Technical Technology: Kreb's' Custom IMS System
March 28, 2018
Do you want an effective flash suppressor or a muzzle brake mounted to your rifle? A pretty basic question to be sure, but it's one you have to answer. The choice, of course, depends on your needs, and for many of us, there may not be a single right answer. One day you might be competing in a match and want every advantage you can get, so you choose a muzzle brake. That night you go hog hunting with night vision where a flash suppressor is the way to go.
Years ago I thought one possible solution would be to have a standard base unit that could accept other quick attach devices. My thoughts never went beyond paper and pencil, but I did share them with Marc Krebs of Krebs Custom (KrebsCustomAK47.com). He had a similar idea and went on to refine the concept not only into a workable system but also into something that looks good while being quite practical.
Called the Interchangeable Muzzle System or IMS, it consists of an effective flash suppressor that acts as a base unit for an entire system of muzzle devices. Different devices can then be quickly attached or removed to tailor performance to the specific needs of the shooter. Most importantly, all this can be done without the need for tools. Just thread them on by hand, and they lock securely into place.
The foundation for the IMS is an open four-prong flash suppressor. It is 2.9 inches long, adding 1.95 inches in total length to the rifle, and weighs 4.5 ounces. Base units are available with common 1/2x28 and 5/8x24 pattern threads to fit a wide array of firearms.
What is unique about this design is it features 24x1.5mm external threads and a spring-loaded detent. This allows you to thread on another device by hand over the flash suppressor and securely lock it into place. To remove you just have to depress the detent and spin it off by hand.
The thread and detent system is extremely simple, but will it hold up to hard use? Some reading this have already noticed the concept seems somewhat familiar. There's a reason for that. The Russians have been using this detent system since they introduced the AK47, so it's battle-tested, and the oversize 24x1.5mm threads were introduced on the 5.45x39-chambered AK74. Krebs has merely taken these well-proven features that have been in military service for decades and added them to a flash suppressor.
Krebs recommends the flash suppressor base be installed by a gunsmith because it needs to be properly timed. Machining without shims is preferable, but it can be timed using shims. However, if you use shims and plan to mount a suppressor, the shims have to be properly aligned to prevent a baffle strike.
The flash suppressor base effectively eliminates almost all muzzle flash- keeping in mind that muzzle flash varies depending upon barrel length, caliber and especially ammunition. That said, I conducted extensive testing of this design using video cameras located at both nine o'clock and two o'clock from the muzzle in almost complete darkness. Using a Kalashnikov rifle with a 16-inch barrel chambered for 7.62x39, flash reduction was excellent.
Included with the flash suppressor is a simple steel compensator. It weighs 1.7 ounces and has an overall length of 2.46 inches and adds just 0.22 inch to the base unit. It threads easily onto the device and features three oval ports at nine, 12 and three o'clock. It is notched at the front to allow a cleaning rod or similar device to be used to aid in its removal if badly fouled. When installed, it aids in keeping the muzzle flat while keeping the flash signature to a reasonable level.
Putting on the Brakes
A better option is to add an effective muzzle brake. Krebs offers two designs machined from Grade 5 titanium and featuring a black DLC finish. The Short brake weighs 1.9 ounces and adds 0.36 inch to the overall length of the flash suppressor. A two-baffle design, it sports a large and small port at three and nine o'clock.
The Long brake weighs 3.1 ounces and adds 1.4 inches to the overall length. This impressive-looking piece sports five baffles and features four large and one small port at three and nine o'clock. Both are handsomely finished and nicely knurled.
These brakes attached and removed easily with the IMS. While the Long looks good, the Short design proved perhaps 75 percent as effective while being quite a bit more compact. As you would expect, both are loud with noticeable blast to the side. Recoil reduction was noticeable, though, and they proved very flat shooting. When your shooting buddies complain about the blast, just spin it off. Krebs says he is also working on a blast diverter.
Price of the IMS flash suppressor with included compensator is only $90. That's a pretty good deal considering you get two devices and the ability to mount a brake and sound suppressor. The titanium brakes are $91 each. While conceived for use on an AK, I run mine on ARs and have been pleased by what they offer.