I am new here so hi everyone. I found this thread due to searching for just exactly what you guys are talking about.
Not sure if I should post here or in a new post, but here goes.
I have been working on such a design for a while now. I realized that the AR platform was limited and I was not happy with those limitations. One being that the lower is milled. And even the most creative have found that you can't really get around that with the design the way it is. The grip position and the fixed magwell position all limit the design.
So I set out to design a new weapon platform that used a 3 part receiver to allow almost unlimited adaptability and customization. (I see you guys already want to do that anyway.)
Following is my own notes on the project:
Concept proposal for new firearm.
The intent of this proposal is to lay out a list of requirements and goals for the design of a new firearm platform that will compete with the venerable AR-15 platform. The concept for this came from the idea that the AR-15 is highly customizable but lacks a few significant capabilities of adaptability.
The platform being proposed will be code-named “Charlie”. (The letter C representing customization) or “CWS” (Custom Weapons System)
The AR-15 platform has a distinct outline that cannot be changed by any significant amount due to certain features of it's design. (a shadow outline of any AR-15 still looks like an AR-15) Therefore, the Charlie system should consider those limitations and attempt to work the design into a manner which can be customized into significantly different outlines to suit personal tastes as well as allow users to own and use the weapon in areas that limit by law weapons which have the AR-15 outline or certain “military” features.
Charlie should be able to be used with a traditional one-piece wooden stock or a two piece wooden stock or with AR style grips and furniture. In order for Charlie to be able to have this wide variety of stock options, the trigger mechanism needs to be nearly at the rear of the receiver. Great examples are the Ruger 10/22 and Mini-14 as well as the 870 shotgun. All can be configured as either traditional or with tactical stocks.
Charlie should incorporate provision for various systems of operation. This would include but not be limited to: Direct gas impingement, over-barrel gas piston, under-barrel gas piston, barrel shrouding gas piston, recoil operation, manual operation, gas delayed blowback, etc. This requires that the upper receiver be designed to allow vast modification.
Charlie should be able to utilize different bolt types and configurations. With various forms of locking systems.
Charlie should be able to except standard AR components as much as is practical. Most specifically barrels, bolts and magazines.
Charlie should be designed from the onset to except standard NATO 5.56x45mm magazines and ammunition. As well as standard AK type 7.62x39mm magazines and ammunition. More types of ammunition and common magazines would follow.
To allow maximum variability of use, the magazine well will be a separate part from the main lower receiver. This will enable Charlie to be set up to use anything from .22lr 10/22 magazines, to .50 caliber BMG. The receiver will be a 3 part design; upper, lower & magwell. The lower receiver should be designed in such a manner as to make the firearm completely dependent on the lower receiver as to ensure no legal issues with the lower being the firearm. This would also allow for the use of different kinds of magazines. Straight, curved, deep well, shallow well, straight insert, rock-in, rotary, spiral, tubular, belt feed, top feed, side feed, etc. To do this the magwell will attach to the lower and the upper will then attach to both. (even though the magwell would be matched to the upper.) So side feed, top feed and belt feed would have a support block in place of the magwell.
Design should avoid using complex milled parts as much as possible. Charlie's design should be such that it can be stamped, milled, formed, cast or bolted; or as many other methods of production as possible.
Charlie needs to be; at least in its basic form, extremely reliable. Using simpler design elements than the AR-15 platform. (See the AR-180) It will be somewhat based on and inspired by the AR-180, Winchester Model 1910, Mannlicher 1901 & Johnson LMG.
Charlie should be produced in its most basic form as an AR & AK competitor.
Charlie's 3-part receiver will be the main design element and this will allow the rest of the market to produce additional parts. Mostly because existing AR parts and accessories will work already.
Due to customizability, Charlie should be able to have right, left, top or bottom eject simply be changing the bolt and upper.
Charlie should be able to be disassembled and reassembled without tools.
Charlie needs to be fully ambidextrous.
Primary points of interest are simplified as follows:
Three piece receiver to enable the system to be adapted and built for a vast range of calibers and magazine styles or types.
Three piece receiver also allows for using many forms or action operation. (Direct impingement, delayed blowback, gas piston, etc.)
Weapon is designed to utilize existing AR type stocks and accessories. (grips, stocks, etc.) As well as traditional styled wood or poly stocks.
Fully maintain without need for tools.(excepting for cleaning rods...which could be stored in the front or rear stock)
Low cost construction adaptable to multiple manufacturing methods.
Three basic sizes of upper using the same lower receiver allows for full power rifle cartridges, intermediate power carbine cartridges or even handgun cartridges by utilizing different length upper receivers allows for large bore rifles as well as pistol and SBR versions.
No dampener sticking out the back.(but an interchangeable rear block would allow a dampener to be used if the user desired it.)
Plan needs to start somewhere, first model rifle will have following features.
Be available chambered for 5.56x45mm and 7.62x39mm.
Be set up with right side eject. But should be reversible.
Be offered in both AR style furniture and classic wood furniture.
The receiver to be made of stamped or formed parts.
Under-barrel gas piston with recoil/return spring in piston sleeve. (the only spring behind the bolt should be a short bump spring.)
Dual rail system for bolt as per an AR-180.
Roller locked bolt, rotating bolt or tilting plate locked bolt. (whichever is easier to make)
Built in telescoping dust cover that slides with bolt.
Ideas for consideration.
Upper receiver should slide onto the lower receiver rather than the pivoting system used for ARs. One or more spring loaded holding pins will hold things together. Take down should be fast, easy and require no tools at all. But when assembled it needs to be solid and secure. Take down can use spring-pins where you push the pin or a lever to take down. But assembly should be just plug together and it automatically snaps back in place. If necessary, use rubber wedges or springs to apply pressure holding things together.
Magazine well should also attach to the lower receiver.
Quick change barrel.
Charging handle to be ambidextrous. Either on the bolt directly, or on gas piston arms as on an M-14.
Bolt needs to be as simple as possible. Roller locked, rotating bolt or tilting-plate locked. (tilting plate is potentially simpler. And stronger.)
Hammer or striker? That is the question. I prefer hammer if possible.
M-14 style trigger blocking safety.
Magwell will have magazine release. Thus allowing for the magwell to be designed for the magazine and not limit that part.
Prototype can be made of a combination of flat plate steel and milled parts. But final design should be able to be made as much out of flat sheet or plate steel as possible. Or at least stamped.
I wrote that about two weeks ago just to get my thoughts down..
Since then I have worked out a large amount of the designs basic details but I have not yet gotten into drawing up plans yet.
I also am including some images that I made (very crude...I only spent about 5 minutes total making these).
I will try modeling something nicer and post some nice renderings.