I’m a big fan of the .300 AAC Blackout (.300 BLK/7.62x35mm) because it gives options not found in any other factory cartridge for the AR-15/M4 platform. The cartridge was developed to provide improved performance from the AR platform with only a barrel change, using standard bolts and gas impingement systems.
Standard 5.56mm magazines can also be used with the .300 BLK, though I recommend a magazine specifically designed for the cartridge, such as the outstanding Magpul® PMAG® 30 AR 300 B GEN 3TM .300 BLK for optimal performance with all cartridges.
The design parameters of the .300 BLK make it the ideal round for shorter barrels (where the 5.56x45mm is especially lacking) and for suppressed applications. Supersonic loads provide ballistic performance on par with the 7.62x39mm, while subsonic loads vastly outperform the 9mm Luger for suppressed applications.
Although the .300 BLK has not been adopted by any military, it is in use by a number of special operations forces around the globe, including the U.S., U.K., and Netherlands.
Gemini Technologies (Gemtech) is no newcomer to sound suppressor design. Headquartered in Meridian, Idaho, the company was founded in 1993 and manufactures sound suppressors for rifles, pistols, submachine guns (SMGs), and personal defense weapons (PDWs), as well as accessories and ammunition. The company is a founding member of the American Suppressor Association (ASA). Gemtech was acquired in 2017 by Smith & Wesson.
The Gemtech GMT-300BLK is a .300 BLK-specific sound suppressor that’s full-auto rated. It’s rated for supersonic and subsonic ammo in down to a 7.5-inch barrel, and is a direct thread-on suppressor, with a 5/8×24 thread. The two-piece design features Gemtech’s patented G-Core® mono-core technology. Sound reduction is 28-30 dB, which is very good for a compact suppressor like the GMT-300BLK.
The suppressor has the Gemtech logo on the front, with a 3/8-inch socket so you can easily torque it down. Another cool thing about the design is that it makes cleaning a snap. It’s completely user serviceable. You can easily remove the tube to clean the core.
When installing the GMT-300BLK, Gemtech recommends tightening the core to the barrel and then hand tightening the tube to the core.
Designed for short-barreled rifles (SBRs), the compact GMT-300BLK features all-titanium construction to keep the weight down. It measures 7.5 inches long, 1.5 inches in diameter, and weighs 14 ounces. It has a black Cerakote® finish with reduced IR signature. Cerakote is a thin ceramic finish that is very durable and withstands high temperatures.
Gemtech recently provided me with a GMT-300BLK, as well as its American-made Gemtech 187-grain Polymer Tip Subsonic .300 BLK ammo, which is outstanding ammo for suppressed applications. The polymer tip increases the ballistic coefficient of the ammo, as well as greatly enhancing terminal performance by initiating dramatic expansion upon impact.
The suppressor was transferred to C2 Tactical in Tempe, Arizona. Located right off the I-10 freeway, C2 Tactical has been voted Best Indoor Range in Arizona. It has a 25-yard state-of-the-art range with 23 air-conditioned shooting lanes, a new state-of-the-art simulator, full retail store (including NFA firearms), gunsmith services, and much more. It also offers numerous training courses.
C2 Tactical is an authorized Gemtech dealer. They’re great people and have graciously provided the use of the range for my evaluations. C2 Tactical is in the process of opening an additional facility in Scottsdale, Arizona, which will be open by the time you read this.
THE NATURE OF SOUND
Sound is the sensation that’s experienced when the brain interprets vibration within the structure of the ear caused by rapid variations in the air pressure. Sound is commonly measured in decibels (dB).
The specification of the intensity of the sound, as ordinarily used, implies a comparison with the smallest level of sound detectable by the human ear, which is around one dB (0.1 bel). Normal conversation is around 60 dB. The average threshold of pain for the human ear is around 130 dB.
According to OSHA, the threshold for a hearing-safe impulse noise is 140 dB. Without hearing protection, exposure to any impulse noise over 140 dB causes varying degrees of permanent noise-induced hearing loss. It can also lead to tinnitus. Most well-engineered suppressors take the dB level of their host firearm below 140 dB, making those suppressors effective primary-hearing safety devices.
Two types of noise can damage hearing: 1) short-duration, high-intensity noise, such as gunshots, and 2) prolonged exposure to lower levels of noise. Although individual sensitivity varies, many authorities believe that prolonged exposure to noise above 85 dB can lead to hearing damage.
HOW SOUND SUPPRESSORS WORK
Three possible sources of sound from the discharge of a firearm need to be considered when silencing a firearm: the weapon’s report, i.e., muzzle blast; the “crack” caused by a supersonic bullet passing the sound barrier; and the sound from the cycling of the firearm’s action.
The muzzle blast is the most significant source of sound that’s generated by a firearm. A .22 LR handgun generates around 148 dB, a 9mm MP5 SMG 157 dB, and an M16 168 dB.
Muzzle blast is the consequence of the shock waves resulting from high-pressure gases exiting the barrel. If the pressure is reduced immediately before it exits, the weapon’s report will be reduced. Muzzle blast is also reduced by decreasing the velocity of the gases and either absorbing the sound waves or canceling them by interference with reflected waves coming from the same source.
Sound waves behave in many ways similar to light waves. As with light waves, sound waves can be reflected, refracted, diffracted, and scattered. Various combinations of components, such as baffles, spacers, packing material, mesh, expansion chambers, spiral diffusers, pressure relief ports, and wipes may be employed in a suppressor to reduce the noise from a firearm.
The GMT-300BLK employs a patented one-piece baffle system that is highly effective and provides improved gas-flow dynamics that largely eliminate the first-round pop common with traditional suppressor designs, where the first round is often louder than subsequent rounds and there may be a slight flash.
As a suppressor accumulates fouling during firing, its effectiveness deteriorates. Maintenance requirements differ depending on the suppressor. Some baffled systems require nothing more than dunking in solvent to clean out the fouling. Other designs require repacking or replacement of “wipes” at the factory. As noted, the two-piece design and G-Core mono-core technology greatly simplify cleaning of the GMT-300BLK suppressor.
Weapons with ported barrels and integral sound suppressors do not require the use of subsonic ammunition for effective sound reduction. They’re designed for specialized applications that require fully realized sound and flash suppression. Because the suppressor is integral to the weapon, the weapon may not be used in non-suppressed mode.
Muzzle sound suppressors, such as the GMT-300BLK, are more versatile than integral suppressors in that they can easily be removed when sound suppression is not necessary. If subsonic ammunition is employed, muzzle suppressors are often every bit as quiet as an integral suppressor. Because they do not reduce the velocity of a bullet, higher terminal velocities are possible for applications in which a sonic crack is not an important tactical consideration.
SELECTING A SOUND SUPPRESSOR
When selecting a sound suppressor/weapon system, several factors need to be considered, including the operational requirements of the mission in which it will be employed, any special ammunition requirements, cost, maintenance, and any required modification to the weapon. Other considerations include point-of-impact shift between suppressed and unsuppressed, construction, back-pressure, and thread-on vs. quick-attachment system.
Comparing suppressors is difficult unless one has the details as to how the testing was conducted, since the method of testing may vary from manufacturer to manufacturer. U.S. military requirements for testing are specified in MIL-STD-1474C. Has the suppressor been tested and if so, how? Gemtech tests all its suppressors to MIL-STD-1474C.
When you put on or take off a suppressor, you typically see some point-of-impact (POI) shift. There are two types of POI shift: when mounting a suppressor and from shot to shot. POI shift when mounting a suppressor is more impacted by the threads on the weapon than the suppressor. POI shift is not as much of an issue if it is repeatable, as the shooter can easily correct for the shift. POI shift from shot to shot is most often related to the mounting system of a quick-attach suppressor. POI shift with the GMT-300BLK is minimal and repeatable.
Backpressure from the suppressor also needs to be considered. Suppressing a weapon can significantly increase backpressure, which will increase the cyclic rate, causing weapon malfunctions; reduce the service life of the weapon; spit gasses back into the face of the operator; and cause increased fouling.
Suppressors such as the GMT-300BLK, which are designed to control the gasses rather than simply trap them, create much less backpressure than traditional suppressors. There is still backpressure with the GMT-300BLK, but it’s much less noticeable.
As mentioned, the GMT-300BLK is a thread-mounted suppressor. Threading on a suppressor is the strongest, most precise method of mounting a suppressor. They are generally more accurate and less prone to alignment issues and baffle strikes, although thread-mounted suppressors can work themselves loose and out of alignment. Many users use Blue Loctite® on the threads, although it’s not necessary. Thread-mounted suppressors are widely used on precision rifles.
Quick-attach suppressors have advantages over threaded suppressors for certain applications: They allow the end user to more easily switch the suppressor between different weapon platforms, although they generally require the use of proprietary mounts. Gemtech offers both types of suppressors.
Different materials may be employed in the construction of a suppressor. Each has its pros and cons. Suppressor baffles are under extreme stress and the materials used must be matched to the application.
Stainless steel is a common material utilized in suppressors. It is durable, corrosion resistant, and handles heat well. It is also relatively low cost. A disadvantage is weight.
Gemtech opted for titanium for the GMT-300BLK. Titanium is lightweight and durable. The two most useful properties of titanium are corrosion resistance and strength-to-density ratio, which are the highest of any metallic element.
It’s often used where light weight and precision are important, such as in 7.62mm and larger bore applications.
The downside to titanium is that it cannot handle the heat generated by high volumes of fire, as well as suppressors utilizing higher-temperature alloys such as INCONEL®. For the applications for which the .300 BLK is designed, titanium is an ideal choice.
The Gemtech GMT-300BLK is an outstanding suppressor, ideal for short-barreled .300 BLK applications. It’s exceptionally well-designed and well-made and offers superior performance. It has an MSRP of $995.95.
AMERICAN SUPPRESSOR ASSOCIATION
|MANUFACTURER||Gemini Technologies (Gemtech)|
|CALIBER||.30 caliber (.300 BLK)|
|SOUND REDUCTION||28-30 dB|
|FINISH||Black Cerakote with reduced visual IR signature|
|SUGGESTED RETAIL PRICE||$995.95|