WhiskerPCAR v2.0 (Trivictus, RIPPCAR)

This is a low-profile single-piece friction-fitted PCAR muzzle attachment for Nerf hobby grade barrels. Designed to maximize accuracy but with minimized frictional losses with printed rifling. This version 2 is refreshed with new Rotated Intermittent Protrusions (RIPPCAR) geometry for the best possible printable reproducibility and mixed-dart performance at all FPS ranges. This enables Whisker V2 to work with even used community ammo, as well as new darts (even ones with narrower foam diameter from poor Worker QC) across the board. 

(Dubbed the “Whisker” because it's designed to fit through the pump shuttle of the Orion Blasters Lynx, and Lynxes are cats with whiskers at their muzzle ≽^•⩊•^≼)

Instructions:

Simply print. It is designed to be forgiving so any settings work. The only quirk for optimum rifling printing is that you need to use the Seam Painter to draw the seam line on the inside of the bore such that it avoids the rifling lands (see image) to ensure there are no seam burs where the rifling meets the foam. 

Should you need to adjust if it's too tight/loose, use your XY Compensation settings to fine tune the bore size. You should be able to push a dart through with just enough grip to see it spin. It should feel about slightly tighter than pushing it through your regular barrel. For Bambu users, it helps to slow down your wall speed to <90 mm/s. 

For extra QC, there is a set of Rifling Gauge Pins for Whisker v1 in Extras for you to dial in fit. Scale/compensate/tapewrap this pin gauge print until they match your calipers at (12.25mm, 12.30mm, 12.35mm ⌀), then use them as acceptable range reference for measuring the maximum material condition inner bore of your Whiskers rifling. It should barely touch when inserted. Slightly deviating beyond this scale is acceptable, but this is my rough suggestion to give you the best idea for my advised reproducible tolerance. Rule of thumb is that tightbore needs tighter contact, vise versa.

Features & Tips:

• There is another Whisker file titled with “SpigotMXL” in extras; that's designed to act as an optimized rifled spigot for converting your muzzle to fire Mega XL darts.
• Recommend <37cm barrels for Lynxes to avoid collision with the takedown pin pushing the barrel up. Most lynxes are over-barreled.
• I consider porting to be unnecessary, but I've chosen to include it here as you can optionally tape down the holes per user preference
• Whisker is defined around the feature fitting any diameter tolerance of hobby-grade 5/8ths or 16mm barrels thanks to combination of “tension chords” (a line across a circle) and friction bumps that act as crush ribs to secure and maintain concentricity while staying small. This total flexure feature contact region is the best minimal printed method I've found; If you know better, drop me a dm :)
• No PLA FDM tensioning mechanism survives fatigue forever. I like to take off PCARs at the end of each gameday, so they don't cook. That being said, you can lightly torch the tension chords and pinch them inward to refresh any permanent plastic deformation and restore holding potential. I consider these consumables for how cheap they are but it's good to be green.
• Be sure to inspect your bore for any burs; this can happen any time with FDM and can mess up your foam.
• You can shove Whisker into the bore of a Mega barrel to convert that barrel to shoot regular darts.
• There is a pretty Resin version of this courtesy of OutOfDarts. 

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The following is just supplemental thought process to encourage others and inspire ideas, and/or deranged ramblings, whichever suits your vibe 🤗
 

---Theory---

1) Trivictus Geometry

1.1) Three-point contact: 

Trivictus is specifically the name of the 3-land (aka protruding "coils") progressive rifling pattern. 3 is the minimum number of contact points to center constrain a cylinder (dart) down a tube. Any greater than 3, and you add friction that you must tolerance for. Think of it this way: if any amount of "over-engagement" occurs on your lands, the more lands you have the greater the friction is multiplied. The catch is we want to over-engage to guarantee spin, especially on undersized/worn darts. 3 lands happen to absorb frictional tolerances and keep it to a minimum in all scenarios since FDM is messy. (That's not to say you can't have as many lands as you want and have it work, provided you control for consistent conditions.) This is the most widely distributed rifling in the Nerf hobby owing to its adaptability.

1.2) Why progressive aka gain twist?:

Trivictus has a relatively fast twist rate to ensure a very tight flight. Drag stabilization only minimizes yaw and precession, but despite that, all darts are naturally uneven with the leading-edge biasing trajectory as it veers through air over time. By spinning the dart really fast, you average the tip shape that's making contact with the bow wave and smoothing any tip defects or density imbalances that could offset center of pressure. 

Ergo, spinning is not for angular momentum stabilization but to smoothing pathing with surface uniformity. How do we achieve fast spin then? Well, you don't want to have fast twist off the rip, since a high angle of attack will be prone to slippage (slippage causes inconsistent spin and harsher friction). And high twist throughout your rifling creates lots of friction, esp. since you don't need to be spinning that fast early. The progressive part of Trivictus is the best solution compromise to give you the best fps returns while also giving you very tight spin. The pattern is 9°-13°-18°. Within reason, there's no worry for overspin on any muzzle device. Whirlybird patterns that you see on some setups are actually typical of under-engagement low spin and/or unbalanced contact path at exit.

1.3) Tail centering choke:

Trivictus also features a small section of bonus sub-rifling at the end that add to the final stage turning it into a 6-land pattern. This ensures the foam tail remains straight and centered as it exits. 

2) RIP (Rotated Intermittent Protrusions) theory

RIP is a mod to any rifling to further minimize friction while maintaining ensured contact depth against foam to guarantee a clean spin. PCARs struggle greatest with worn/oblong/undersized darts, this is the solution to fix it by mimicking the conditions of a BCAR. 

2.1) “IP” - Bambooing the rifling

(I)ntermittent (P)rotrusions are a lot like "bambooing" your rifling to reduce foam contact and therefore overall friction loss, mimicking bambooed darts. 

Rifling digging into foam is an interference fit you have to balance in design tolerancing. By reducing the overall contact time against the foam down the length of lands, you have greater allowable tolerance to create protrusions that "over engages" into the foam without risking a) sapping too much performance with parasitic friction or worse b) darts get stuck in the muzzle. We can have much deeper lands than what Trivictus allows. And what was originally 60mm of rifling contact is reduced to ~25mm total in the form of segmented stages. Turns out you don't need constant rifling touching of the foam to spin the dart as there is very little energy needed to impart rotation. BCARs were the inspiration for this and proved that you could do it. And rifling protrusions that dig deeper into foam also guarantees we can engage loose foam that would otherwise be too undersized.

2.2) "R" - Get rotated

By (R)otating each stage of our rifling, we ensure that the contact point against the foam is never in the same spot. Foam slightly deflects when it's crushed with rifling engagement, so then any successive contact with that same region of foam will not cut into the foam as effectively. BCARs that had the bearings in line did it right. Each stage of RIPPCAR is rotated out of phase with the previous one to ensure fresh foam contact. The sum total effect is 12 unique points of contact cutting on the totality of the foam shaft. Misshapen/oval darts now have better odds of engagement.
 

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