Hello,

I tried to study some pics but it turned out to be near impossible. So the big question is would ARMS SPR rail fit other rifle lenght forends, too? Like LMT or Troy..? Why bother? Because I'd have two ARs with similar scope mounting height... the other one with SIR and the other one with SPR rail, so I could swap optics without losing zero...and besides quite a few other rail forends look better than the overpriced PRI free float tube.

What if one would just bin the screws, I was under the impression it also attaches to the top picatinny rail of the forend, does it not? Should be rigid enough.

there is some minor, very minor play in the rail to rail interface, that is why the screw.  it will work with KAC FF rail or lat least the older version I had.  

You really don't need the rail. get one of those LaRue mount and it will push the scope forward enough to get your proper eye relief.