Subsonic 22 Rimfire Ammunition
by Peter Cronhelm
Subsonic .22 Rimfire Ammunition
What is the quietest possible shot using a conventional weapon and ammunition? The lowly .22 rimfire, bolt-action rifle fitted with a modern suppressor and subsonic ammunition wins the contest with sound pressure levels (SPL’s) hovering around 110 dB depending on the ammunition.
Action noise is nothing more than the fall of the firing pin, the long barrel helps mitigate gas pressure and temperature and the suppressor is left to peel off the remaining muzzle signature. The shot is effectively reduced to the noise of the firing pin drop, which is as quiet as it gets.
With this class of weapon, bullet impact is the dominant sound associated with firing a shot. From behind the butt, the experience of squeezing off a shot is surreal. Without any type of hearing protection, all the shooter hears is a soft “click” as the firing pin crushes the case rim … and then the distant thud of the bullet hitting home.
The only real variable in this recipe is ammunition. And as most shooters are aware, not all .22 ammunition is created equal. This goes doubly so for subsonic .22 ammunition.
For this article, a variety of commercially available subsonic-labeled ammunition was tested for accuracy, velocity and consistency. Most serious rimfire shooters undoubtedly know that all .22 rimfire Match ammunition is inherently subsonic. However Match bullets are generally solids, which are not always appropriate for taking small game or tactical targets. Subsonic ammunition generally employs conventional hollow point projectiles more suited to live targets.
Two rifles were employed for the testing to ensure that one did not favor any specific brand. The rifles were a nearly new, factory spec, Anschutz 64M and a lightly modified Valmet (Finnish Lion) Standard ISU rifle. Both rifles are heavy barreled target models with light match triggers. These rifles are capable of excellent accuracy with a variety of ammunition, ensuring that any loose groupings are the result of the ammunition and not the rifle.
Both rifles mount identical optics setups. Tasco 3-9x40 MIL Dot scopes wearing a Stoney Point target knob on the elevation turret. The scopes are mounted in Burris Signature Zee rings.
Tactical operators often utilize handguns as well so additional accuracy and velocity data were gathered using a Ruger MKII target pistol. The Ruger is the defacto industry standard against which all other target pistols are compared.
Velocity was measured with a Chrony chronograph and is the average of ten shots. Rifle velocity data was collected from the Valmet with its 20 inch barrel. The Ruger pistol was the 5.5 inch barrel model. Both average velocity and standard deviation were calculated for each ammunition type.
Standard Deviation is a statistical measure of the consistency of the measured velocity. That is, ammunition with very uniform velocities will have a low standard deviation. Velocity spread is an indicator of accuracy, especially over longer ranges.
Rifle groups were shot off a benchrest grade rest and bags at 50 yards. Average group sizes were calculated from three, five shot groups per rifle. Five shot groups are a much better statistical indicator of consistent accuracy than the more commonly quoted three shot groups.
Pistol groups consisted of a single, ten round group fired at fifteen yards. A benchrest was utilized to ensure groups were as tight as possible.
Three fouling shots were fired at each ammunition change to give the bore a chance to acclimatize to the new round. Rimfires can be sensitive to ammunition type. The Anschutz proved to be especially sensitive to bore condition. In several cases it was possible to see the groups shrink as each was fired. In this case, the first group was thrown out of the accuracy data.
Ammunition tested includes: Remington Subsonic, Lapua Subsonic, Eley Subsonic, PMC Moderator and Aguila SSS.
Remington Subsonic is the old man of the test as it has been available for years while the others are relatively new to the scene. The Lapua is by far the most expensive ammunition of the test. PMC Moderator is the newest kid on the block while the Aguila SSS is the weirdest kid in the neighborhood.
Being unlike any of the others, the Aguila SSS deserves its own paragraph and a bit of an explanation. This is truly specialty ammunition designed to take larger game with less muzzle report. It has a very large 60 grain bullet (50 percent heavier than a normal .22 bullet) stuffed into a .22 short case, only leaving room for a small powder charge. The result is a very quiet round with the ability to carry hitting power far beyond that of conventional .22 rimfire ammunition. The large bullet can penetrate deeply enough to take deer sized game out to 100 yards with proper bullet placement (Paulson).
The major issue with this ammunition is rifling twist rate. The large bullet typically requires faster than normal rifling twist (1:16) to be properly stabilized. Meaning accuracy can be a problem unless a custom barrel is employed.
Aguila SSS will function all semi-automatic actions yet it is spooky quiet through a suppressor. It can be difficult to find in stores and a bit expensive when it is found but is worthwhile tracking down if the quietest possible shot is the ultimate goal and the cost of a custom barrel is not an issue.
The Finnish “Gunwriters on the Web” website notes the following about Aguila SSS: A notable fault of .22 SSS is too thin (if any) lubrication of the extra-long/extra-heavy bullet. The projectile acts as a "compression bullet". A sudden thrust of chamber pressure expands the bullet into the bore. It is beneficial for accuracy of shooting, but tends to cause leading of the bore; especially in the muzzle end of barrel with a length more than 24" (61 cm). Lead fouling may cause the "precession" (yaw) of bullet, already just marginally stable because of too slow rotation. If the rifle shoots nice round holes to 50 yards/meters when cleaned, but starts to produce the "keyholes" after a dozen shots, lead has accumulated in the bore. You may try to "dip lube" the bullets in a melted bullet lubricant. Bullets of .22 SSS have ample "cannelures" or lube grooves knurled around to receive the dip lubricant. Worthwhile information for those who want or need to use this ammunition in quantity.
Velocity Data RIFLE HANDGUN
|Ammunition||Average FPS||Standard Deviation FPS||Average FPS||Standard Deviation FPS|
|Winchester Power Point||1269||22.2||1050||24.7|
Winchester Super-X Power Point was included in the velocity and accuracy data because it is the ammunition the author has used for small game hunting for the past several years and it is a good representative of standard high velocity ammunition. It was chosen for use in the author’s rifle after extensive accuracy testing of many different types of hollow point hunting ammunition.
|Ammunition||Avg. Group Size (Valmet)||Avg.Group Size (Anschutz)||Group Size (Ruger MK 2)|
|Winchester Power Point||0.592"||0.952"||1.041"|
As can be seen from the velocity and accuracy data, you get what you pay for. The Lapua is by far the most expensive ammunition and it shows with an average group size a third smaller than its best competition. This is also reflected in the standard deviation, which is the smallest of all those tested. However, if cost is a factor, the Lapua is 50% more expensive than the next most accurate ammunition. The Lapua was quieter than its velocity might indicate.
The next most accurate ammunition was the Eley, which is a solid, and as such is not very appropriate for hunting any type of game. The Eley also suffered from a tacky lube on the cases, which made them sticky in the test rifle’s match chambers. Eley Subsonic is also saddled with being more than twice as expensive than conventional 22 hollow point ammunition. Eley apparently makes a hollow point subsonic ammunition that is devoid of the tacky lube however a box could not be procured in time for this test.
For use with a suppressor, both the Eley and Lapua operate pretty close to the transonic range. The sonic crack is not generated at exactly the speed of sound. The sound increases in volume across the transonic range starting about 92-93 percent of the speed of sound based upon research by Al Paulson. Also keep in mind that a sound suppressor (silencer) may create about 30 fps of freebore boost. Testing for this article was performed at over 4000 feet altitude where the speed of sound hovers in the 1050-1100 fps range depending on temperature.
PMC Moderator, the newest ammunition of the type, was third on the accuracy list and grouped slightly better than the Winchester Power Point control. Price wise it is exactly the same as Winchester Power Point and Remington Subsonic. Specifically designed for use through a suppressor, PMC Moderator clocked in at just under 1000 fps making it outstandingly quiet through a suppressor. Shooting this ammunition through a suppressor never seems to lose its entertainment value.
Remington Subsonic was a known quantity going into this test as it had been used many times previously in both rifles. The biggest complaint with the Remington is that even though it averages just inside the speed of sound; about 30-40 percent of the rounds are transonic out of a 20 inch barrel. This is unacceptable for use with a suppressor because the sonic crack is as loud as a high velocity round. A semi-auto action soaks up just enough energy to reduce the Remington’s velocity below the transonic range but then you have the clatter of a cycling bolt.
Aguila SSS performed less than optimally in the rifles due to the conventional 1:16 twist rate. Other tests, using faster twist rates have shown excellent accuracy from this round. Actually, the performance captured in this test, particularly from the Anschutz rifle is remarkably good because generally the 1:16 twist rate doesn’t properly stabilize the bullet, resulting in terrible accuracy. Performance of this round through a suppressor simply has to be experienced to be believed.
Pistol data generally followed that from the rifles but with a few surprises. Remington Subsonic, which got nicknamed “Remington Transonic” in the rifles, was an absolute star in the handgun, only bettered by the ultra expensive Lapua and then only by a hair. The Aguila SSS also performed much better in the handgun than it did in either rifle. The Eley and the PMC Moderator just didn’t seem to like the Ruger pistol and both performed below expectations.
A liability with the PMC Moderator was its tendency to cause the pistol to cycle incompletely when it got dirty. This resulted in various jams and failures to feed or extract. Not a problem if you clean regularly but a big problem if the gun goes a while between cleanings. This is such a problem for the author that we don’t use Moderator in the pistol anymore because it takes the fun out of the shooting.
All the tested ammunition was subsonic from the short pistol barrel, even the high velocity Winchester Power Point, although it is a little too close to the transonic range for comfort. Aguila SSS averaged less than 800 feet per second, which would be way too slow if it wasn’t for the huge 60 grain bullet’s ability to penetrate.
The outright winner of the test has to be the Lapua Subsonic due to its outstanding accuracy and consistent velocity. However, for shooters on a budget, PMC Moderator looks like the next best choice. It is accurate enough to do the job and its sub 1000 feet per second velocity ensures it will not produce a loud ballistic crack just when a stealthy shot is required. This stuff is specifically designed to be used through a suppressor and it shows.
An issue that afflicts all subsonic ammunition is the change in point of impact when changing from a high velocity brand. With the more conventional subsonic brands, this is generally a matter of an inch or two at the most. However the Aguila SSS tends to drop to a much greater degree due to its abnormally heavy bullet and very slow velocity. A rifle really needs to be dedicated to this round to avoid a zeroing error when switching ammunition. However, for the ultimate in rimfire stealth and hitting power, Aguila SSS has no competition.
Don’t forget the Golden Rule of rimfires. Every rifle will like a different ammunition so they have to be tested together and once a good combination is found, buy a case or two.
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