Lots of questions...
The NERF gun proportions won't work; there is too little room behind the magwell for a proper bolt carrier, unless you are doing a very novel lateral moving block system.
I'm going to adjust proportions and strech the rear a little, but I do have a design that should prevent needing lots of space.
It's nice that you've got a CAD drawing of the exterior, but what does the action look like?
Honestly I'd love to show you, but my legal department does not want me to post any internals because it could create issues when it comes time to patent. Sorry.
I'm curious as the the mechanics of a rear mag release on an AR mag. Last I checked the holes for that are on the side of the mag; you'll need an uneccessarily complex device to accomplish that, or divert from standard GI mags. Oh, then there's the either/or release. Even more complexity. You're asking for critique, you're getting it.
Is that a rear mag release with an AR mag? Have you held a buttstock with that shape - any printed or even wooden mock up - against your shoulder? Definitely not something I want to shoulder, and certainly wouldn't be convenient in body armour. Vents over the breech and wide open sides for ejection ports? Seems great for clearing feed issues, but what happens in an out of battery fire event? What protects the shooter?
Yes, it is a rear mag release on an AR mag. If you want an idea of how it works, it's somewhat similar to how the G3 can use BOTH a paddle AND a button. The internals are not very complex and unlike the F2000 it can take any standard mag, ie USGI, Pmag, Emag, Lancer AWM, etc.
I have held the buttstock in that shape, and I will change it; It's awful without armor and worse with it. First though I need to finish the internals so I can mold the buttpad around that. Another thing I'm going to do that was heavily requested on the F2000 is put a metal shield in the butt so if it blows up it doesn't destroy your face.
As far an the ejection ports go, I haven't finished the design for the bolt or BCG yet, and they're not shown in that image. Rest assured, it will be a closed, locked rotating bolt.
If we're playing make-believe, bullpup style, here's a few thoughts - capitalize upon an abundant supply of AR-15 components. Barrels, bolts, gas systems, etc, as much as possible. A guy would be ahead to make the manual of arms as AR common as possible as well. This gives you access to an already abundant manufacturing base, as well as plays a critical advantage for market appeal. Since you're marketing towards fighting men and women, and not to sportsman, focus on making sure it is body armour compatible - in which case a 30rnd AR mag at the rear can be problematic. Consider these things in your ergonomics.
I remember some of the rifles, handguns, and guns, as well as munitions I designed when I was fresh out of engineering school- I also remember how they all seemed like revolutionary ideas to disrupt an entire market, but then I fast forward to understanding manufacturing and marketing realities... Product development is a dangerous game - it's far too easy for folks to become emotionally invested in THEIR product, such they continue to fish for years and years (and dollars and dollars) when they should have cut bait far sooner. Sometimes it's really, really difficult to accept the reality of having a really great answer to a question not enough people are asking.
The gas system will actually be a carry-over from one of my other products, which is designed to work with standard mil-spec AR parts. The barrel I will probably try to make AR and the pistol grip is already AR.
The dual mag release system is so if someone it already familiar with a bullpup like the AUG, F2000 or the TAR-21, they can do that. Alternatively, if they've used an AK, grabbing the mag and the release is just like grabbing the paddle on the AK, it's just it's behind the trigger. If you're transitioning from an AR or a MTAR / X95, that mag release button will stay the same too.
The 30 rounder at the back was something I WAS worried about, but after testing in a mockup, even a 40 rounder doesn't get in the way, and a 30 rounder is barely noticeable. A Vietnam 20 rounder doesn't even stick out. I may or may not want to change that depending on testing.
This is a product that I am personally excited for. In all honesty, it's hard for any engineer to design something and just give up on it. It's an ego thing. But at the end of the day I realize market demand is what it is, so if this flops, it will end up like the F2000, in rarely-sold-on-gunbroker-for-a-lot land.