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, which keeps unloaded weight at 107.2 oz on a bullpup that would otherwise carry the mass of an aluminum upper plus barrel set behind the grip. The 1:7 twist rate stabilizes heavy 77gr match ammunition. Kel-Tec specs the RDB's single-stage trigger at 4.5-5.5 lbs, 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
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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.
Does the polymer receiver flex under load?
The RDB uses a polymer lower receiver and a full-length steel top rail for optic mounting. Owners on KTOG and r/KelTec report no measurable flex under sustained or suppressed fire, and the polymer lower is part of how Kel-Tec keeps the rifle around 107.2 oz (6.7 lbs) — noticeably lighter than aluminum-receiver bullpups like the Tavor X95 at 126.4 oz. Mount optics to the steel top rail rather than directly to any polymer surface for repeatable zero.
How does the RDB's trigger compare to a standard AR?
Kel-Tec specs the trigger at 4.5-5.5 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.
