Okay, first, I know that it is highly desirable to mount any optic to a flattop receiver.

That said, I have an BM M4 Type with the fixed carry handle. I have a KAC RAS with an Aimpoint Comp M2 mounted to the RAS just forward of the reciever. Per the RAS instructions I have properly torqued the RAS to the barrel nut (20 in/pounds) and I not noticed any significant (if at all) movement of zero with this set-up while shooting.

I should have purchased a flattop but that's water under the bridge. My fixed carry handle upper even has had a KKF A3 TacBrake installed. I have been tossing around the idea of buying an A3 upper from BM but the money I spend on a new upper could buy many other things (ammo, mags,etc, etc...).

I would like opinions from all of you out there on whether you think it would be worth it? Thanks.  

Hell yeah, a flat top upper receiver is less than $100 shipped, I've bought 2 from Pete at Legal Transfer, [email protected]
Whatever work you had done on the barrel you can keep, all that's changed is the receiver, you don't have to remove the FSB or the brake to install it.
I have replaced all of my A1 and A2 uppers with flat tops, and I'll never look back.  I have a mint Colt A2 upper receiver, and all the parts to put together a complete upper with barrel and all that, and I still won't spend the 15 minutes it takes to do it.

Unless you need to mount NV etc the fixed handle and RAS/Aimpoint is a good system.
[img]http://www.forces.gc.ca/dcds/units/jtf2/images/JTF_06.jpg[/img]

Per ARMY FM 3.22.9 which covers the RAS and AIMPOINT it is personal preference as to mount to the receiver or the top rail of the RAS.

You're good to go so long as your happy with it.

It will work fine.  Leave it alone if you are happy with it.

KevinB -- great pic.

Mk1iii -- I can't find a link to the field manual you referenced. Do you know what the name of the FM is?

Like I said, the optic seems to be just fine on the RAS. I guess if the military says it's okay (wink, wink), then it okay for me too.

Still, should have bought the flattop!!!

It's 3-22.9 Advance Marksmanship. Go to Google and it comes right up.

-Mark