This is a thing of necessity, I recently bought a 'spares or repair' Rapidstrike from eBay and noticed an issue prior to stripping it for repair/mod/rebulid.
The magazine doesn't locate particularly well and waggles around in the magwell, it sometimes fouls the pusher, which is goosed according to the seller.
A bit of digging has highlighted that there should be an internal magwell liner - and mine is missing.
A quick question in the Nerf Group turned me towards a couple of options, buy or design.
The 'buy' option would have run me to 16 euros inc delivery, so into Fusion360 I went.
Using standard part images for reference, I drew up the part and then measured a bunch of stuff like the blaster magazine orifice and the magazine its self.
4 hours, 2 test prints later . . . . . . . aaaaaannnnd it's done! :D
Tested on my Rapidstrike with Nerf 6 & 12 dart mags and the Worker 12 dart banana mags - they all fit like a dream.
I'll upload a pic of the fitted item soon . . . .
Prima Select PLA
4 walls for strength, you don't want such a thin part to snap mid battle do you?