On my AR buffer tube style P556 receiver The KNS Picatinny adapter mounts up fine but the MCX brace from SB has to ride very high on the gun (orients a few mm above the charging handle slot center line) to keep the collapsing rods clear of the receiver. Some slight grinding down / recontouring of the rods may allow for the brace to mount one slot lower.
Got the Hogue grip and plastic hand guard in and remounted the sliding brace. Two issues: the KNS pic adapter barely covers half of the detent spring (not running a plate back there as the KNS circular male bump was fractions of a mm too big to fit into the hole in the plate) and to get the rods to collapse while clearing the receiver, the brace has to be clamped very high on the adapter. This is going to require me to take the rods to a machine shop to have them re-contoured so that I might be able to go one slot south on the adapter and/or to get an optic with a riser so that I can get a sight picture without the brace pushing my hearing protection off of my ear.
Your brace fits about the same as my stock does ... I've thought about cutting the right stock tube back just enough that I can shoot it with the stock locked in the retracted position but haven't yet.
I need to take a new picture without the bipod as I actually like the regular handguard better than the quad rail.
If you really want something you'll find a way ... ... if you don't you'll find an excuse.
I'm really not a "kid" anymore ... but I haven't grown up yet either
