EasiestPCAR v2 (Trivictus RIPPCAR)

The EasiestPCAR is a PCAR muzzle attachment for Nerf hobby grade barrels that has the best single-piece friction-fit design for a no-frills means to accommodate any standard barrel diameter (16mm, 5/8"ths). Add rifling to any exposed barrel with 40mm of clearance. Comes in 3 aesthetic shapes.

This is an updated v2 refresh of the original EasiestPCAR, now with modernized combined Trivictus and Rotated Intermitted Protrusions (RIPPCAR) geometry concepts. Trivictus is designed to maximize fast twist accuracy but with minimized frictional losses. RIP is there to accommodate undersized darts and guarantee foam-engagement with the land contact to spin even stubborn worn darts, all while conceding even less frictional losses. All tech details can be found on WhiskerPCAR v2  

Instructions:

Just drop and print in any settings. It's the most forgiving print you can ask for. Just be sure to use the Seam Painter tool to draw the seam line away from the from the rifling so no seam burs appear on the point of contact on the foam. See slicer image.

This file comes as a single file for all shape flavors. You can hit the “Split to Objects” button to individualize them. 

Whisker v2's Printables entry has a file set of Gauge Pins (in Extras) that can help you dial in the perfect tolerance for rifling. I recommend printing those and keep tweaking your settings until the diameters match your calipers, then use them to gauge the EasiestPCAR's tolerances. You can deviate from that tolerance, so long as you can feel decent spin with the dart you're intending to use. 

Same rifling as Whisker v2 but uses EasiestPCAR's more flexible tension chord for better reliable repeatable fit on a wider tolerance of barrels.