This experiment all started, because I found this really nice little (very little) chunk of public land just a few miles from home. I checked it out, and I could legally hunt there, but it is unfortunately close to a neighborhood. It just didn’t seem right for me to cut loose with my chest thumping loud short barreled 30-06 in that context. I am far to lazy to deal with the paperwork involved in legally acquiring a can (aka: suppressor or silencer), so I started investigating other ways to build a quiet, legal, and (very) big game (up to elk) capable rig. I did not know when I started just how quiet I could go, but after thinking about the physics of it, I was curious to try. Turns out, you can make one remarkably quiet indeed; about as quiet as a normal big game rifle with a suppressor on it, actually. Here is the story of how I did it, with some notes on how I could have done it better.
Theory/Back Story/Notes:
First, let’s define what making a gun “quiet” actually means. In the movies, they put a silencer on a gun, and it becomes this little whisper that you can’t hear 10 feet a way. While it is true that that kind of silence can be achieved with suppressors and low pressure loads and small-ish bullets at very low velocities, reality becomes quite a bit different when you’re talking about something with enough horsepower to hurt a 500+ pound animal bad enough you won’t have to track him too far. Even the humble 308 Winchester, when fired through a suppressor, is over 130 decibels (or dB’s). You screaming at the top of your lungs isn’t anywhere near that loud. Also, as I learned during this project, even if the gun is pretty quiet, by the time the bullet is big and heavy enough to lay some sub-sonic smack-down on an elk sized something, the impact of the bullet is loud enough to be audible from hundreds of yards away. So, when I say ‘quiet big game rifle’, I’m talking about something that’s still going to be, at best, as loud as a 22LR when you pull the trigger. As big game guns go, thats stunningly quiet, but as far as actual “quiet” goes, not so much.
At the basic level, there are really just two things that make a gun loud that we have control of. The first, is the super-sonic flight of the bullet, which all by itself generates about 130 to 140 dB. That is already up around the threshold of pain in the ears, and is the reason suppressing a typical big game rifle doesn’t sound like those silencers in the movies. The second contributing factor, is muzzle pressure, or how much pressure is released when the bullet exits the bore. Believe it or not, this is the really loud part. On a typical hunting rifle, that pressure release is over 10,000psi, and this is enough to bring the sound pressure levels up to 160 dB or more. That is loud enough that you can damage your hearing noticeably without much effort.
Fixing the super-sonic crack is as simple as hand loading substantially sub-sonic ammo, which isn’t totally simple compared to normal reloading, but with a little research and care taken to keep yourself safe, is totally doable. This link is a great place to start on SubSonic loading. Fixing the second problem without a can to mitigate the pressure blast, basically just takes some really fast burning powder in small doses, and caliber/component selection geared towards reducing muzzle pressure to a minimum.
To figure out the best way(s) to reduce muzzle pressure, I leaned heavily on QuickLoad. For those who don’t know, QuickLoad is a piece of software which calculates interior ballistics; which is what happens with any given combination of components, in between the time when the hammer drops and the bullet exits the barrel. That allowed me to play with a wide variety of powders, barrel lengths, and cartridge selections, all without ever loading a round or firing a shot. It is just an estimator, mind you, so I would not suggest you use QuickLoad data to determine where absolute max pressure or bare minimum case fill is, but it’s a great way to figure out where the sane middle ground to start at is when you’re reloading in uncharted territory like this.
Moving into deeper theory, case capacity becomes extremely important for making a quiet gun. The less powder you burn, the less expanding gas there is in the barrel, and thus you get less muzzle pressure when the bullet exits. You also get more velocity for less powder when using small cases, so you can still get a decent sized bullet going reasonably fast while using very small charges. Larger diameter calibers and longer barrels are also very useful, because as the bullet travels the barrel, we get a much larger volume of space for the gas to expand into, which also lowers muzzle pressure.
All of which is a long winded way of saying why handgun calibers such as 44Mag, 45 Colt, etc, when fired in rifle length barrels, are pretty much ideal if all we cared about was making it as quiet as possible. Being handgun rounds, there’s also a huge variety of heavy for caliber bullets available that were designed to perform well at sub-sonic impact velocities, which is a huge bonus for hunting purposes. However, most of the things in that class top out around 300 +/- grains of bullet. I expect that would be plenty adequate for deer sized things, but me being form the ‘more is better’ camp (and elk country), I went much bigger, and did my experiments with a 45/70 and 525 grain bullets.
Equipment/Component Choices:
One of the goals here was to do this on the cheap. So, when I ran across a Harrington & Richardson Handi-Rifle in 45/70, new in box, on sale for $199.95 NIB, that was that. Mine has a 22 inch barrel with a 1:20 twist, which is fast enough for what I wanted to do (barely, but it is). To really do this experiment to the fullest capacity of quiet, a much (much) better candidate would be a Handi Buffalo Classic in 45/70, which comes with a 32 inch barrel. But, those were approx $400 guns, and I have a wife to contend with over gun purchases, so I went with the 22 inch version for half the price. It turned out to be more than sufficient for my purposes, and will be much handier to pack around than a 32″ barrel ever would be. I also note that the break-action platform like the H&R is ideal for this game, since you can easily peer down the bore after a shot to confirm/deny if all has gone well (something you should find yourself doing every time you pull the trigger when doing subsonic load development – you will almost certainly at some point find a bullet that failed to exit the bore!).
A quick note on barrel twist rate. The barrel needs a fast enough twist rate to stabilize extremely heavy for caliber bullets at subsonic velocities. Many of the obvious gun choices out there have far too slow a twist rate for heavy bullets fired at sub-sonic velocities. There are a multitude of online calculators to figure out twist rate requirements for any given bullet weight/length, such as this one from JBM Ballistics, so make sure you do a little homework before you make your firearm selection.
Sub-sonic bullets drop very fast, so really anything past about 60 yards, I knew I would need to calculate hold-over. To simplify this, I chose a Sightron S1 3-9 with a Mil-Dot reticle (I simply use the dots for holdover points). I confess, I went with the Sightron mostly because it was the least expensive ($97) non-crap brand of scope with a suitable reticle that was in-stock the day I went looking for one. However, I was blown away by how good it is. I would have been happy with the glass quality, even if it had been a $300 scope. I mounted it up using some solid all-steel Weaver Grand Slam lever-lock rings for easy removal, if I want to play with it using the iron sights someday (and I do).
For powder choice, I went with Red Dot. It’s very suitable for sub-sonic loading for a lot of reasons: it’s very fast burning, it fills a lot of case for not a lot of grains, and as a flake powder, I (perhaps irrationally) feel that the primer lights it up fairly easily compared to stick/ball powders. That’s important, because poor ignition is a good way to initiate the dreaded Secondary Explosive Effect (SEE), and I am fond of having all my fingers and eyes (in good working order). The fact that I already had a pile of Red Dot on hand also helped the decision making process a lot.
Of course, very heavy bullets were a must, and I used 525 grain Hunters Supply hard cast. Again, they were the least expensive and most readily available bullet of similar weight that I could lay hands on the day I went looking for something of their ilk. They are a rebated ogive bullet, which I actually don’t recommend due to the reduced bearing surface and some other technicalities I won’t sidetrack us here to get into, but they got the job done for me. I will also note, that at the low muzzle pressures in play here, cast bullets are much more reliable as far as exiting the barrel than jacketed bullets are. I taught myself this by finding several 500 grain jacketed Hornady bullets stuck in the barrel, but having never found a cast bullet stuck in the barrel no matter how light the charge. Some bullet lube on the jacketed bullets would probably solve that, but I was too lazy to mess with that sort of thing.
The rest of my setup was just basic reloading stuff, Starline brass, CCI Magnum primers, and an inexpensive set of Lee dies. Oh, and a Bore Snake (or other method of swabbing out the bore while in the field). Turns out that doing this sort of thing is a very dirty business, far more so than standard loads, and I found it handy to Bore Snake the barrel every 5 to 10 rounds or so. I don’t imagine it would have hurt anything much had I not, but it made me feel better to do it, so I did it.
Field testing:
In my QuickLoad research, I found that when dealing with loads like these, while there was plenty of middle ground to work safely in, seemingly minor changes in seating depth, bullet weight, and powder charge, were enough to risk Secondary Explosive Effect (SEE) on the one end or overpressure on the other, both of which can damage or destroy you and/or your gun. So on those grounds, I am not going to publish my exact load data, as I have concerns about someone trying “almost the same thing” as I have done but with a different bullet length/weight or other factor that changes case capacity, and not finding out they were out of bounds until they loose a gun or some fingers or worse. I will tell you everything else, though, so that you and a copy of QuickLoad can easily duplicate my results with whatever rig you end up using.
I load the bullets backwards and seated clear down till it’s flush with the case mouth, so that the finished round looks like a wad cutter handgun round. This substantially reduces the combustion chamber size in the 45/70, which helps a lot for subsonic loading. It also provides the largest possible meplat (flat frontal surface area), which means it will do the most possible damage to a critter if I was to plunk it with one of these. Below is a picture that shows a finished round and one of the bullets themselves. That’s a .223 and a .308 brass in the picture for size comparison. These are BIG chunks of lead, am I right?!
Using my QuickLoad data, I loaded up rounds with the following muzzle pressures as noted below (muzzle pressure is QuickLoad estimate, may not be exact). I have noted by each one, my general impression of sound volume. I do not have access to a dB meter, but I have given my subjective estimate of the dB using This Page for my reference.
500PSI, which showed 740FPS on the chronograph. Wow, that was really quiet! I would describe the sound as more of a ‘pop’ than a ‘crack’, and it did not cause any pain in my ears. It was a funny sound though, in that I felt it was a bit louder than a 22LR, but it lacked that sharp ‘crack’ that makes me wince when I shoot a 22LR without hearing protection. Or to put it another way, it seemed to lack the high frequency component of a typical gunshot. It was also quiet enough that I could (very) easily hear the sound of the 525 grain bullet impacting the tree about 30 yards away that I used for my target (an extremely impressive ‘crunch’, I might add). Based on the descriptions of relative sound levels in the aforementioned chart, I’d guess it somewhere between 130 and 140 dB. For reference, a 308 Winchester through a can would be 135 dB give or take, so this is right on the money for what I set out to accomplish – to make this as quiet as a traditional hunting caliber when fired through a can.
550PSI, which showed 770FPS at the chrono. It was enough louder than 500PSI to notice it was louder. Still lacking that high frequency component, and still did not make me wince. I’d guesstimate it maybe 3 to 5 dB louder than 500PSI, which would estimate it at around 140 dB (+/- 3 or 4).
620PSI, which showed 800FPS on the chrono. This was easily enough louder than the last test to notice it was louder, and now was starting to sound a bit more like a ‘crack’ and was almost (but not quiet) enough to make me wince. As this was right on the edge of hitting the threshold of pain for me, I’d guess this up near 150 dB (.410 shotgun territory).
I went back later with some loaded at 940PSI, which was 950FPS QuickLoad estimates (I didn’t chrono this one). This was starting to get fairly loud, and the ‘crack’ was enough that my ears were starting to tell me they’d rather I not do that too many times without hearing protection. I’d guesstimate these as probably over 150 dB but still substantially quieter that gut-thumping boom of a 30-06 or the like.
So, there you have it. Down in the 500PSI, and substantially sub-sonic, is where the money lives for making your gun quiet without a can. If you could get below 500PSI, of course, it would be even better, and you don’t have to get much above 500PSI for the volume to start getting louder fast. If I had sprung the extra $200 or so for a H&R Buaffalo Classic, I would be seeing muzzle pressures as low as 350PSI. 350 PSI of muzzle pressure should be very noticeably quieter than my experiments above, but not enough so to make me care that much. What I’ve got here is plenty quiet enough to accomplish my purposes.
I would also note, that at these low muzzle pressures, if you did happen to put a sound suppression device on the end of the barrel (such as an EconoCan), I would expect it to be very near ‘movie silencer quiet’. However, there’s no helping the fact that 525 grains making impact is not even remotely quiet (it is in fact, satisfyingly ‘crunchy’), so I will personally not bother.
Additional research I’ve done at other times:
308 Winchester, 200 grain bullets, 1400FPS, 2500PSI muzzle pressure = about as loud as 22WMR (22 Magnum) – one round won’t make you deaf, but 3 or 4 would leave your ears ringing for a bit. Still at least half as loud as full-throttle 308 loads.
308 Winchester, 200 grain bullets, 980FPS, unknown PSI muzzle pressure (my older version of QL didn’t have Trail Boss listed) = almost exactly as loud as the above, but not as ‘sharp’ in the ears due to the lack of supersonic crack. Still would not want to shoot many of these without hearing protection.
9mm Luger, Pistol, 125 grain bullet, 950FPS, 3500PSI muzzle pressure. This was about the same as the second 308 load listed above.
9mm Luger, Pistol, 125 grain bullet, 1200FPS, 6500PSI muzzle pressure. This was way louder than the 308 and 9mm loads listed above.
9mm Luger, HiPoint Carbine, 150 grain bullet (yes, 150), 900 FPS, 450PSI muzzle pressure. This wasn’t bad, actually. I’d say it’s about as loud as my 45/70 experiment. Makes me think that if I wanted a semi-auto that was pretty quiet, a 45ACP with some 260 grain bullets, and some Red Dot loads would be as close to ideal as you could get without getting into NFA toys.
9mm Luger, HiPoint Carbine, 120 grain bullet, 1200FPS, 800PSi muzzle pressure. This was a good way to hear about how loud just a super-sonic bullet was, since muzzle pressure was still pretty low. It was louder than I’d like to shoot a lot of without hearing protection.
Footnotes:
For more info on sub-sonic loading, you can start here: http://members.shaw.ca/cronhelm/DevelopSubsonic.html.
QuickLoad can be had here: http://www.neconos.com/details3.htm
Your comments, critique, and feedback is welcome. Unless you think I’m a total idiot, in which case you can zip it. 🙂