Any plastic air chamber is dangerous don't use it!!!!
First I take no responsibility for what you are about to do.
I used a 1' X 2" aluminum pipe for the air chamber (rear) it needs to be thick enough to with stand 300psi and it needs to be tapped for the gauge, fill button and blow off valve I used a piece of aluminum pipe used for out riggers on a boat.
I threaded the back end and closed it with a black pipe cap (if you could it would be a lot lighter if you could close the end with a aluminum end and wield it. The black pipe cap is the heaviest part on my law.
On the pipe I tapped holes for the gauge, the adjustable blow off valve, and the fill button valve.
The front end of the pipe needs to have a 3/4" threaded hole. I had a friend of a friend do the wielding and I think he wielded a nut into the middle of an aluminum plug to give me a strong threaded end. (Do not try to use the reducers that are designed for aluminum pipe, you can't get them to seal properly).
I used a globe valve (rated 300psi) for the trigger you can get the globe valve, button valve and the adjustable blow off at Grainger and McMaster Carr they are catalogs and are on the web I forget where I got what but if your serious I will search and let you know the part numbers.
You need to use 2"X 3/4" pipe nipples to connect the trigger (globe valve) to the air chamber and the barrel.
To make the barrel I used 2" PVC pipe that is used for under ground electrical wires, it is flared on one end and you need the flare to make a tight seal for the breach loader. (I think I cut some of the flare off I have a 1 1/2" long flare)
My barrel is 19" from end to end. You need to get the pvc fittings to reduce the flare end of the barrel down to a 3/4" threaded hole. (Make sure you check out the reducer fittings, some plumping store clerks will give you more than you need and it will not look good).
Attach the barrel and air chamber to the trigger using the nipples.
I had to cut the lever of the globe valve so it would make it pass the end of the air chamber (don't make it too short it takes a good pull to pull the trigger when it is filled with air).
I tapped a 1/4" hole on the top and towards the front of the air chamber for the gauge.
About 2" back from the gauge hole I tapped another 1/4 " hole for the fill button. (If I were to do it over I would of tapped the fill button hole for a 3/8" fitting it would be stronger). You need brass nipples to attach the fill button and adjustable regulator to the air chamber.
I bought a cheap adjustable low-pressure vertical regulator and 1/4" adapter that you attach the reg to the in put of the fill button.
The reg's intake is off set 90 degrees, I attached a 1/4" adapter to the reg in-take and use a remote to fill the Law air chamber (I use a remote with my marker and because where the reg is attached to the air chamber it is not strong enough to hold an air bottle).
Next to the reg and near the back of the air chamber I tapped a hole for the blow off valve. (Put the blow off valve away from where your head will be).
I drilled a 2" hole with a hole drill about 2 1/2" in front of the flare for the breach loader. I then slid a 2" fernco (it is a rubber sleeve that is used to connect two pipes together you can buy it at any plumbing supply house) over the barrel. This will seal the hole after you load the rocket into the barrel. I also cut a 1/2" off a 2" pvc coupler and glued it to the barrel about 5 1/2" in front of the breach hole so the fernco will not slide off the barrel. You get 2 hose clamps with the fernco slide them over each end of the fernco and tighten them down just enough to prevent the air from escaping out the breach hole but not too tight, you want to be able to slide it forward to load the law.
Now trust me the way I designed this is for safety.
The adjustable blow off is good in the way it releases air, if you fill the air chamber too much, it does not pop, it releases the air slowly (saving air if you fill it to much). Also you may have to adjust it for the field’s specifications. I set the blow off for 275psi and I fill the air chamber to 250psi.
The fill button (rated too 300psi) is used to fill the air chamber when your ready to shoot it, this way you are not running around with the chamber charged, you can charge it when you need it.
The aluminum pipe is light and will not explode like PVC, it will just split if some thing goes wrong.
I used a cheap low-pressure reg (Tippman that I bought on line for about $20.00). I had to take one of the washers out of the reg to get it to adjust properly to 250psi. (The reg adjuster was not sensitive enough).
The most expensive part is the globe valve and the aluminum pipe.
Also don't paint the fernco it will not dry.
If you are serious about this I will take better pics of my Law and post them on the site that I posted above.
With very little practice you can shoot reload and fire again in about 6 seconds.
At 250psi this thing will shoot a nerf over 100' straight at a slight angle it will go a lot further. You also don't need to cut the wings of the nerf.