The darpa coil guns used many smaller bifilar wound pairs to reduce the inductance between the capacitor bank and the coil, they also likely used many parrellel turns instead of a true coil, to increase the amperage while keeping the voltage lower,
due to insulation gap, they likely would have tried to keep the voltages lower as that way you can get more joules closer to the barrel if you can maximize for joules/cubic meter.
They also would have segmented and closed the magnetic path outside of the barrel to focus the magnetic field lines and prevent influence from adjacent coils, like the iron washers many designs seem to use, I assume they would have gone a step furthur and made a 2 part shell to encase the outside of each coil.
Square magnet wire is also likely on the cards, gets a bit lower resistance for the same number of turns however this costs much more for hobbies.
The other trick they likely would have used is different diameters of wire or lengths along the barrel, as the switching period of the coils gets shorter and shorter towards the end of the barrel, meaning you need a lower inductance to peak and dissipate faster.
And maybe the last though i can come up with would be a full cycle push pull as the projectile passes through, as it approaches the opening of the field shell,turn on and begin building up the field, to draw it in faster, it cruises in, then when its approaching the end of the coil you apply a reverse polarity pulse to kick it out while the next coil is drawing it in.