The Kel-Tec RDB Defender is a bullpup, gas-piston semi-automatic rifle chambered in 5.56 NATO. It has a 16.1-inch black nitride barrel and a tan Picatinny receiver with an M-LOK handguard. The stock is collapsible, adding to the already compact bullpup package. 
 

Key Specifications 

• Brand: Kel-Tec 
• Model: RDB Defender 
• Caliber: 5.56 NATO 
• Action: Semi Auto 
• Category: Bullpup Rifles 
• Barrel Length: 16.1 in 
• Capacity: 20+1 Rounds 
• Color: Tan 
• Receiver Material: Aluminum 
   

Detailed Features 

• A gas-piston operating system is used instead of direct impingement for cycling. 
• The M-LOK handguard gives mounting space for lights, grips, and other accessories along the forend. 
• The collapsible stock lets the already-short bullpup shrink further for storage. 
• Ambidextrous safety and a reversible operating handle support both left- and right-handed shooters. 
• Ships with a 20-round magazine for a 20+1 total capacity.

Kel-Tec's RDB Defender draws mixed reaction on build quality. Owners like that the bullpup layout keeps the rifle short for its barrel length, and the gas-piston system runs cleaner than a direct-impingement design. Some buyers of early production runs report needing warranty work, though that has reportedly improved on newer rifles.

Ergonomics are the most talked-about part of owning an RDB. The ambidextrous controls and reversible charging handle earn praise from left-handed shooters, but the trigger pull draws steady criticism as long and heavy. Bullpup balance takes some adjustment for shooters used to a traditional rifle layout, and a few owners find the magazine release position awkward at first.

On value, buyers like getting a compact 5.56 platform in a factory-built package, though the bullpup's aftermarket support for triggers and accessories is thinner than more common rifle platforms.