AGM M4 A.K.A. money pit
 

I purchased my Agm M4 (WA based gbbr) a couple years ago. It was second hand, from a collector.
First the mag was leaky. Ok, no problem, just buy a new mag.
Evoke sells the king arms gas mag, great! I recieved the mag and it worked ....for a day( 1 fill no leaks) refill the next day....leaks on every o-ring ugh. But let's say at least I got to try out this gbbr, it was awesome!!!!!! Now , I must get this up and running for sure!!! Purchased 4 mags brand new. Ok 3 are good! What evs! Now they don't seat properly . The old mag doesn't either . Maybe the part of the hammer is busted ....I don't know.
Made this gbbr look sweet with magpul furniture, nice eoteck and ambidextrous charging handle.
Well I have a 500 dollar wall hanger ....oh it will shoot .it will shoot

I have the same one. They are good if you like to tinker. Mine works fine with a KA Bolt Carrier and Nozzle. Most of the insides are replaced and it functions ok. The King Arms magazines are known to be of poor reliability. Your valve knocker is probably getting in the way of your mag valve, so I would look there first. My magazine only fits if he charging handle is pulled first. If you want to replace the internals, the parts compatibility is off, so you may need to modify the new parts for fitment.