Richard, thanks for the work you guys are doing. The testing you did yesterday looks like it was a lot of fun, and you got some good data from it. I'm sure you are getting input from a lot of arm chair quarterbacks, so I'll post my opinion of the video, feel free to take it with a grain of salt, we all know you know what you are doing.
It looks like the prototype works in principle, so now its just a matter of tuning. Based on its operation a lot of the tuning techniques that work for short barrels AR's should apply to this system. With that in mind:
1. A longer barrel and gas system should slow the action down and provide more reliable cycling. I would suggest looking at a MK18 type barrel and gas setup. This system has been well tested and has a lot of data out there. The MK18 system would get you to a barrel length of between 10" and 11.5" with a 6 inch carbine type gas system. With the proper tuning I think a target RPM of 750 RPM is doable. That would make for a very controllable system.
2. The name of the game when tuning a short AR system is gas and buffer. The gas port needs to be tuned in order to get you the right amount of gas and the buffer weight and buffer spring need to be tuned to give you the right BCG return. A tune-able gas system such as the GovNah will give you a lot of flexibility when testing the different gas configurations.
3. Buffer weight and spring - When tuning the gas system, you have to get the right buffer weight and spring tension. With an open bolt system you may need a stiffer buffer spring to give you the forward force you need to properly feed and ignite the primer. When adding a stiffer buffer spring, you may need more gas to operate the system properly.
4. Feed ramps - I'm hoping that the plan is to cut M4 style feed ramps into the upper. With an open bolt system, feeding needs to be clean and as resistance free as possible.
Here's a video of a guy who has done a ton of testing and tuning of short barrel AR systems. He may be able to help with tuning this thing up.
From a magazine perspective I'm hoping that the plan is to match the mag well angle of the AR mag well. A lot of the polymer magazine on the market flare out after the AR mag well, so guns that use straight bottom mag wells that extend below where the AR mag well does cannot accept these types of magazines. I know your not at the point yet of designing the mag well, but just something to keep in mind when you do get there.
Thanks again for all your doing!
