Suppressor Guru John Hollister on Subsonic Ammo


IMPACT assigned Sweeney to track down and interview suppressor guru John Hollister. He did just that at SHOT Show, and you’ll find his insights very useful.

At the 2017 SHOT Show, I had a chance to sit down with John Hollister, a suppressor guru who now works for SIG Sauer in it suppressor division. The subject was loading subsonic ammunition, both the factory ammo you can buy, and the ammunition you may be loading on your own.

Sweeney:  John, what is the velocity target that works best for subsonic ammo?

Hollister:  The problem factories have, and reloaders have, is how fast? Velocity is what makes bullets work, and you want as much as possible, but not too much or it goes supersonic, which noise a silencer can’t decrease. We all know what the speed of sound is, but what is the barrel length you’ll be using? If you or the factory loads ammunition to be subsonic, in a 9-inch barreled rifle, for example, how much extra velocity does that load get you out of a 16-inch barrel?

I’ve seen factory ammunition that came too close to the limit, and would have a round or three out of a box go supersonic. And a load that just stays subsonic in that 9-inch carbine, will go supersonic almost every time out of a 16-inch carbine.

In handgun ammunition, it is a lot easier. If it is subsonic in a 3-inch barrel, it is going to be subsonic out of a 5-inch barrel. But, as I said, put that same ammunition into a much longer barrel, and you might have problems. If you are loading your own, you will have to test to be sure.

This isn’t always an easy problem to solve. After all, velocity is what creates expansion, and you want as much velocity as you can, for terminal effectiveness. But no matter how much you want velocity, the speed of sound is not going to adjust to your desires.

Interest in sound suppressors and subsonic ammunition has exploded in recent years, thanks in part to the introduction of the 300 AAC Blackout cartridge.

Interest in sound suppressors and subsonic ammunition has exploded in recent years, thanks in part to the introduction of the 300 AAC Blackout cartridge.

Does SIG look at powders with an eye towards handling the barrel-length problem?

Yes, we carefully select powders with the intention to create the cleanest-burning load we can. There’s not much advantage in making a quiet load, but one that loads up your silencer in short order. At the same time, we try to make the load balanced. That is, as much velocity as we can get in a handgun, and stay subsonic, and still not go supersonic in a longer barrel. A lot of end users have both a pistol and an SBR (short-barreled rifle. Ed.) or a carbine, and they want their subsonic ammunition to be subsonic in all of those.

We look closely at all the powders available, and select the best one for a given caliber and bullet weight, not just in subsonics, but in all loadings. There’s just less wiggle room in subsonics.

So, powder selection is important?

Yes. If you are loading a nominal rifle cartridge for SBR/handgun use, like the 300 Blackout, you don’t have much of a problem. You have to use dense, fast-burning powders simply because there isn’t much room in the case. But, if you were to load something like a .308 Win., and try to make it a subsonic load, you have a huge case with a small powder charge, and that can lead to real ignition problems.

That is the Secondary Explosion Effect, something that was of intense interest in reloading circles a couple of decades ago. 

Exactly. Once the amount of powder in the case goes below a certain percentage, the loading density, you can get all kinds of squirrely things going on.

Well then, can’t someone make special .308 Win. cases, with a decreased internal volume?

That’s been done, but it brings its own problems. Even if you try and mark them, it only takes one case of the wrong type to get mixed up, and you have a big potential situation. Get the decreased-volume case mixed in with your regular ones, throw in the wrong powder, and big problem.

Well, can’t we mark the modified .308 cases somehow, to keep them separate?

Patrick, you and I know that sooner or later, someone will get one wrong case in a loading session, and then things get ugly. We suggested it here at SIG, but the ballisticians weren’t too keen on the idea, and the lawyers looked around for their fainting couches, and for good reason.

Hollister is a wealth of knowledge when it comes to making things quiet, and he points out that loading ammo for silencer use is an exacting process.

Hollister is a wealth of knowledge when it comes to making things quiet, and he points out that loading ammo for silencer use is an exacting process.

So, what can a reloader do, then?

Use the heaviest bullet that there is published loading data for. Use a bulky powder to fill the case as much as possible. Right now, it may not be possible to load your own subsonic .308 Win. 300 Blackout is easy; handgun cartridges are easy. But .308 Win. isn’t. However, I expect the powder makers will come out with published data, once they find safe combinations.

Using heavier than usual, or the heaviest of bullets in a cartridge, and making them subsonic, is there a problem with stability?

Not usually. The twist rate of a barrel determines if the bullet will be stable, and the twist rate is usually faster than even the heaviest bullet for a given caliber needs. That’s something barrel makers have worked on for more than a century now. The example for us is the 9x19mm with a 147-grain bullet. Even a hollow-point bullet with a boattail is stable in a 1:10 twist. The normal velocity for it is subsonic anyway, so specifically loading it to be subsonic in all conditions isn’t going to change that.

Now, if you find a way to load something really heavy, and long, because length is what matters in stability, you’ll find that you can’t fit it into the magazine, or the chamber.

The effect of velocity on bullet stability is a small percentage of the force acting to keep the bullet point-on. For handguns, if the twist was correct for supersonic ammunition, it will be correct for subsonic, even if the bullet is at the maximum normal weight for the cartridge.

Loading subsonic ammunition is more complicated than just dumping a reduced powder charge into a case. A .30-’06 is very tough to make subsonic.

Loading subsonic ammunition is more complicated than just dumping a reduced powder charge into a case. A .30-’06 is very tough to make subsonic.

What about the effect of a heavy bullet on crimp and neck tension?

It is very important. A subsonic bullet is going to have a less-flat trajectory than a supersonic one, and too-wide a spread in velocities can lead to accuracy problems. We see this in particular with the 300 Blackout, where a subsonic bullet of 220 grains, if it has too great a velocity spread, can have vertical stringing by the time it gets to 100 yards.

A heavier bullet has more mass to work on the crimp. It is also longer, which means more leverage. In handgun applications, this isn’t a problem, because again, the magazine limits the length of the cartridge. Our example of a 9x19mm loaded subsonic with a 147-grain bullet, has a finished cartridge that is not appreciably longer than one loaded supersonic with a 124 or 115-grain bullet. The magazine limits the length, and extra weight must be inside the case.

Is vertical spread a problem with traditional handgun cartridges?

Not to as much of a degree, as most shooters aren’t going to be shooting groups at 100 yards with a 9x19mm pistol. However, neck tension is of greater importance, as you do not want bullet setback. Even a small amount of setback in a 9x19mm case can be a problem. The case is so short, and the combustion chamber so small, that any change is magnified. You can easily double the chamber pressure of a 9x19mm cartridge, if the bullet sets back. That would be bad.

So, reloaders should pay close attention to the neck tension of
their ammo?

Yes, and if they can, use a bullet with a cannelure, and crimp into it enough to add bullet pull resistance, without causing headspace problems. At SIG we try to ensure every load has a cannelured bullet, and the case is crimped into it. We have stringent specifications concerning projectile retention and tests to ensure we stay within the specifications.

For those using pistols and rifles chambered in 300 Blackout, this is even more important, why?

A 300 Blackout is designed not to fully chamber in a .223 Rem. or 5.56x45mm NATO chamber. The loaded cartridge is too long, and the bullet won’t let the bolt close and lock. As long as the bolt is held open, the firearm can’t fire. But, if you do not have enough neck tension, or you haven’t used a bullet with a cannelure and crimped into it, the bullet can set back, and the bolt close and lock. While a bullet setback in a 9x19mm is bad, it is far worse in the 300 Blackout in a .223 Rem. chamber. There’s no room for the bullet.


You bet.

Back to powders. How should reloaders approach powder selection, then?

The powder manufacturers are the best source when you are working at the limits. They have tested their powder with every bullet in each caliber that they can acquire. A bullet maker may do that, but their job is a lot harder than the powder maker. And, the powder maker is familiar with their own product, and more-likely to see problems as they arise.

I ran into that some years ago, when I phoned a powder maker about a problem I was having. After listening to the start of my problem, the ballistician interrupted me. “You were using X powder in Y cartridge, weren’t you?” Why, yes. “There’s a reason we didn’t list it in the loading manual. It doesn’t like that cartridge; we have never figured out why.”

Exactly. The powder maker has decades of experience with their powder, and reports from users who have had problems. If they don’t show data for it in a particular application, then there’s a reason. At SIG we carefully select our powders for the most-efficient use with our cases and bullets, but that doesn’t mean that that powder would be the best powder for use with the bullets your readers might select.

What recommendations might you have for someone looking to load subsonic ammunition?

First of all, remember that you are going to be pushing these bullets through a silencer. After all, there’s no other reason to be obsessing over subsonics, other than a silencer. This means you have to have better reloading habits and attention than you might have, without a suppressor. You want a clean-burning load. That means an efficient powder, well-suited to the cartridge you are loading. Obviously, you want to be using a jacketed bullet. Lead bullets can be loaded to subsonic velocities, but a lead bullet is going to crud up a silencer a lot faster than a jacketed bullet, even with a clean-burning powder.

And if you are going to be loading what might be considered a rifle cartridge, like the 300 Blackout, in a pistol, subsonic, and with a silencer on it, pay attention to the twist rate.

John took time out of his busy schedule to answer Sweeney’s many questions, even though he was very busy on the floor of the 2017 SHOT Show.

John took time out of his busy schedule to answer Sweeney’s many questions, even though he was very busy on the floor of the 2017 SHOT Show.

I thought you said that wasn’t a problem?

For regular handgun cartridges, no. But, if we’re working with what are usually rifle cartridges, in a pistol, it can be. For instance, the usual .30 cal. twist rate is 1:10. But, a lot of .308 Win. rifles now come with a 1:12 twist, because it is more accurate with the normal rifle bullets.

If you have a 300 Blackout pistol, built with a 1:12 barrel, a 220-grain bullet, subsonic, is not going to be stable. There’s a reason the regular 300 Blackout firearms are usually made with a twist of 1:8 or faster.

That subsonic 220-grain bullet, in a 1:12 twist, is going to, sooner or later, cause end cap, and even baffle, strikes. That will mean a needed repair to your silencer.

So, should our readers give up the idea of loading their own subsonic ammunition?

No, they just need to know what they are doing. It might not be a bad idea to load standard ammunition for a while, learn the ropes, before loading subsonic ammunition and then shooting it through their silencer. We can always repair or replace SIG silencers, if they happen to bust it, but with a little learning and care in loading, they won’t need to go to that expense.

There’s always the option of just buying factory-new subsonic ammunition, isn’t there?

Well, yes. The bosses would not be happy if I didn’t point that out, and we do make good ammo, or so I’ve heard.

Yes, I’ve had no complaints with SIG ammo, subsonic or supersonic, but money is money.

It certainly is. It takes practice to build skills, and while dry-fire practice is good, at a certain point you need to bust caps to verify the skills you’ve built.

John, thanks for the info.

You’re welcome Patrick, and any time you have questions, about ammo in general, or SIG ammo in particular, give me a call.

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