point defence turrets

Your turret can basically only ever go 180 degrees, assuming everything is perfect and the turret is extruded.

I don't have access to my PC to see the design, but you rarely ever need more than 360 degrees per second, so go light if you can and still keep a somewhat high speed. if you have less firing arc, go slower and lighter, or maybe even an actuator if it's cheap and light enough.

As for the loader, you only need to shoot enough to hit the thing. Making a singularity out of the loader usually isn't necessary.

Several points:

• Do post module editor screenshot(s) - this will allow people to take a look without importing the design into CDE and running the game.
  
• IMO there is little point making EM (rail- and coil-) guns below 3-4km/s. In this case you could get similar performance out of 0.5kg conventional turret taking several W (instead of 200kW) and fitting comfortably in your pocket. I think the only worthwhile potential reason for making low velocity CG is CGs tending towards long, needle-like projectiles which may improve penetration, especially at low velocities.
  
• Lead makes poor momentum wheel material because, while dense, it is very weak. Osmium is usually the go-to material for momentum wheels because it's both the densest non-exotic material in existence and very strong. Reaction wheel mass can be minimized by minimizing excess diameter of the turret over the barrel - of course some tradeoff might be necessary here, but try to make the lightest wheels and make them spin as fast as possible within your power envelope first as a rule. 
  
• For low power applications actuators perform much better than momentum wheels. Alnico offers good performance, but neodymium-iron-boron allows for the most compact ones and is usually the best (if expensive) magnet material for that. Anything below 1MW is usually a low power application. You could
  
• Hafnia is expensive but allows for the most compact, and thus lightest capacitors AFAIK.
• Your autoloader is overkill. With this weapon you could drop to as low as 1W without impacting performance. The practical rate of fire is capped at 33.3ms for engine reasons (there is rarely need to consider anything more except for quirky stuff like capacitorless gun staggering and purposeful thermal throttling) and if you have extra power to run loader and capacitor in parallel then reload time doesn't need to be shorter than charge time.
  
• Your barrel armour is overkill. With exit velocity this low this kind of accuracy is probably wasted - you won't be shooting ants, and at ranges where it would be useful to hit anything larger the target will have moved significantly before impact. Also, amorphous carbon or diamond would work better here.
  
• Your turret armour is weak. It's unlikely to be hit directly by kinetics, but it needs better flash and laser protection.
  
• Except for highly specific use cases you should probably always use magnetic metal glass for CG armature. It's painfully expensive but performs so much better.
  
• Considering hints above, even when sticking with coilgun, you could make the turret alone fit in the palm of your hand, track even faster, and reach 2km/s (without substantial tweaks to the coil apart from replacing it with VCS to withstand stresses of firing), with most mass, apart from the magazine, taken up by large-ish hafnia capacitor (putting the whole gun without ammo at slightly above 2kg). At this point you should probably detach the magazine even if it's not explosive and especially if it's filled with long, needle-like projectiles, because of how bulky it is.
  

thank you all !

Have you tried a similar size rail without the capacitor? I think it might actually work out a bit better in terms of fire rate and cost of the thing itself.