The
Shield SMSC micro red dot is the recommended sight it will co-witness with the HellCat's sights the
Springfield Armory Store is out of them I am waiting for them to come back in stock & are one hundred bucks cheaper from Springfield Armory compared to optics planet
Shield SMSC it mounts directly to the cutout on the Hell Cat with two small screws and has a 1° shim plate if needed. No mounting plate is needed for the Hellcat Most of these red dots their base is too tall the
Shield SMSC micro is much thinner at the base. The
Shield SMSC features a 4 M.O.A. dot and a light yet sturdy polymer body, the
Shield SMSC mini-sight compact is ideal for compact carry guns such as the Hellcat™ OSP™. The optic is powered by a single CR2032 battery and sports a quartz-coated polymer lens for clarity and shock-resistant durability. Comes standard with battery, mounting screws, hex wrench tools, sight adjustment mini dial, and 1° shim plate. It looks like they are back in stock I have just placed my order for one 299 and saved 100 bucks compared to Optic Planet price of 399.
https://store.springfield-armory.com/Shop/pc/Shield-SMSc-Micro-Red-Dot-4-M-O-A-292p1954.htm
https://www.opticsplanet.com/shield-sights-reflex-mini-sight.html