Kel-Tec RDB 5.56 NATO
Model: RDBBLK
Kel-Tec RDB 5.56 NATO
Model: RDBBLK
Full Specifications
About This Firearm
Kel-Tec's RDB is a downward-ejecting bullpup that fits a 17.3-inch barrel into an overall length of 27.3 inches. For comparison, every standard AR-15 in this caliber group runs 35-36 inches with a 16-inch barrel. The bullpup layout moves the action behind the trigger, shortening the rifle by nearly 8 inches without sacrificing barrel length. The extra 1.3 inches of barrel over a standard 16-inch AR gives a small velocity bump with all ammunition weights.
The receiver is glass-reinforced Zytel polymer rather than aluminum, and at 107.2 oz the RDB weighs about the same as the S&W Sport III (104.32 oz) despite the radically different platform. The 1:7 twist rate stabilizes heavy 77gr match ammunition. Kel-Tec specs a 5 lb single-stage trigger, which is lighter than most mil-spec AR triggers. The rifle ships with a 20-round magazine rather than the 30-round standard, though it accepts all standard AR-15/M4 magazines.
The downward ejection system is the RDB's most unusual feature. Spent cases eject straight down through a port beneath the action, making the rifle fully ambidextrous without any conversion. Reviewers at InRangeTV and Forgotten Weapons note that this system works reliably but can deposit hot brass on a bench rest or shooting bag if the port is not kept clear. The Picatinny top rail runs the full length of the receiver for optics, and the 1/2x28 threaded barrel accepts standard muzzle devices and suppressors.
Best For
Strengths & Limitations
- The 27.3-inch overall length with a 17.3-inch barrel gives the RDB an 8-inch length advantage over every standard AR in the 5.56 group while providing more barrel length than any of them (most use 16-inch barrels)
- Downward ejection makes the rifle fully ambidextrous without a bolt swap or conversion, unlike standard ARs that eject to the right and require a left-hand upper or deflector for left-handed shooters
- Ships with a 20-round magazine instead of the 30-round standard that every other 5.56 rifle in this group includes, though it accepts any standard AR-15/M4 magazine
- The polymer Zytel receiver is less rigid than the 7075-T6 aluminum used in every conventional AR in this group, and aftermarket accessory compatibility (grips, stocks, handguards) is limited to Kel-Tec-specific parts rather than the universal AR-15 ecosystem
Compatible Ammunition
Find the best prices on compatible 5.56 NATO ammunition.
Shop 5.56 NATO Ammo →Ballistics Calculator
Calculate trajectory, drop, and energy for 5.56 NATO ammunition.
5.56 NATO Ballistics →Where to Buy
No prices available at this time.
Frequently Asked Questions
Does the downward ejection cause problems at the range?
In normal standing or kneeling positions, the brass falls straight to the ground and is not an issue. When shooting from a bench rest or prone with a bag, spent cases can accumulate under the ejection port and occasionally cause a stoppage if not cleared. Owners on the Kel-Tec Owners Group forum recommend keeping the area beneath the port unobstructed. The system has proven reliable in reviews from InRangeTV and Military Arms Channel.
Can the RDB use standard AR-15 magazines?
Yes. The RDB accepts all STANAG-pattern AR-15/M4 magazines, including Magpul PMAGs, Lancer L5, and GI aluminum magazines. It ships with a 20-round magazine, but 30-round and 40-round magazines work without modification. The magazine release is behind the magazine well, which takes some adjustment for shooters used to the AR-15 button location.
How does the RDB's trigger compare to a standard AR?
Kel-Tec specs the trigger at 5 lbs, which is lighter than most mil-spec AR triggers (typically 6-7 lbs). Bullpup triggers historically suffer from long, mushy pulls because of the mechanical linkage connecting the trigger to the action in the rear. The RDB's trigger is better than most bullpups according to reviewers, though it still feels different from a direct AR trigger. Shooters coming from the IWI Tavor X95 (5.5 lb trigger) generally find the RDB's pull similar or slightly better.