Hello DYI, Good to see you're still considering a recoiless
I got use of computer again but for some reason not for today.
So I'm back in library and can't post any sketches from here
I have been day dreaming about a design for coaxial recoiless:
You could have one plate steel cap welded on the 8" pipe and use maybe a cutting of the 8" pipe ( like a very short sleeve)welded on the other plate steel end cap.
That way the end of the pipe and cap could be threaded with several 3/8" bolts for accessing the piston.
The end caps would have holes the diameter as OD of your 4" pipe.
The four inch pipe would be threaded into a piece like a lower case 4" "t"
with a simple blow open piston inside the t. And centered inside the 8" chamber.
I was thinking the rear barrel would be shorter and breech loaded with a plastic and water counter shot, and the front or business end pipe could be fitted with a breech loader sleeve maybe.
I suppose the 8" pipe would rest on the firer's shoulder with a one legged stand or bipod up front. And a wheel (s) attached to the rear tube for transport.
Well, just some stuff to think about
8)
BTW maybe if there is a seperate plate bolted on to the end cap (or side of 8" pipe)the piston could be accesed from there. Or if the piston was made durable enough it wouldn't need to be accessed.
).