Caliburn 4 (C4)

(10 customer reviews)


Another great design by CaptainSlug! Pump-action, mag fed, high performance, rigid platform. Great for beginner nerfers or experienced nerfers alike. Darts & magazines sold separately.

Shown as Black
Shown as Purple
Low (140-150 FPS)
Medium (175-200 FPS)
High (200-250 FPS) (+$10.00)
Super High (250-300FPS) (+$34.00)
FPS ranges are an estimate. Performance may vary.
Knuckle Duster (+$9.00)
Lower Stock Spacer
Custom Magwell Text (+$10.00)
Iron Sights (+$4.00)
Rail Riser (+$10.00)
Suppressor SCAR (+$15.00)
Rubber Grip Sleeve (+$10.00)
Aluminum Trigger (+$15.00)
Aluminum Sear (+$20.00)
Aluminum Rambase (+$30.00)
Upgrade Plunger
Adjustable Stock (+$20.00)
Ties with Side Rails (+$5.00)
Colored Flatbars
Plunger Black Acetal (+$21.00)
Plunger White Acetal (+$21.00)
Plunger Aluminum (+$31.00)
RMAX (+$20.00)
Stampede (+$40.00)
Angled Foregrip (+$10.00)
Pyrangle Foregrip (+$10.00)
Modular Vertical Foregrip (+$15.00)
Product total
Options total
Grand total


The Caliburn C4 is a homemade Nerf blaster originally designed by CaptainSlug. Pump action, clip-fed, variable fps. Listing is for an assembled and tested Caliburn C4 blaster. Darts, mags, and accessories sold separately. Color configurator provided by captainslug: Caliburn 4 Color Configurator

*C4 not compatible with K14 spring


  • 1 Fully-assembled & tested C4 blaster
  • Passive Magwell Adapter
  • 1 main power spring
  • Spare screws and hardware for maintenance

Blaster Features:

  • More dry-fire safe than predecessor. Great for beginning nerfers.
  • Quick-access buttplate for easy spring swap to adjust power
  • Compatible with both half and standard (elite) dart types
  • Increased durability & rigidity from the previous versions
  • Compatible with all standard picatinny attachments and Caliburn Lower Stock Spacers
  • All Flat bar construction
  • Tool-free passive talon/nstrike mag adapter
  • Faster spring-swaps
  • Optional air-brake plunger feature
  • Maintains the takedown feature
  • Optional o-ring collet muzzle for fast barrel swaps
  • Supports elastic and extension springs for accessories
  • Higher rigidity mixed-print-orientation grip assembly
  • Still compatible with Tooth-And-Nail and other aftermarket parts



  • Darts NOT included. Darts must be purchased separately.
  • Compatible with standard nerf brand darts, as well as short darts
  • Recommended darts: Worker Gen3 Darts


  • Compatible with most standard picatinny-compatible attachment
  • Compatible with all addons featured on the listing. Not compatible with the threaded rod Caliburn’s adjustable stock

What’s involved in the different power options?

*All FPS ratings are an estimate. Performance may vary.*

LOW | 140-150 FPS
Main power spring: 788
Barrel: 14″ .527

MEDIUM | 175-200 FPS
Main power spring: K25
Barrel: 14″ .527

HIGH | 200-250 FPS
Main power spring: Pro25 Plain
Barrel: 16″ .509

Main power spring: K31 + K25
Barrel: 14″ Brass/Alu Barrel

Special thanks to Captain Slug for licensing his design to us. A portion of sales goes to support Captain Slug.


Additional information

Weight 3.5 lbs
Dimensions 31 × 4.5 × 1.5 in

10 reviews for Caliburn 4 (C4)

  1. J. Franks (verified owner)

    The performance was jaw dropping. I haven’t got any other blaster that comes close to the power of this thing! I ordered a front grip which helps considerably in arming this monster. Also developing better pectoral definition which is an added bonus. Had friends over Saturday and although I had other guns available to shoot, the Caliburn C4 was the only gun they wanted to shoot. Great service and followup. Hats off to the folks at Frontline Foam.

  2. Robert

    I love Frontline Foam! I first discovered them from their insanely useful youtube videos, which were EXACTLY what I was looking for and more! It’s like they could almost charge for it because it’s so useful. I really enjoy my Caliburn C4. I have it tuned so powerful that I can only use it at Airsoft games, which is awesome! I got all those crazy looks and comments like, “You brought a nerf gun???” The referees were blown away that it was so powerful. It really needed a fresh lubricate, but though dusty it still clocked in at 270 FPS! (Wow!) To be honest, I have not hit anyone with it yet, (again, this is vs. airsoft) but Frontline Foam has shared information with me so that I can make it more accurate and more powerful. Looking forward to hitting some elite airsoft guy from 150ft with a nerf gun!

  3. Kyle Smith (verified owner)

    It has been excellent. I wanted something ridiculous and that’s what I got. Almost every time someone new shoots it the first thing they say is “where did it go?!”

  4. Brandon Allred

    I had been looking for an adjustable stock for the C4 for weeks and was extremely grateful to find it here. There were a few things I printed from the set, all worked perfectly. I’ve already downloaded and printed more since yesterday and every piece has worked perfectly so I appreciate it very much.

  5. Chris Carson

    The team at Frontline Foam are passionate about everything dart blaster and their customer service is evidence of that. They scrambled to get my order out last week and it arrived just in time for my match. Sporting a Frontline Foam Caliburn that day was like being Indiana Jones in the sword scene from Raiders of the Lost Ark (1981).

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