Being a huge HK and MP5 fan, I personally prefer the early models with the slim line forearm. However, it hasn't been available in Airsoft for ages.
Carrot had a kit but has since discontinued it and I could not find it anywhere.
I've been dying to find a way to get a proper slim line forearm on my MP5 (Not a lover of the Wide Forearm/Navy look) and stumbled across the G&P RAS Kit GP102 and GP103. Upon closer inspection, the G&P kit COMES WITH THE ADAPTER!
http://www.gp-web.com/en/productspop.php?pid=123
http://www.gp-web.com/en/productspop.php?pid=122
I chose the G&P Deluxe since it has that nice barrel that will look much better once the RIS is on. Of course you could just paint your inner barrel flat black as well.
Thanks to HKPRO, I bought a real-steel (Bakelite it would seem) forearm ages ago and have just been hanging on to it for just such an occasion.
The G&P kit was meant for a TM gun, so the ICS MP5A2 (to get the SEF lower) requires some dremmel work and a little re-painting when done. Took me most of the night but now it's complete. The ICS is also full metal unlike the TM ones.
I can now switch between the RAS and the Slim Line at will. However, the wide forearm and taclight forearms will not fit unless you remove the adapter. This takes a few minutes and some tools.
Some notes:
- The ICS body pins are a tad short, the bolt and nut from the RAS kit works perfectly but looks a little out of place. A TM body pin is better (which is what I used). I'll do some hunting for a real-steel one next to make it perfect.
- The G&P deluxe kit includes a nice barrel as well to cover everything up and give even more stability. I recommend it over the basic one.
Here is the finished product: