Quote Originally Posted by JChops View Post
Here's a list I've kept to get you started. I've built uppers with the following versions so these are all confirmed. I don't know if this list is complete but feel free to add if you can confirm something not shown:


MKI 10", 13" (Slick, smallest OD, threaded inserts to attach rails direct)
Version 1: Original design. Steel barrel nut. Heli-coil barrel nut bolt holes. Oversize phillips-head socket cap bolts. Laser engraving along top.
Version 2: Exactly the same as V1 but with QD sockets on both sides.
Version 3 (Current): Bottom vent holes redesigned to pear shape. Steel nut updated to new chamfered design. Anti-rotation "wings" reduced to smaller tabs like MKIV. Bolts updated to lo-pro allen head socket caps and are countersunk into rail like MKIV. Phosphated steel retainer countersunk on opposite side like MKIV. Laser engraving moved near barrel nut like MKIV. Black anodizing has a blue tint to it.

MKII 9.5", 10", 13" (Slick, larger OD, removable keyed backer plates that serve as mounts for rails)
Version 1: Original design. Steel barrel nut. Heli-coil barrel nut bolt holes. Allen socket cap bolts with slight countersink. Laser engraving along top.
Version 2: Exactly the same as V1 but with QD sockets on both sides.
Version 3 (Current): Bottom vent holes redesigned to pear shape. Steel nut updated to new chamfered design. Anti-rotation "wings" reduced to smaller tabs like MKIV. Bolts updated to lo-pro allen head socket caps and are countersunk into rail like MKIV. Phosphated steel retainer flush-mount on opposite side like MKIV. Laser engraving moved near barrel nut like MKIV. (Also, note that the 9.5" rail has replaced the 10" rail.)

MKIV 9.5", 13" (Slick with short fixed rails at 3, 6 and 9 o'clock)
Version 1: Original design. Only current rail with aluminum barrel nut. Small anti-rotation wings. Larger head allen socket cap bolts, countersunk. Phosphated steel retainer flush-mount on opposite side. Laser engraving near barrel nut.
Version 2 (Current): Aluminum nut updated to new chamfered design. Bolts are newer lo-pro allen head socket caps. Vent holes below barrel nut removed.


You could also add the following prototypes and specials that have been shown publicly:

• The "Trident" Rail — 13" MKIV (Sand) rail w/ square bottom vent holes (owned by a member here)
• Citizen Arms Rails — 9.5" & 13" MKII & MKIV rails with HK416 style keyed anti-rotation
• Cola Warrior Rails — (2) 13" MKIV rails (Sand, Grey), with special engraving and HK416 style keyed anti-rotation
• Keymod rail — 9.5" MKIV (in the white) proof of concept shown recently by Bill
MK3 is coming soon. To be honest, I like this one the best of all. I will try and get some pictures posted.