Sharpshooter Industries Modular Camera Mount System
This is a gun camera mount system from a US entrepreneur from Harrisburg. This is the modern equivalent of the Russian Zenit Fotosnaiper 122 and uses a modified M4 stock and picatinny rail system. MonoRail length:
As a general guideline you want a MonoRail that extends from the front of the lens foot to the front of the camera body. This would be the minimum length. A longer MonoRail will give added versatility by increasing the setup/adjustment range available. It will also provide additional area for attaching accessories such as a strap mount or palm rest or for mounting the system on a tripod/monopod.
How to Carry
You will need to decide on how you want to carry the system, what kind of strap you want to use and how you want to mount the strap. It is NOT recommended to carry heavy setups by a strap attached to the stock. A strap mount hardpoint is a good "permanent" solution as it supports the system by the rail/lens foot. But it can get in the way due to it's fixed placement.