Posted 02 May 2012 - 09:46 PM
Since this doesn't have a flat answer yet I will try and answer it from what I have found out through research and much digging. I believe there were a total of three rail systems created for the m11. Two were made by maruzen (plastic), they had a limited cqb run edition which had one single rail that was elevated above the bolt. I have never held this rail or seen it in real life. I would guess that this rail is non-detachable but I don't know for sure. The other rail system they made is a fully encapsulating rail system that goes around the entire gun. I have two of these rails. The rails fit almost perfectly around the body of the kwa m11, and at most you may have to do a little bit of dremelling to the rail system. For anyone else that wants to know this rail system will also work around the G&P steel body kit (kit works in kwa m11, voids warrenty probably). From what I have found I believe this rail system has not been made and sold for a few years now, from what I can gaterh online most retailers quit carrying it around 2009(?). The last rail made that I found was produced by G&P. It is (I would guess from pictures) an exact copy of the second rail system described made by maruzen. The difference is that this rail system was made of metal. It came in two versions a black and a "chrome". The last known dates I found for its retail were around 2007(6?).
As for the quality of the maruzen m11 rail system (fully encapsulating), they seem rather sturdy. They tightly hug the gun and provide a relatively quality platform for attachments. If you want to find these rails your best bet would be ebay, or some other site that may sell used airsoft products. Expect to pay for an entire maruzen m11 if you want the rails.
I would assume the fully encapsulating rails were made for the m11 NS1 version by looking at the dates they were discontinued. At least the above rail fit my m11 NS2 version so I would guess rail systems are somewhat interchangable.
There is a chance ehobbyasia will get the maruzen m11 rails in stock; however, I have not seem them come into stock in about a year.