On my new flat-top M4 upper, I purchased a ARMS #40 and a GG&G Scout rail to go in front of it (yes, I posted here first, and was assured that this would work.)

Well, it doesn't quite work.  There is a millimeter or two of flat-top rail blocking the forward GG&G screw from fully entering the hole.  So, given that this is the setup I want to run, I'm going to have to take a little bit of the metal off the back of the GG&G rail in order for it to seat a little further back against the ARMS #40.

What is the best way to do this?  I've got both metal files and a dremel tool.  I don't need to take a lot of metal off the back, and I really don't want it to be a sloppy job.  Anyone ever done this before or have some pointers for me?

Thanks!

If you need to take of metal from the back of the GG&G rail I would find a local machine shop or gunsmith and have it trimmed on a milling machine.
Have you tried mounting the rail then the #40?

STS

Yep, I tried mounting the rail first, but that only left the locking bar on the #40 with not enough room to clear the flat-top rail.  I'll have to get a gunsmith to see what he can do for me.  Just shaving a little off the back should do the trick