Finishing my pistol project, as some of you may have seen in the BST forum, I'm going to finally make this pistol run off of 12g's. all I want to be sure of is this, I am ordering parts and I need a small fitting for the ASA to hook straight up to the valve, no macro, one fitting to go into both the ASA and the air port in a classic air valve. All I am doing to make this run off of 12g's is getting a dump chamber or something like that, anything that accepts 12g's and screw it into an ASA that will be right next to the valve.

I am not sure about the length though and want to make sure I get this right, does this seem good?

Also I am worried about how sturdy this will be, I don't want it wobbling around while I'm running and such. That's all I really need. Just need those 2 questions answered and I will be on my way.