.6 times more energy. Again, I'm not sure how significant energy is in indicating performance.

So why not load the 220 gr hotter? You can’t; it would go supersonic. So we reach a choice, either have a low energy subsonic round or a higher energy supersonic round. Apparently the intent of the 220 gr is to be subsonic for use with suppressors and at ranges not exceeding much over 100 yards.

Subsonic aside, based on the 125 gr momentum, it would appear that the 220 gr BO could be launched from the AR-15 platform at 1258 fps which would result in a muzzle energy of 772 ft-lbs which is better but still low. If pressures were not an issue, and they could be, I think momentum would be the limiting factor for the AR-15 platform. If the momentum goes much higher than the 125 gr, the buffer and buffer spring would be too light and possibly the receiver would not have the strength to handle the increased loading.

Conclusions:

Suppressors and SBRs aside, I believe the 125 gr 300 BO has a significant ballistic advantage over the .223/5.56 rounds. The 75 gr TAP has an advantage in trajectory, but only at long ranges, i.e. 200 yards plus. Out to about 150 yards there’s little difference, but by 200 yds, the 75 gr TAP has dropped 3.7 inches where the 125 gr 300 BO has dropped 7.7 inches. At 250 yards the 75 gr TAP has dropped about 7.8 inches and the 125 gr BO 16 inches.

Drift:

I haven’t said anything about drift up to this point, but I had SpotOn calculate drift for a 5 mph wind from the East – a 90° crosswind. The 75 gr TAP looks better. At100 yards, the 75 gr TAP drifts 0.4 inches; the 125 gr BO 0.77 inches. By150 yardsthe 75 gr TAP has drifted 0.93 and the 125 gr BO 1.8 inches. By200 yardsthe 75 gr TAP has drifted 1.69 inches; the 125 gr BO 3.3 inches. Hence the 125 gr BO drifts about twice as much as the 75 gr TAP.

The drift may seem surprising since we’ve always maintained that a heavier bullet drifts less. However, again, we must remember this is a .30 cal bullet with limited velocity to allow it to be compatible with the AR-15 platform; hence it’s a slow .30 cal bullet so it’s exposed to the crosswind longer than the faster 75 gr TAP. Also, the .30 cal bullet ‘catches’ more wind simply because it has larger diameter and hence more side area than the smaller .223. So it’s quite reasonable that it will drift more.

Accuracy:

I'm still in the learning phase on this. There was an article in a gun magazine where they tested a Wilson Combat AR in 300 BO. It had an 11.5" barrel and they got amazing accuracy from the 125 gr, about 0.5 MOA at 100 yards. The 220 gr at 100 was pretty dismal by comparison and while they didn't say, I suspect the short 11.5" barrel won't stabilize the 220 gr bullet. I've shot my AR 300 BO and see results about the same as an AR in 223/5.56. And that's about all I know about accuracy right now.

Stopping power:

I’m seeing a lot of reports that hunting deer with the AR-15 is getting good results. Jon C. has posted numerous times how effective the .223 has been on hogs. He’s seen this round penetrate the shoulder, which it isn’t supposed to be able to do purportedly, travel through the hog and bust up the opposite shoulder. This is very consistent with other reports I’ve read. It is often claimed that bullet selection is more critical for the smaller .223 round than a .30 caliber round, but remember until the 300 BO appeared, 30 cal not only meant a larger bullet, but more energy and momentum as well. E.g. the 30-30 130 gr has 32% more energy and 26% more momentum than the 125 gr 300 BO. And the 300 BO is not even in the same ballpark with the .308.

My thoughts:

Honestly, I like the concept of the 300 BO. If one believes the .30 cal is a better ‘stopper’, he should keep in mind this is a lower power .30 cal and its stopping power has not been established by long term experience. It seems to me the 125 gr BO has a ballistic advantage over the .223 at all ranges out to 200 yards esp. momentum and the trajectory of the 125 gr BO while not as flat as a .223/5.56, is acceptable. There are three things I see the 300 BO has going for it – it can be fired from an AR-15. It has significantly more momentum than the .223/5.56 round. It has a subsonic round for use with suppressors.

Lastly, if you get an AR in 300 BO, don't be surprised if it won't cycle the 220 gr load. That's a common issue. Purportedly the ARs cycle the 220 gr just fine with a suppressor.

So there ya have it - at least that's my version .