Ullr- Pump Action 3d Printed Nerf Revolver

Pictured with this grip: https://www.printables.com/model/1192191-swoopy-afg-for-short-rails and this PCAR: https://www.thingiverse.com/thing:5174583 

THIS WAS MY FIRST DESIGN, AND MAY LACK A LEVEL OF POLISH. THIS IS NOT A BEGINNER BUILD.

I'm currently working on a completely redesigned, substantially improved V2. You may want to wait for that.

Description

Ullr is a compact and lightweight cylinder fed, pump action, Nerf-style blaster. It has an 8 dart capacity, and swappable cylinders.

• Feeds from a swappable, 8 shot cylinder
• Performance over 200fps with a k25-strength spring
• Short and crisp trigger pull
• Less than 500 grams of filament, and less than 700 grams total weight 
  (with recommended print settings)
• Relatively low hardware costs
• Can be printed and assembled in a weekend

Print Information

WARNING: ALL TESTING WAS PERFORMED USING 0.4mm NOZZLES. ANY OTHER NOZZLE SIZES ARE UNCHARTED TERRITORY.

No parts need to be printed multiple times, and the only optional part is the RearRail, which allows attaching picatinny mounted stock. The FrontFrame has a variant with looser clearances on all dovetails.

Supports

FrontFrame and Frame both need supports, on the highlighted faces. I recommend tree supports.

TopRail needs supports on the underside, I recommend regular supports.

Both Braces (Left and Right) need supports on the highlighted face, support style doesn't matter much.

The PumpBlock needs supports between the nub and the rail, as shown in the image below

Other Settings

No parts should need brims, unless you are having adhesion or warping issues.

Most parts should be printed with 4 walls and 15-20% infill. The Plunger, TopRail, Braces, and Sear should be printed solid. MainFrame should be printed with 6 walls. The LowerBrace should be printed with 8 walls and 10 top and bottom layers

General Information

Including supports and recommended settings, the blaster comes out to around 500 grams of filament.

Minimum build area to print all parts is 160mm vertical, and at least 155x175mm horizontally. 

All parts are pre-oriented in their correct printing orientation.

Hardware

Full bill of materials:

• 1x T4 bar 
• 1x 20cm minimum barrel (25-30cm is probably optimal for k25) 
• 1x 4" length 1 3/8 ID x 1 1/2" OD plunger tube
• 2x -123 orings (1x Plunger, 1x Rambase)
• 1x -012 oring (Pusher tip oring)
• 1x 3/8" long countersunk 4-40 screw (For prime bar attachment to Rambase)
• 1x catch spring OR length of 1/8" elastic (3mm elastic should also work) 
• 2x 3/8" (or 5/16”) long 10-32 screws with lock-washer (For prime bar attachment to PumpBlock)
• 4x m3 x 6mm machine screw, socket head (For TopRail)
• 2x m3 x 8mm machine screw, socket head (For barrel retention)
• 4x m3 x 30mm machine screw, socket head (2x for LowerBrace, 2x optional for RearRail) 
• 4x m3 x 60mm machine screw, socket head (For RearCap and FrontFrame)
• 10x m3 nut 
• 3x 30mm m3 pin (For Trigger pivot, Sear pivot/Grip attachment, and RearCap) (I just bought a length of brass 3mm rod from K&S and cut the needed pins from it)
• 1x 10mm filament pin
• 2x 6x7mm Ball Detents (For Cylinder retention/rotation axis)
• 1x TC length, ~k25 diameter spring (5.5" long for k25, ~5" long for 788. 
  I highly recommend SilverFoxIndustries' SF25-TC springs)

Assembly Guide

Coming Soon

Credits

Sillybutts for some templating for this printables page, and for his rotation mechanism track tutorial

Taffy/Lunko/CharamileDesigns for oring gland dimensions, the Skewer which was an excellent reference for the plunger and sear, and for their general guidance

OrionBlasters for the Lynx plunger oring gland (prior to version 18/06/2025)

Tinkershot for his plunger gland design and for assistance in implementing it (post version 18/06/2025)

My Beta Testers, for all their testing and helping. This project would not have made it without them.

• grey_the_color
• Neat/Kludgeworks
• sidewinder81777
• flibby404

And finally, all the other people who offered advice or simply acted as inspirations for me. Thank you.

Changelog:

18/06/2025: Reworked Plunger seal geometry, adjusted Plunger catch face position, widened Plunger rear, and slightly lengthened Rambase. Overall improves seal and marginally increases draw length.

14/05/2025 (again): Added filament pin to LowerBrace to secure it vertically

14/05/2025: Added LowerBrace to significantly improve durability and fix flex

14/04/2025: Added warning about nozzle size. Added looser dovetail clearance variant of FrontFrame. Made pusher hole in Frame smaller to remove ultra-thin wall 

28/03/2025: Redesigned indexing nub on PumpBlock to improve durability and indexing reliability

27/03/2025: Removed chamfers from RearRail (unneeded with current print orientation) and moved the rail 0.5mm further from the body, to give more clearance for certain stocks

26/03/2025 (again): Added hole to FrontFrame to make removing the detent easier

26/03/2025: Initial Release

NONE of my files are to be used or sold by Frontline Foam, by downloading my files, you agree that you are not Frontline Foam and/or related to Frontline Foam or Derrikk Sun.