The B.C. DCAR

The Disk Centered Auto Rotation (DCAR) Muzzle Device for foam dart blasters.

Similar to its bearing covered cousin (the BCAR) this muzzle device uses a rolling surface to minimize the FPS reduction while a dart gets twisted through the angled disks to add spin to stabilize a dart. But why use disks (or in this case, washers) over bearings? Three reasons:

1. Reduced cost
2. Local availability
3. A fancy thing called rotational moment of inertia

Bearings are great but they are overkill for a foam dart blaster rifling device. Typical F683zz flanged bearings used in BCARs are rated for 50-100 pounds of force and over 70,000 RPM of rotation. Needless to say, this is way more than we need for foam darts and with this over capacity in load and RPMs comes additional cost and spinning weight. And that leads us in to rotational moment of inertia, or in layman's terms, an object's resistance to changing rotational speed. I am not going to get into the weeds with the math, but what this means is that the higher weight of a bearing will resist rotation more and will suck more energy from the darts velocity. In my testing, a metal washer based DCAR had ~0.8% less FPS drop and a plastic washer DCAR had ~1.2% less FPS drop when compared to the FPS drop from a similar BCAR. While these performance gains are marginal, it is a nice additional benefit in conjunction with the lower hardware cost (around 1/4th the cost compared to bearings)

That's enough theory and math talk, lets make one!

The B.C. DCAR features a triple O-ring friction mount (tested on barrels ranging from 0.620"/15.8mm - .632"/16.05mm) and a plethora of disk and twist configurations:

• Washer Outer Diameters (OD) - 0.312" & 0.280" (more on this below)
• Washer Stack Configurations - 3x3, 3x4, 3x5 & 3x6 (Coming Soon)
• Rifling Twists - 4° (Coming Soon), 6°, 8°, 10° & 12° (Coming Soon)
• Dart Crush - Loose (12.8mm)(Coming Soon), Mid (12.6mm) & Tight (12.4mm)(Coming Soon)

O-RINGS - The B.C. BCAR uses multiple O-rings to create a friction fit mount that covers most 5/8" and 16mm barrels in the hobby. 016 size O-rings are very common in the hobby, if you have made other 3d printed blasters there is a chance you have a few of these laying around! This is the same size O-ring used on the C4 collet grip, SillyButts collet mounting system, and the Lynx blaster barrel mount. If your barrel OD is on the larger side (~16.05mm) removing the middle O-ring will reduce the friction a little bit and make it easier to install.

WASHERS - Typically, washers are a very loose fit on the hardware they are designed for. In order to get a tighter fit, the B.C. DCAR does something very taboo; mixing measurement systems. This DCAR uses imperial #4 washers on metric M3 screws, resulting in less slop and rattle than using M3 sized washers directly. There is currently support for two washer sizes. If you head to your local hardware store and pick up some metal #4 washers, odds are they will be 0.312"ODx0.125"ID (this is the most common #4 washer size in my research). This will work just fine if you want to source your hardware locally, however to maximize the benefit of the light weight washers, you want to use a plastic washer (which may not be available locally). I was able to source black nylon washers online which have a slightly tighter ID fit on M3 screws (these are 0.280"ODx0.120"ID washers). Print the DCAR model closest to the washer OD you have sourced.

SCREWS - The B.C. DCAR uses M3 screws instead of 3mm rods like many BCAR systems use. Most local hardware stores stock M3 button head screws and if you do many DIY printed projects, odds are you have some of these laying around as well. The attachment is designed to use M3x8mm screws, but if needed M3x6mm would also work.

As you can see, self sourcing hardware locally for a DCAR can be done (although admittedly, finding 016 o-rings if you don't have any extra may be hard locally), however these store prices can still be 2-3x more expensive than buying online. The downside to self sourcing online hardware is that (in my research) all these hardware options are sold in bags of 100. Pretty overkill if you only plan on making a couple DCARs.

So, if you can not get the hardware locally, want to use the “perfect” nylon plastic washers I found, don't want to spend a bunch on extra hardware you do not need, or just want to support me and my future product development, you can pick up a hardware kit from my Etsy store! Each kit comes with black-oxide M3 hardware, black nylon “perfect” washers and O-rings (with a couple spares of each) for slightly less than sourcing your hardware from a local hardware store.

Get a hardware kit here!

MODEL NAMING SCHEME

BCDCAR "diskOD-stack-twist Crush"

Example: 28-3x5-8 Mid

• diskOD - in hundredths of an inch, so 28 is 0.280" and 31 is 0.312"
• stack - how the washers are organized
• twist - the angle of the twist
• crush - Loose = 12.8mm ; Mid = 12.6mm ; Tight = 12.4mm 

PRINT SETTINGS

Models have been validated using the following print settings:

• 0.4mm nozzle
• 0.2mm layer height
• 0.5mm adaptive layer line width
• 15% Gyroid infill
• 3 walls/shells
• No supports

Nothing in the model is that picky, so any normal print settings should work fine.

SCALE - Even the best tuned printers can have issues with circles printing undersized. The model is slightly oversized to account for this (0.15mm based on testing on my printer). Once printed, the round base/mount portion should measure 25mm OD. If your scale is a little off, it should not impact the DCAR performance; however if you are having issues with the o-ring friction being too tight or too loose, changing the scale even ±0.2% can make a big difference.

This is my first public released part, so please hit me with your comments or questions!

Happy ACCURATE AND CHEAP Blasting!

CHANGE LOG:

05/11/24 - new configurations (all current planned); minor cosmetic tweaks to all

04/20/24 - Added 3x6 stack configurations

04/02/24 - Initial Release