I'm a fan of the Springfield Armory Saint Edge PDW. Here's a review and some details on how they put it together; maybe some of it could be inspiration for your project:
https://www.gunsandammo.com/editorial/springfield-saint-edge-pdw-ar-pistol-review/375352
https://www.gunsandammo.com/editorial/springfield-saint-edge-pdw-ar-pistol-review/375352