Knight's Armament Co URX 4 Free Float Rail System for M4 / M16 Series Airsoft AEG Rifles (Length: 8.5")

"Absolutely fantastic rail. I was a big skeptical at first because the whole rail screws on to the receiver, but it also has a little bar where the gas tube would normally go that can be pushed into the receiver's gas tube hole and then tightened down with hex wrench from the top. It's extremely sturdy and lightweight. Also, I have a 38mm diameter suppressor inside mine right now and it fits just fine, although I don't think there's enough space inside the rail for keymod attachments. I'd say the absolute maximum size suppressor that would fit inside the rail is around 40mm in diameter.

One con: The rail still needs to be tight in order to hold the outer barrel steady, but mine came with a few small shims/spacers and two larger ones. I needed a spacer that was thinner than the large ones but thicker than all the small ones put together. I ended up having to grind down one of the large ones till it was the right size.

"I got this system for my G&P WOC gas blowback rifle and it actually fit. I really had to work in the threads for an hour or so but no damage came to either the guns threads nor the rail system, it was just a really tight fit. I did use a rubber mallet and a screwdriver but now I can screw it on with my hand with no issues. The rail system looks great, it feels solid, it's stupid simple, and it's just overall a good product. One thing that I guess is noteworthy is that the rail system is about a half millimeter taller than my WOC's upper receiver rail, but it's basically unnoticeable unless you're looking for it. Also if you're looking to integrate a suppressor underneath this system, the diameter is 40mm by 40mm so use a supressor that just a bit smaller in diameter and you should be good to go.

"I got this today and I have to say it's incredible!! It is lightweight, tons of Keymod slots, and you will have a monolithic upper rail with any Madbull M4 receiver.

Pros:
- Knights Armament Co trademarks.
- It DOES accept Mil-Spec and airsoft keymod picatinny segments.
- Exact replica of real steel counterpart.
- Lots and lots of keymod segments.
- Super easy installation (literally screw it on the upper receiver).

Cons:
- It took 30 mins to install because it came with 3 different sets of barrel spacers which you have to decipher what set of spacers works best.
- You will need either a KAC URX torque wrench or a towel and mallet to tighten the upper with the rails.

Summary:
I highly recommend this rail to anyone who wants something more of "your own taste" in accessories placement arrangements. It gives a whole new tactical look to your gun, and its just super awesome!!

"Great rail system. So simple in design it's milsim cool!

This rail is a bit challenging to install and it took 15 minutes to figure out which of the included shims to use to get the rail at the 11 o clock position. Then you can tap it to the 12 o clock position with a rubber mallet, or buy Knights URX wrench. Apply 100 mph tape to the rail system where you strike with mallet if you want to protect finish on the rail.

NOTE: For G&P, KWA and similar threaded upper receivers a MADBULL re-thread tool is required. That will change the thread pitch on those uppers and allow the URX4 to easily thread almost all the way on.

"Fantastic rails, wonderful quality, I got these for a G&P WOC and they do not fit period, I attempted forcing them as another reviewer did but after a full turn I looked at the threads and they were being completely mangled (like I thought they might). Luckily, I stopped before the damage was total and can still use them on my Rec-7.

4 star review because they fit my madbull body perfectly on my Rec-7, no special tools required.

I'll re-review them after trying madbull's barrel thread die.

"Very cool rail. Nice and metal just won’t fit on my G&p body.