If it turns out it's not an M5 inlet, we have a solution that will work with AICS pattern mags that fits an M5 inlet. Right now short action only, but long action is in development. It's the new Hawkins Precision Hunter DBM bottom metal.
The Hawkins Precision Hunter DBM Bottom Metal is a flush mounted bottom metal designed with an adjustable magazine release. Shop Hawkins Precision AICS pattern magazines online!
I undersyand it isn't a m5 profile but i have made it work multiple times in a bdl stock with some minor dremel work. Was just curious if it might be even less dremel work with a M5 stock. Inket.