In the spirit of the XM8 (my apologies for continuing the horse thrashing) which is basically a 5.56 mm rifle with a piston gas system. I thought, what could happen if a designer with a lot of money could design a new combat rifle still closely related to the AR design. Except including the only two improvements the XM8 has over the M4.
The gas system and lighter wieght.
So, basing this highly from my knowledge of 3 rifles I own/have owned and shot, the HK SL8, the M1A, and the ZM weapons LR300, I sketched out a sample of what an M4 could become.
Here is what a ZM looks like and it's gas system. Almost there, but still needs a piston, and could stand to lose some wieght.
Here's my sketch. The upper would be able to bolt directly onto an AR15 lower and would not need the recoil buffer and spring.
A polymer lower similar to a CAV arms lower with XM8 influence could be designed and would be very light.
The forend would be polymer and could have an integral rail on top and holes for mounting rails on the sides and bottom, like the SIR. The upper should be easily removable but snap into place very tightly. I would keep the upper aluminum because I think it can handle the barrel heat better.
If you look at the gas system of an M1A or M14 you will see that this system could be very similar, and it would have less parts and be more simple than the XM8(assuming it's the same),SL8,G36.
I would think designing a system like this would be quite simple and very cost effective. Uppers could be designed and replace exsisting uppers and all accessories currently being used for M4s/m16s could be used with this upper. The new polymer lower could then be designed. 3/4 of it has already been made by the CAV arms guys.
I have nothing against HK (in fact I really like them), But I really don't see the point in this XM8 when something better, cheaper, and IMO much better looking could be designed.
BTW, this is all for entertainment purposes. I wish I had the resources to make something like this.
Let's hear your ideas. Maybe we could all design the perfect virtual battlerifle.
I saw some thing like this before. Seriously I saw a m4 development paper that outlined basicly what you are saying. Cost analysis and all.