Summary

Ever wanted to setup a Victorian duel between your friends?
How about a pirate boarding battle?
A cosplay prop for your renfaire outfit?
Or just a historical desktop fidget?

Firing Video!
Design Video

Designed after a 'Queen Anne' pistol - popular among pirates, smugglers and gentlemen as they could be made compact and concealable, and unscrewed for easy cleaning.
(There are a host of historical liberties taken in the design - I won't list them all here, but suffice it to say, its hard to design 3d printed Nerf, so I did my best.)

It looks like a black-powder flintlock - but mechanically is more of a Nerf-crossbow!
The mechanism took quite some effort - but I'm pretty happy with the results:

• has a half-cock 'safety' position like a real flintlock
• loading a round automatically puts it into half-cock
• frizzen flung open when fired
• can be made to shoot harder or weaker with different bands/barrel-lengths
• you can peer through the touch-hole to confirm the 'crossbow' is latched
  It will misfire sometimes - but so did the real deal!

No supports and minimal hardware!
Screws:
M3x10mm = 5x(ish)
M3s20mm = 9x(ish)
Elastics:
smaller (like the type used for hair braids) = 3x(ish) - something like these or maybe these
larger (like the type used in offices) = 2x(ish) - something like these
(I say 'ish' here because it depends on your customization options, and there are a few optional screws - you really only need 1 at the tip of the barrel, but could use 2 for extra stability, etc.)
You can choose how many of the larger elastics to use to tailor how hard the pistol fires.
Note that elastics degrade with time and use - so they should be considered somewhat 'consumable' (luckily, they can easily be replaced)
Powder flask requires another 3x m3 screws, primer flask requires another smaller rubber band.

You may also want:

• 'Wadding' can be made from standard tissues (like 'Kleenex') - separated into single ply and cut into small squares
• 'Black powder' can be made from corn starch (I leave mine white, as is - but you can mortar-pestle it with a bit of food-coloring to turn it black, then leave it to dry again)
• A bit of leather (or pleather or scrap cloth) to act as the 'flint cushion'

SAFTEY NOTE:

• Always wear eyewear when playing with this, even if just loading. If the ramrod slips out of your fingers, it will be shot back at your face with considerable force.
• Be careful bringing firearm-shaped objects outdoors - it is unethical to frighten people in that way
• 3d printed rounds are an 'unknown entity' when it comes to how much force they impart (you can use Nerf Darts or Hyper rounds for a more 'tested' impact force)
• If using 'powder' (cornstarch) - best to use outside or in well-ventilated area. Although 'body safe' - no particulate should be consistently inhaled. Luckily, you only need a pinch to get the 'gunsmoke' effect
• Be careful around pets, siblings, etc
• Do not trust the half-cock 'safety' - even in a real flintlock, it was just a 'somewhat safer' state used to load the primer pan before firing. If jostled or unlucky, the pistol can still fire when in half-cock.

A few of different barrel lengths, grip types, and tips are provided for customization! Feel free to remix and add more! All were designed to print on 'normal' FDM print bed sizes - but I did not test them all. If someone could post makes and lmk how the other grips printed, that'd be grand!

Also included for you to print are:

• A powder flask AND primer flask
• Two types of 3d printable bullets (or you can use Nerf Hyper, with some caveats - see below)

For bullets:

• Standard Nerf darts (half and full length) = should work - though wadding may be required - and I am unable to test personally as I don't have any. Same story for .50 foam balls
• Nerf Hyper rounds = work, but I recommend 2ply of 'wadding', The gummy, soft Hyper plastic gets caught without wadding to reduce friction, and 1ply wadding can rip and thus jam.
• 3d printed rounds = actually most reliable and farthest shooting, can be used with or without wadding . However, these are the least safe, as Nerf is designed to be fun for all ages - but 3d printed rounds are not! Only use at your own risk. Always wear eye protection, be very careful when selecting your targets, pay attention to your rubber band strength, etc

I prefer printing the 'smooth' bullet style, with 5% infill and fuzzy-skin. It gives an almost cast-lead look - plus they can be batch-printed.
These can be fired with or without wading, with or without powder, and seem to fly straight enough.
You can assemble the printed, dimpled ball with a bit of superglue, and it may (or may not) have lower barrel friction and fly farther. (I have not tested - feel free to try and let me know!)

Each part can be printed without supports - provided you set the correct orientation. Some are a bit odd: the pan is printed with the powder-surface against the bed, the grip is printed standing up, etc.

Also: The barrels must be printed laying down, not standing up. Don't worry - the barrel does not need support when printing ling down (though your slicer may suggest it). The barrel takes the full force of the shot, and will split along the layer lines if printed standing (thus the slightly odd design with a flattened oval shaped profile - so it prints laying down easily)
(for most printers/slicers/filaments - if you have trouble with overhangs/bridging, pay attention here)

I think this design could be easily adapted for the larger Nerf Rival rounds as well - would people like that? I don't have any, and for my purposes, preferred a smaller final design.
However, if you take a look in the OnShape, you can see the start of that Rival-based design configuration, and I think it could be 'easily' adapted by someone with a bit of CAD skill.

I'm no engineer, and not 'trained' in CAD, just followed youtube and whatnot - so anyone feel free to give it a try!

Here is the box divider used in the pics/video

If you find the elastics fussy to work with - I designed a printable tool for manipulating them

Onshape