Perhaps the most popular new cartridge in years has been the 300 AAC BLACKOUT. Shortly after it was made public, I had an opportunity to meet with Kevin Brittingham. At the time, he was still with Advanced Armament Corporation. He gave me the inside story of how AAC came to develop the new cartridge. The 300 AAC BLACKOUT cartridge was the result of a Request for Proposal from a special mission unit within the United States military. The unit wanted a .30 caliber cartridge that would utilize the standard 5.56 magazines and bolt. The RFP also proposed both a sub-sonic round for use with a suppressor and a supersonic round. Robert Silvers, Director of Research and Development for AAC, put pen to paper, or stylus to computer with the following objectives:
- Create a reliable and compact .30 caliber round for the AR platform;
- The round would utilize existing magazines and retain their full capacity;
- Create a sub-sonic round that is optimized for sound and flash suppression;
- Create a supersonic round that matches 7.63X39MM ballistics;
- Provide the ability to penetrate barriers with a high-mass projectile, and
- Provide a lightweight, durable, and low recoiling upper receiver.
The end result is what is now known as the 300 AAC BLACKOUT. The 300 AAC BLACKOUT, or technically 7.62X35mm, has the same rim dimensions and cartridge taper as the 5.56. This was a critical requirement in order to utilize the existing mil-spec 5.56 bolt and feed reliably from a standard 5.56 magazine. The configuration allows a standard M-4 to be converted to 300 AAC BLACKOUT by simply changing the barrel.
A second requirement was to provide the operator with one rifle that could meet multiple mission requirements. Sub-sonic ammunition would allow the 300 AAC BLK to be a quiet and effective CQB platform while delivering a .30 caliber, 220 grain projectile on target. By changing to a supersonic round, the operator could have a fully capable battle rifle, effective to 300 yards and beyond.
Most of the carbine offerings were in two configurations, either an 8” short barrel rifle or a non-NFA 16” configuration. The 9” barrel is considered an ideal length for a traditional direct impingement carbine. I purchased one of the AAC MPW SBR carbines, along with the 762-SDN-6 suppressor. Both have proven reliable and the 762-SDN-6 has performed well with both supersonic and subsonic ammunition. However, the MPW, like most BLACKOUT carbines, is based on the original M-16 design. That design requires a recoil spring housed in a buffer tube extension. This design limits how compact these carbines can be made.
In 2015, SIG introduced the SIG MCX series of carbines and changed the M-16/M-4 world. The MCX utilizes a short stroke piston system with a captured recoil system that is contained within the upper receiver. This allows the MCX family of carbines to be equipped with a number of stock configurations, to include a folding stock. The MCX system has proven very successful and has been adopted by agencies. One of these is the newly constituted unit within the London’s Metropolitan Police Counter Terrorist Specialist Firearms Officer program. As cool as the MCX is, many considered it “just another black rifle.”
Then came the SIG Rattler, the smallest production carbine on the market today. The Rattler uses the MCX operating system along with the same upper and lower receiver. However, the Rattler features a 5.5” barrel and is chambered in 300 BLK. The Rattler became the darling for those in need of a Personal Defense Weapon (PDW) for protective details and covert operations. The Rattler also features an adjustable gas system that allows it to be run with and without a suppressor.
SIG’s SRD762Ti suppressor is the ideal suppressor for the PDW mission. The SRD762Ti is made from Grade 5 Titanium baffles that are precisely welded without the use of an external tube. This allows the 1.75” diameter suppressor to have more volume than traditional designs. It is 9.25” in length and weighs in at just over 18 oz. While ideal for the Rattler, it should be noted that the SRD762Ti is rated for .30 caliber cartridges up to 300 Winchester Magnum. SIG offers the SRD752Ti in both a direct thread and quick detach configuration. The SRD762Ti is a must-have accessory in order to make full operational use of the Rattler.
Over the last several years, there have been whispers that the special operations community, and specific units, have been utilizing carbines chambered in 300 BLK. Reportedly, Black Hills manufactured a 110 TTSX load and a 201 gr. solid copper subsonic load for some of these units. Those who watch the defense industry blogs may have seen several solicitation notices for 300 BLK ammo. Recently, the FBI released a solicitation for ammunition for HRT. It appears that the 300 BLK is no longer just a niche or special interest cartridge.
One of the more interesting solicitations from SOCOM was released in March of this year. The pertinent information is copied below:
Personal Defense Weapon System Sources Sought
The United States Special Operations Command (USSOCOM) is seeking to identify potential sources within the national technology and industrial base with the ability to provide a conversion kit for the M4A1 to create a Personal Defense Weapon (PDW) system:
-Complete Kit to include upper receiver and buttstock kit
-Any tools required to complete an operational conversion
-A light and sound reducing suppressor that can be attached to the system when needed
PDW Kit specifics: The kit must be adaptable to the standard M4A1 lower receiver, any modification to the lower receiver must be reversible and nonpermanent. The kit must be in .300 Blackout (BLK) cartridge, total system weight, including the M4A1 lower in not to exceed 5.5lbs. Length with stock extended not to exceed 26″ length with stock collapsed or folded shall be 17″ (T), 15″ (O) and a height not to exceed 7.5″. The weapon shall be fully functional when collapsed or folded. The kit should include a 5.56mm barrel that can be changed from .300 BLK to 5.56mm in less than 3 minutes. Accuracy shall be 3.0 MOA (T), 2.0 MOA (O) @100 yds. and 5.0 MOA (T), 3.0 MOA (O) @ 300 yds. both in .300 BLK supersonic.
This announcement constitutes a Sources Sought. It is not a solicitation or request for proposal, but an effort to obtain information for planning purposes only.
The ability to convert existing M4A1 carbines to a PDW, chambered in 300 BLK, offers several appealing advantages. First, it is far more economical than purchasing complete carbines. Far more conversion kits can be purchased than complete carbines. Second, the purchase of a retrofit kit presents fewer issues than building a new carbine. Finally, should the receiver be damaged, the conversion kit can be fitted to another lower.
While I had been following the development of the Rattler for some time, I was not willing to go through the entire NFA Form 4 process. This all changed when SIG introduced the Rattler as a pistol. The pistol configuration featured a collapsible arm brace. I ordered one of the pistols with the intention of using it in place of one of my 300 BLK SBRs. Then came the SOCOM solicitation. I contacted SIG and they were able to ship me the conversion kit. I was now in business with a Rattler SBR.
The conversion kit consists of an adaptor block that replaces the standard buffer tube. It is held in place with a large screw and extends approximately 1 ¼” from the end of the lower receiver. The rear of the adaptor block is configured with a Picatinny style rail with three slots.
The other component of the Rattler kit is the side folding stock. The stock has a cross bolt mount that interfaces with the adaptor plate and is secured with a large hex bolt. The folding stock extends approximately 7.5” from the rear of the adaptor and 9.25” from the rear of the upper receiver. The Rattler upper receiver is a direct replacement for the standard M4 upper receiver. It took me less than 10 minutes to convert one of my registered Smith & Wesson M&P SBR lowers to a full-blown Rattler!
I was immediately impressed with just how compact the Rattler is. With the stock folded, the overall length is right at 16.25”! With the stock extended, the Rattler is 23.75” in length. That is still a very short package. The operating system of the Rattler incorporates an easily adjusted gas block for running supersonic and subsonic loads.
For an optic, I reached out to Aimpoint for one of the new CompM5 red dot optics. The CompM5 is the latest generation of Micro size optics but is not in the Micro family. The CompM5 was developed to be a ruggedized optic that can withstand the harshest operating environment. The CompM5 is powered by a single AAA battery and eliminates the issues involved with flying with the CR123 lithium batteries. It is fully compatible with all generations of night vision optics and Aimpoint’s 3X magnifiers. For more details about the upgraded performance and electronics, visit Aimpoint’s website at https://us.aimpoint.com/news/aimpoint-launches-new-compm5tm-sight/
I also installed an extra set of Troy Industry backup iron sights as a secondary means of shooting. The sharp reader will notice several range photos where I have the front lens cover on the CompM5 closed. This was intentional! Shooting with both eyes open, the dot will superimpose itself on the target as with the Armson OEG sights. Armson USA OEG
On the range, I tested the Rattler, from a bench rest, at 50-yards, using the CompM5 and the 3X magnifier. A phone call to my partners at Federal, Hornady, and SIG allowed me to test the Rattler with seven different loads. All bench testing was done with the SRD762Ti in place for both sound reduction and to test reliability. The suppressed Rattler was 100% reliable with all of the loads and, as reflected in the accompanying chart, all loads produced groups less than 1”. For full disclosure, I suffer from astigmatism and even the sharp dot on the CompM5 became pixilated. This made maintaining a consistent point of aim difficult. To offset shooter error, I measured the best three shots out of a five shot group. I found the stock to be incredibly solid and it locked up with no play or shift.
I zeroed the Rattler for the new Hornady 190 Sub-X ammo, knowing that would be my “go to” round for dispatching critters etc. During the range test, the first anomaly I noticed was that supersonic loads had not only an elevation shift from point of zero, but also a very noticeable windage shift. In some cases, the windage shift was as great as 3 to 4 inches from point of aim. The second item I found was that the Rattler would not function subsonic loads without a suppressor. The gun short stroked every subsonic load, regardless of gas setting. I was very impressed with the performance of the SRD762Ti suppressor when using both the supersonic and the amazingly quiet subsonic loads.
I contacted John Hollister, SIG guru and an all around good guy, to see what was going on. John and I have been friends from his days at AAC and he has always been a straight shooter and never shied away from the tough questions. John said that both issues were “normal” for the Rattler. SIG worked very hard to gas the gun properly to run suppressed and unsuppressed, to ensure maximum reliability. A byproduct is that the Rattler will not cycle most subsonic loads without the additional back pressure that is generated by a suppressor. With regard to the shift in impact, John stated that the shift was the result of the different kinetic energy between the different rounds. The supersonic rounds “whip” the barrel differently than the slower subsonic rounds and is not specific to just the Rattler. This shift is predictable and one of the results of designing a small platform to run with bullet weights that go from 85 grains to 200 grains or heavier. Given the true operating parameters of a PDW in a covert or PSD role, it is unlikely that the operator would be changing between to dramatically different loads. Still, it is a drawback that should be understood and accounted for.
If I were setting up the Rattler for a protective detail, or a low profile mission, I would probably zero it with Federal’s 110 grain Solid Copper HP or the Hornady Black 110 V-Max load. In a defensive environment, where keeping the weapon concealed is essential, there would be very little opportunity to install the suppressor if a fight starts. For offensive actions, such as direct action raids, I would probably choose Hornady’s new 190 SUB-X load to run with the SRD762Ti installed. This load has a very low signature when used with a suppressor, and offers improved terminal ballistics over the typical 220 gr. SMK round. Speaking of keeping a low profile, the Rattler fits well in the smallest backpacks and tennis racket cases.
The Rattler is a very mission specific platform that has changed the paradigm of the PDW as we know it. It is compact, versatile, and reliable and is without any real competition in the industry today. For those who choose to go the NFA route, and already have a registered M4 lower, the conversion kit is a great solution. SIG also sells the full Rattler in a SBR model as well as the aforementioned pistol configuration. However, the best option may be the route I took. I can utilize the SBR in my home state and then install the upper on the pistol lower for travel outside the state. Indeed, that seems to be the best of both worlds.
|SIG M4 Rattler|
|SIG 220 gr. SMK||888||854||863||34||0.50″|
|SIG 125 gr. BHP||1692||1662||1676||30||0.60″|
|Hornady Black 110 gr. V-Max||1912||1806||1839||106||0.05″|
|Hornady 190 gr. Sub-X||916||884||895||32||0.55″|
|Hornady 135 gr. FTX||1668||1642||1656||26||0.75″|
|Federal 110 SCHP||1662||1644||1653||18||0.80″|
|Federal 150 gr. Fusion||1455||1447||1451||8||0.80″|
|Velocity measured at 10 ft./Accuracy at 50 yds. Aimpoint Comp M5 w/3X Magnifier|
If you have not given the Rattler a look, I suggest you visit SIG’s pages:SIG MCX Rattler PSB SIG MCX Rattler SBR