There are extended risers that let you attach rings to suit you. Back in the day an ARMS #5 rail I think was pretty popular.
Today there are better choices from Precision Reflex used on the first SPR's to John Burns' extended rail.
Found the Burns doodad:
http://wyomingarms.com/product/wyo-lok-optic-riser/The WYO LOK Optic Riser was developed to overcome the shortcomings of the more traditional cantilever optic mounts for the AR-15/ AR-10 style rifles. By utilizing a full length rail clamp and 7 cap screws the design offers improved strength and added versatility when attaching an optic to the AR style rifle or other types using a M1913 Picatinny rail.
•6.375 inch length
•0.500 inch rise
•Machined from 7075 T6 Aluminum Billet
•Type III Hard Coat Anodize
•Lightweight
•7 locking cap screws spaced for optimal mounting versatility
•Patent Pending
•Specifically designed to rigidly lock and align upper to free float tube
•Specifically designed to allow optic to be mounted forward for proper eye relief
•Made in Cody Wyoming USA
•Allows multiple optics to be switched without affecting weapon
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.5" rise in this.
This looks interesting.
