[mroverkill]

That's just the Magpul PRS stock for G3 receivers. You can purchase a very similar stock for M4 and M16 rifles. Just buy an ICS with the split gear box or any rifle and the Polar star HPA box and you would have a much better performing modular rifle.

 

[mroverkill]

That Magpul stock is already available http://store.magpul.com/prod_detail_list/85 only for real rifles, but as far as I've seen, Marui G3's are compatible with Brazilian RS wood kits, so the stock should be compatible with them as well.