When i had designed the PCBs i started making the barrel for the rifle. The distance between coils was dictated by the lenght of the PCBs, which are 40mm long. The coil spacers were going to be 5mm thick, just enough to allow 3mm holes to be drilled accross for the IR LED and photodiode pairs. This meant that coils would be 35mm long.

The barrel itself was going to be a plastic tube again. It could be aluminium, but i would either have to accept significant induction losses or cut a long slit lenghtwise, which didn't sound like an easy task.

V1.0 used a PVC tube with an OD of 10mm and an ID of 8mm, I tried very hard to find a similar tube but made out of teflon, which would reduce friction with the projectiles and improve efficiency. After a long time searching to no avail, i settled for the PVC tube again.

V1.0 barrel:

For reference, this is how the v1.0 barrel looked like before winding the coils. The coil spacers were made out of pine wood, 10x30x30mm. Coils were 50mm long, making each stage 60mm long.

Investigaing arround, i found out that making the spacers out of a ferromagnetic material, would improve the efficiency of the rifle.

From Delta-v engineering: "Flux augmentation is the practice of encasing the coils within some magnetic material in order to reduce the reluctance of the magnetic circuit and improve the magnetic linkage between the projectile and coil. Research suggests that ferrous end caps can give a significant performance boost to low power coils"

So i ditched wood in favour of iron filled epoxy.

I made a couple of silicone molds for 5x30x30mm spacers and i spent the next month casting spacers, at a rate of one or two per day. (i made a 20 coil barrel too just in case)Keeping the spacers square, parallel to each other and consistently spaced was challenging to say the least. I would recommend building a rig to help you if you need any kind of precision.

After casting the 11 spacers needed for a 10 coil rifle, i sanded the faces and drilled through 3mm holes for the IR bridges.

I spaced the spacers slightly more than 40mm to have some clearance between the PCBs. The boards arrived just in time to test the fit, which was as good as i could expect.