Good or Garbage in SBRs? 77gr OTM 5.56 from Black Hills

Well first up, it’s not garbage. This is some really neat stuff. I just needed a clickbait title for the search engines. What I’m trying to do is find out is if this ammo is good for what the internet says it it’s good for: basically everything. I have a sneaking suspicion that it’s not. Also, this ammo was provided to the blog by Ammo To Go. This literally would not have happened without their contribution, so go show them your thanks.

Background

What is the ammo we’re looking at? It’s a 77 grain open-tipped match bullet designed for precision work originally asked for by the US Navy [sauce]. Now if you read online, some people will talk about how this round is great in SBRs because of it’s high grain weight and open-tip construction which makes sense if you only sort of understand how ballistics works.

Since 5.56/.223 is a velocity-dependent round, the energy downrange is mostly determined by the bullet’s velocity [read more here]. But velocity is dependent on barrel length, and short barrels are in vogue these days. So what it do? If we can’t get more speed, can we get more bullet? Or at least, more bullet weight? Enter the 77 grain OTM from Black Hills. Not only is this bullet 24% heavier than the standard-issue 62 grain and 40% heavier than the original 55 grain bullet the AR-15 was designed for, but it is also open-tipped. Open tipped bullets have been the standard for self-defense and hunting applications for decades because they work. A deforming, expanding bullet replicates the characteristics of the soft lead projectiles that dominated warfare world-wide for centuries. In conclusion, the 77-gr OTM rocks from SBRs, right? I don’t think so.

5.56/.223 is velocity-dependent. Even with a heavy-for-caliber 77 gr bullet, it still has a need for speed. Now, as we learned from the post about SBR effectiveness, speed (aka: effectiveness) drops off very quickly as you chop the barrel down. The 77 gr OTM is very heavy for caliber, so it starts off slow.

The bullet construction is an area of concern for me, as the 77 gr OTM is a competition-designed bullet, the ‘M’ in “OTM” standing for “match”. Match rounds are not optimized for use on living tissue. The fact that self defense ammo and match ammo both have open tips is a coincidence, match rounds are optimized to fly as straight as possible and hit steel or punch a hole in paper. What competition bullets do once they reach the target is of no consequence. As you can imagine, that is not what you want in a self-defense round. Hunting and self defense ammo is designed with “what happens after it hits the target?” in mind, like controlling the expansion of the bullet, retaining weight after impact, etc. There is a reason that even today there are different projectiles intended for hunting vs match shooting.

Why did this round even become a choice for SBRs in the first place? I’m not sure. If I had to come up with something, I would assume that its because SOCOM guys who were using mk18’s were not pleased with the performance of their issued M855 ammo (a topic for another day) and figured the super cool sniper stuff would be more interesting. Considering the very low standard they were comparing the 77gr OTM to, I would choose it too, if I only had those two options. As a private individual who has access to the commercial market, I don’t have that limitation..

So, what is the 77-gr OTM? Probably an excellent target shooting load (as the history of the round attests), and probably mediocre in a gel block. Let’s find out.

Testing

I’m using a 6″ x 8″ x 20″ 10% gel block from Clear Ballistics. It’s quickly becoming the industry standard, and it’s cool to look at.

I shot the block one time each with my 12″ AR and my 18″ AR. The pistol’s round went very low, bouncing off the table the block was sitting on, before going back into the gel. It was almost a catastrophe and made photographing the wound track very frustrating. The 18″ rifle shot was dead center and looks excellent.

Interpreting the Results

77 gr OTM out of an 18″ Barrel

Let’s look at the 18″ barrel first.

The majority of the jacket came to rest at 13.5″, and the majority of the core penetrated 14.75″. As you can infer from that sentence, and from the impressive cavity pictured above, the round came apart in the block. I see this as a good thing. The 77gr OTM sent little fragments all over the place. There is a big chunk at 8″, another around 12″, the two I already described, and little pieces here & there.

Now let’s talk about the massive, permanent deformation.

It’s hard to see, but the permanent cavity is 2-2.5″ wide and starts around 2.5″ into the block. It maintains that width until 9.5″. Essentially, it’s a 2″ x 7″ cylinder of destruction and would be a devastating flesh wound.

My opinion? The 77 gr OTM is a very capable loading from an 18″ barrel, at least up close. No data yet on how it’d perform at distance in gel (stay tuned).

77gr OTM out of a 12″ Barrel

The round penetrated the same depth of 15″ like the longer barrel, but what it did in the process is the real story. While it looks nasty, the cartridge didn’t perform as spectacularly out of the shorter barrel. The two biggest differences are the lack of permanent cavity and increased early fragmentation. The lack of permanent cavity is due to the lack of velocity I noted above. The 77gr doesn’t have enough runway in a 12″ barrel to get up to speed, and performance suffers. The bullet somewhat ice-picked through the gel at the slower speed, not nearly causing the same kind of damage as it did from the longer barrel.

The bullet did fragment and send even more little pieces out into the gel than it did from the longer barrel, but I’m not sure how much stock to place in those fragments. The bullet bounced three times off the metal surface where the block rested — once at 2.25″, again at 6.25″, and lastly at 11.5″. The fragmentation from the short barrel happens immediately following the first two bounces, leading me to believe the bullet would have held together longer if I had hit the block more towards the center. The very short distance the small fragments traveled away from the main bullet path also leads me to believe they would have very little wounding capacity in flesh, and not contributing much to the bullet’s effectiveness. A few of the small fragments got 3 or so inches away, so they might have had a positive effect.

Conclusion

Obviously, I think this round rocks out of the 18″, which makes a lot of sense considering it was developed for the 18″-barreled mk12. It might still be good out of a 16″-barreled ‘do-all’ gun, but I don’t think I’d be very impressed by the performance in gel out of anything shorter. The lack of permanent wound cavity alone would keep me from recommending this round for sub-16″-barreled guns, but that’s not the only reason.

Something else different that I hadn’t realized until I started writing this is that the faster bullet traveled straighter than the slower one. The slow bullet almost escaped the block three times, whereas the faster one penetrated very straight. Imagine this kind of behavior in a self defense scenario. I want my bullets going exactly where I put them, not veering off course! Now, I don’t know if this is a one-off fluke or a common occurrence, but it doesn’t sit well with me. Just one more reason I wouldn’t recommend this round for dudes running sub-16″ guns.

Will this bullet get you killed in the streets? No. Anything coming out the end of a 5.56/.223 gun will ruin a person’s day, especially if it’s followed by 4-8 of its friends in quick succession, but there’s no reason we can’t make each bullet effective. This round is wonderful out of a longer barrel because that’s what it’s designed for: precision work at high speed (from a ~20″ barrel). Dropping this into a 12″ SBR and expecting it to retain it’s incredible performance is just not logical.

I’m certain there are loads out there that perform much better from the increasingly common pistol/SBR length barrels we see these days. Now that I have a gel block and a place to shoot it, I plan on finding some of them.

Stay safe, stay tuned, and don’t believe everything your read on the internet.

Except this blog, believe us. But not everyone else.

-S_S

And once again, thank you to Ammo To Go for sending the ammo. Go check them out.