Make sure the angle of engagement (AoE) on the first tooth of the sector gear and first tooth of the piston is spot on. You can search around for more information if you're not sure what all that means, there's a lot out there on AoE. Second, make sure your gears are shimmed very well as well as adjust for proper motor height. Lastly as well as optional, a MOSFET. Realistically you don't need anything fancy, just something to keep your trigger contacts from arcing.
None of that information is new, and there is A LOT more out there and in more detail if you need help.