SHORT & SWEET
Some are calling Kel-Tec’s RDB revolutionary. Our author calls it a very worthy home defense weapon.
Is a Worthy Home Defense Weapon
Kel-Tec’s middle name is innovation. The Cocoa, Floridabased company has long been known for innovative polymer firearms. From the P3AT and PF9 pistols, SU-16 rifle, SUB2000 carbine, KSG shotgun, RFB and RDB bullpups to the upcoming KSG-25 shotgun and RDB Survival bullpup, Kel-Tec has always thought outside the box.
The RDB (Rifle, Downward-ejecting, Bullpup) in 5.56x45 NATO came on the heels of the RFB (Rifle, Forwardejecting, Bullpup) in 7.62x51 NATO, in 2015. They started with the design of the RFB and made it less complicated, with the same result, the empty casing ends up at your feet.
One of the drawbacks of a traditional bullpup design has always been that if you shoot it weak side, the brass will eject in front of, or into your face. That is not the case with the RDB. The RDB is a polymer-frame, semiautomatic, magazine-fed, bullpupstyle rifle chambered for the 5.56x45 NATO round. Its revolutionary design ejects spent casings out of the bottom of the receiver, onto the ground at your feet. It is light, maneuverable and well-balanced, with its center of gravity over the pistol grip. Controls are ambidextrous and well-laid-out. Other than a somewhat long take-up, the trigger is quite good. Gas siphoned off the barrel, as the bullet passes the gas port in the barrel, operates a short-stroke piston, that in turn, forces the bolt carrier to the rear. This action causes the bolt, which looks similar to that in an AR-15, to rotate and unlock from the lugs in the barrel extension. The spent cartridge is extracted from the chamber by the extractor, which is in the 6-o’clock position on the bolt face. With the casing angled downward due to the position of the extractor, dual plunger ejectors (at the 2- and 10-o’clock positions) exert pressure on the casing as it moves rearward until it clears the magazine and is forced out from under the extractor claw and down the ejection chute. During its rearward movement, the bolt carrier also cocks the hammer.
The bolt carrier rides along the action spring rod, compressing the action spring as it moves to the rear. Once rearward travel is complete, the action spring causes the bolt carrier assembly to move forward, stripping a round from the magazine and pushing the bolt into battery, chambering the
The positions of the extractor and the ejector plungers, and strength
of the plunger springs, are the keys to the downward ejection of the spent casing. This system must also be strong enough to eject a loaded round that is much heavier than an empty casing. There is nothing else to assist the casing on its trip along the ejection chute.
A forward mounted, non-reciprocating charging handle is located above the handguard. The spring-loaded lever folds forward along the upper receiver when not in use. This lever can be easily moved from one side to the other to accommodate both right- and left-handed shooters. Like an HK MP-5, when the cocking lever is pulled to the rear, it can be rotated about 35 degrees up to lock it into place. Once a loaded magazine is inserted, the lever can be slapped down and a round will be chambered. There is also a bolt release on each side of the rifle, above and to the rear of the magazine well, so that the bolt can be released quickly with either hand during a magazine change.
An ambidextrous magazine release is located behind the pistol grip and in front of the magazine well. It is pushed to the rear to operate. This position allows it to be operated by the index finger (making the magazine change) or by the base of the thumb of your trigger finger hand. If the operator has large hands, it may be possible to inadvertently hit the lever and drop the magazine. This was not a problem for me. By Murphy’s Law, this is bound to happen at the most inopportune time!
The ambidextrous safety is located above the pistol grip, slightly farther to the rear than on an AR-15. It operates in a short, approximately 45-degree arc rather than the 90-degree arc found on most AR-15s. It is easily operated by either the thumb or the trigger finger.
Kel-Tec recommends adjusting the gas regulator for the particular ammunition that you are using, then continuing to use the same type of ammunition. The rifle is adjusted at the factory to function properly with M193-type ammunition. When adjusting the gas regulator, increase the amount of gas by turning the regulator counterclockwise (looking from the rear of the gun) until it cycles properly. Then, for reliability and variations in barrel gas pressure, increase the gas by one more click.
Unlike other bullpup-style rifles that I have shot, the stock trigger in the RDB was quite good. There was an approximate 0.085-inch take-up, but there was no sloppiness in the linkage and no detectable over-travel. The trigger broke at an average of 5 pounds, 9
“I FIRED THE RDB IN VARIOUS POSITIONS … TO DETERMINE HOW WELL THE EJECTION SYSTEM WORKED. IT KICKED THE SPENT CASINGS OUT SMARTLY IN ALL POSITIONS.”
ounces for 11 consecutive pulls, using a Lyman digital trigger scale. At the time this article was written, the RDB was the only model that was readily available. An RDB Survival model was shown at the NRA show and should follow soon. The RDB-C (California compliant) version will follow the Survival model. Finally, an RDB chambered in 6.5 Grendel has gone through engineering but has not yet been green-lighted for production.
Accessories, sights and scopes that will fit on a Mil-Std 1913 rail will be right at home on either the milled top rail on the receiver or the molded rail on the bottom of the handguard. Typical AR-15-style triggers, stocks and handguards will not fit the RDB. Kel-Tec requires the use of NATO (5.56x45) or SAAMI (.223 Rem.) specification ammunition. They also recommend trying various types of ammunition to see which one performs the best, then sticking with it. The use of reloaded, remanufactured or foreign or military surplus ammunition of unknown or questionable quality is not recommended. The use of such ammunition will void the warranty.
During range evaluation, I used ammunition produced by various manufacturers in full metal-jacket, hollow-point and boattail hollow-point configurations. Bullet weights ranged from 43 to 77 grains. All the ammunition used functioned flawlessly and ejected cleanly. Over 350 rounds were fired during this portion of the review. Various brands, types and capacity magazines were used during testing. These included Magpul PMAG Gen M3, C-Products Defense, Daniel Defense 32-round, aluminum GI 20-round and 60-round Surefire magazines. All func-
tioned properly and all but the C-Products Defense and Surefire magazines dropped free at the touch of the magazine release. When performing a tactical reload on a closed bolt, make sure to firmly seat the magazine. Some magazines seemed to be more finicky than others during this maneuver. For accuracy testing, I installed a Nightforce SHV 4-14x50 F1 riflescope, using Nightforce’s 30mm Ultralite Unimount 20 MOA rail mount with a bubble-level
top ring half. This setup worked well.
I mounted an EOTech model 553 holographic sight on the top rail for CQB work. If you mount a red dot or holographic sight on the RDB, make sure that it is high enough to see through comfortably. With the straight stock of the RDB, it is difficult to get your eye low enough to see through low-mounted sights or optics. The RDB is simple to field strip, certainly no more difficult than a piston-operated AR-15, once you have done it a couple of times. Prior to field stripping the RBD, make sure that it is unloaded, the magazine is removed and that there is no ammunition in the area. Follow the instructions in the “Safety, Instruction and Parts Manual” for detailed disassemble and assembly instructions.
Two semi-captive pins pretty much hold the RDB together. Be careful with the pins. The manual says that they are captive, but they will come out. The only remotely difficult part of disassembly/assembly is aligning the three pieces when you insert the pins during assembly.
I cleaned the RDB thoroughly prior to any shots being fired. During the accuracy and velocity evaluation, the rifle bore was cleaned every 45-50 shots. The RDB was a pleasure to shoot. It handled fluidly, and recoil was negli-
“IT HANDLED FLUIDLY, AND RECOIL
gible. Even after shooting an AR-15 for 20 plus years, I found the controls of the RDB easy to adapt to and operate. The only thing that took a little getting used to was the forward charging handle. I kept reaching to the rear looking for my BCM charging handle.
Accuracy and velocity evaluation was performed by firing three strings of five shots each, at 100 yards for each type of ammunition used. The average for three five-shot groups for each of eight different factory loads were within 0.31 inches of each other. Hornady’s 8026 75-grain Match BTHP had the smallest average for three five-shot groups at 2.27 inches. It also had the second smallest single group at 1.48 inches. In second place was the Federal Premium 223R 43-grain Speer TNT Green load at 2.36 inches. Fiocchi’s 223MKC 69-grain MatchKing tied for second place. The IMI 5.56x45 77-grain OTM, LR Mod. 1 load had the smallest single group at 1.42 inches. The RDB isn’t a tack-driver, but then, it isn’t designed to be one. What it is, however, is consistent. It is a close-quarter battle rifle and does a good job of it.
To determine how well the ejection system worked, I fired the RDB in various positions, including upside down, left-side down and right-side down. It kicked the spent casings out smartly in all positions. There were no feeding or ejection problems encountered at any time during the evaluation. When firing in the normal, upright position, it was nice to have the brass land at your feet and not have to go looking for it across the range when it came time to clean-up.
When moving while shooting both strong and weak side, the rifle handled well. When shooting weak side, it was nice not to have brass ejected in front of my face. The trigger wasn’t a Geissele, but it was still very good for this type of rifle.
One safety issue must be mentioned. When checking to make sure that the rifle’s chamber is empty, it is not really easy. The only way to see the chamber is to remove the magazine (which you should do anyway), invert the rifle while keeping it pointed in a safe direction and look up through the magazine well. Even then, you must have direct sunlight or a flashlight to illuminate the magwell and chamber. I regret that I was up against a deadline and was unable to run the shoot house with the RDB. That would have been fun, and I’m sure that the RDB would have performed well. This is a well-balanced and easy-to-manipulate rifle. A loaded magazine counterbalances the heavy barrel, making it handle well. The RDB certainly has adequate accuracy for distances en-
countered in and around your home. There are many opinions regarding what makes a good home defense weapon. The two most important factors are reliability and familiarity. When things go bump in the night, you need to know how to operate your weapon without thinking about it and you need to know that it will fire, eject and feed every time you pull the trigger. Another consideration is tactics when searching for an intruder in your house. The short length of the bullpup design will help you with proper tactics when “pieing” a corner, going through doorways, and so on.
The bullpup design rifle certainly isn’t the only option for home defense, but it is one worth considering. Look at all options and choose what works best for you. If you decide on a bullpup in 5.56 NATO, take a close look at the Kel-Tec RDB. HD
Top: The handguard has a molded-in Mil-Std 1913 bottom rail and a sling clip attachment hook in the top-front position. The handguard can be detached by removing a single pin located toward the front of the handguard.
The forward opening is the magazine well where the closed bolt can be seen. The rearward opening is the lined ejection chute. The rear of the action spring rod can be seen at the top of the chute.
The magazine release is in front of the magazine well. The bolt release is a small tab the protrudes from the receiver above the magazine well. The right-side safety lever is located above the pistol grip.
The left side of the RDB shows the sling attachment points, the ambidextrous controls and upper and lower Mil-Std 1913 rails.