This is a second attempt for this question, the first time i put in too many different things that ended up derailing the question.
I'm in the early stages of designing a scifi game and want to use as little handwavium as possible (without ruining the fun). The first part of the game takes place in the asteroid belt and includes handwavium in the form of being able to break down just about anything into individual atoms and using a 3d printers make everything from an ingot to a fighter craft.
Backstory: Your ship was sent in advance to build the infrastructure for our first colony at Proxima b. The follow on ship with the colonists was scheduled to arrive 1 year after you but after 2 years the captain decided to head back and find out what was going on. FTL comms don't exist and the experimental FTL drives that we were used maxes out at 40c (just over 1 month to get to Proxima Centauri and only works in interstellar space so the crew was all in cryo sleep for the trip. When you wake up you find the ship is badly damaged and floating in the asteroid belt.
The intended reaction mass is sabots with a shell of (~11.75% mass) Invar (FeNi 64/36% 8,100kg/m³ specific heat capacity peaks at 545j/kg K at 200C Curie temp of 230C) wrapped around (~88.25% mass) silica harvested from asteroids. Depending on the ship the blocks may be as small as 0.01m³ ~30kg or as large as 1m³ ~3,000kg.
The smallest drone has a single 5m long coil, followed by dual 10/15/20m, quad 20m, and quad 50m for the largest coils. The dual and quad 20m fire 0.1m³ (300kg) slugs, the 50m fires 1m³ (3 000kg) slugs, everything else is 0.01m³ (30kg). The power budget is 56MWh for the smallest, 112MWh for the duals, and 278MWh for the quads. All coils are up to 5m outer diameter. Oh, and these are only used in space so air friction isn't an issue.
So, finally, the question is how do i turn all that into newtons for thrust/deltaV calculations?
Edit: I found Luke Campbell's coilgun equation on several different coilgun questions. http://www.projectrho.com/public_html/rocket/spacegunconvent.php#id--Kinetic_Kill_Weapons--Coil_Guns If i did the math right 398098J is enough to push a 3000kg slug to 1000m/s in a hair over 59 meters. Did i get it right?