I really liked the concept of Bluewar's v6 speed loader but could never quite get the rail connecting system from the rail to the body to work well no matter what settings I used.  I revised the connecting system to use printed parts and removed some holes that did not print well and locked up my printer.  All credit goes to Bluewar for the design, I only tweaked it so I could print it on my printer.

Suggested Printed Settings (for MK3S+):

.20mm layer height

20-25% infill

Supports only needed on rail

May need to scale DOWN dovetails/pin by 2-3% depending on your printer

Requires 6x M3x10mm bolts and nuts as original.  

For operation, I found it works best if you get 10 rounds on the rail while keeping it horizontal, use a finger to press the stack of rounds up against the magazine WHILE STILL HORIZONTAL, and then turn it upright and tap on a table a few times.  

EDIT: After dropping the loader, the rail section broke, so I revised it and added fillets to make it stronger.  I also scaled up the pin and bowties by 3%, so you may need to play with the scale on those to make them work in your specific application.