The Mares "Mirage" has been discussed here over a number of years outlining both its advantages and its flaws. The secondary pumping barrel concept, i.e. load the gun via a smaller ID barrel than the one that shots are produced from could be applied afresh in a new gun that avoids the pitfalls of its predecessor.

The main challenge is after placing the main barrel for best airflow, then the accommodation of the pumping barrel needs to be considered in terms of available space and the method of assembly.

One approach would be to have a concentric barrel gun with an oval tank and the pumping barrel on one side, the only difficulties would be can an oval tank withstand 40 Bar plus service pressure and would the gun be unbalanced to a noticeable degree. Another possibility is a hydroformed tank with a bump for the pumping barrel running along it, but sealing and assembly may prove a problem, so the ideas need to be thrashed out.

The main challenge is after placing the main barrel for best airflow, then the accommodation of the pumping barrel needs to be considered in terms of available space and the method of assembly.

One approach would be to have a concentric barrel gun with an oval tank and the pumping barrel on one side, the only difficulties would be can an oval tank withstand 40 Bar plus service pressure and would the gun be unbalanced to a noticeable degree. Another possibility is a hydroformed tank with a bump for the pumping barrel running along it, but sealing and assembly may prove a problem, so the ideas need to be thrashed out.