The B.C. DCAR V2 - Standard Darts

The Disk Centered Auto Rotation (DCAR) V2 Muzzle Device for foam dart blasters.

This updated version of my DCAR system features the same dart stabilizing technology with additional configurations and a new mounting system. This new mounting system uses a printed TPU friction sleeve that inserts into the bottom of the DCAR. Compared to the o-rings used in the previous version, this new mount gives more flexibility in barrel insertion lengths as well as being easy to adapt to any barrel size (for example, there is no o-ring size that will work for 17/32" brass barrels).

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 printed TPU friction mount (tested on barrels ranging from 0.620"/15.8mm - .632"/16.05mm) and a plethora of disk and twist configurations:

• Barrel Outer Diameters (OD) - 5/8" (16mm) & 17/32" (COMING SOON)
• Washer Outer Diameters (OD) - 0.312" & 0.280" (more on this below)
• Washer Stack Configurations - 3x3, 3x4, 3x5 & 3x6
• Rifling Twists - 0°, 2°, 4°, 6°, 8°, 10°, 12° & 14°
• Dart Crush - Standard (12.7mm) & Tight (12.4mm)

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, 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, can not print the TPU friction sleeve, 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 the printed TPU friction sleeve for slightly less than sourcing your hardware from a local hardware store.

MODEL NAMING SCHEME

BCDCAR V2 "barrelOD-diskOD-stack-twist Crush"

Example: 0.625-28-5-8 STRD

• barrelOD - in inches, 0.625 is 5/8" barrel and will work with 16mm as well
• 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 - STRD = 12.7mm ; TGHT = 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

The printed TPU friction sleeve can be a little tricky to print; it has a small contact area and not everyone has success printing in TPU. If you can not print TPU, either use the original V1 DCAR (this version uses o-rings) or as noted above you can get a hardware kit from my Etsy shop with the TPU sleeve included.

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 TPU friction being too tight or too loose, changing the scale even ±0.2% can make a big difference.

Happy ACCURATE AND CHEAP Blasting!

CHANGE LOG:

11/11/24 - Added 0° twist options

11/10/24 - Initial Release