The Primary Arms Classic 21mm Micro Reflex Sight will mount directly to an optic ready P365 without the need for any adapter plates.
Because the P250 does not come optic ready from the factory, the only way you would be able to mount an optic is by having your slide milled, or by using an adapter plate that replaces your rear sight. This particular optic uses the micro RMSc optic footprint. Which means to install it, you would need to use a Leupold Deltapoint Pro adapter plate, or have your slide milled for the Deltapoint Pro footprint. Email us at Techsales@opticplanet.com for further assistance.
The Primary Arms Classic Series Micro Reflex Dot Sight does not include a picatinny mount to directly fit picatinny rails. To mount this optic to your Prism optic, you would need to purchase an RMSc/Deltapoint Pro compatible picatinny mount such as the Leupold Deltapoint Pro Cross Slot Mount, which can be found by using the link below:
https://www.opticsplanet.com/leupold-deltapoint-pro-cross-slot-mount.html
The Primary Arms Classic Series Micro Reflex Dot Sight could be mounted on the M&P FPC if you use a picatinny mounting base that fits the RMSc footprint. The mount at the link below should work.
https://www.opticsplanet.com/sig-sauer-universal-reflex-sight-riser-mounts.html
The Primary Arms Classic Series Micro Reflex Dot Sight will automatically shut off after 12 hours of continuously running. To turn the illumination back on, you will need to press one of the brightness adjustment buttons and the reticle will reappear.
The Primary Arms Classic Series Micro Reflex Dot Sight uses the Shield RMSc footprint and will not be compatible with RMR cut slides. Primary Arms has also released an RMR compatible version of this optic which can be found linked below:
https://www.opticsplanet.com/primary-arms-classic-series-mini-reflex-dot-sight.html