This is the procedure I used to accomplish the task.
The reason I did this is so that I could use an inline reg.
I used the benchmark VA with the collar. I purchased it from www.actionvillage.com
It is not to difficult to do. You will need a few tools. The standard stuff like wrenches and such for disassembly. But more importantly you will need an 1/8"-27 pipe tap. You should be able to find them at most hardware stores or Sears stores.
You will also need to change your asa, the stock asa/reg threading is metric and will not accept a new 1/8" fitting. You will most likely have to get rid of your stock drop forward because of the offset hole pattern unless you find an asa with offset holes or you re tap the stock drop.
Dead On makes Asa drop forwards with offset holes.
Alright to get down to it.
Difficulty scale:6 (1-10 10 being most difficult)
Read all instructions first!
Warning! The body of the 4.0 like most other markers is made of aluminum. It is a soft metal, be sure you take care in what you are doing. Any mistake will most likely be a lasting one.
Remove the asa/reg, bottom line, fore grip/x chamber and set them aside. Remove the trigger frame, entire valve assembly including the valve, and bolt with hammer. Basically disassemble the entire marker.
What you will have left is the body with vertical feed tube and the threaded stud with gas tube where you had the fore grip. Remove the mounting stud with a wrench if it does not come off with moderate force heat it with a hairdryer for a few min on high.
Now that you have that off. Take a nylon bristle brush or a stiff tooth brush and clean the threads in the body to which the stud was mounted. Now run the new VA in the hole till it is FINGER tight. Most likely it will not thread all the way in. This is where the tap comes into play.
You will need to tap the hole a little deeper to get the VA to thread in all the way to the collar. Run the tap into the hole, you will encounter resistance after the tap is in a few turns. When you get to that point use a wrench and turn it in 1 to 1-1/2 turns BACKING it out a 1/4 turn for every half turn you make. That will break off any chips that accumulate during the thread cutting process.
Next remove the tap, brush out the hole and run the VA back in to check your progress.
Continue this process until you get the desired effect.
Being able to thread the VA into the body and when the collar of the VA begins to reach the bottom of the body it begins to tighten up and you will need to tighten the last turn or so with a wrench. BE SURE the VA DOES NOT thread so far into the body that it enters the valve housing. If you use the collar it should not. Be sure that after you are done with the tapping process there are no sharp edges in the valve housing, that might damage your valve o-rings during re-installation of your valve. If any burrs are present they must be removed carefully with a small jewelers file, x-acto knife, or deburring tool, being careful not to damage the valve housing.
Clean both the threads on the VA and the threads in the body with acetone (nail polish remover) That ensures a clean surface. Apply Medium strength Loctite (Blue removable strength) to the male threads of the VA. (be sure to shake the Loctite prior to use) Now thread it into the body and tighten with a wrench so it is seated in it's finished position, and set it upright so no Loctite enters the valve chamber. Allow to cure for 12 hours before you gas it up and set for 1 hour before you mess with it to continue assembly.
Disregard if using a trigger frame other than the stock frame.
The trigger frame will interfere with the VA when you try to put it back on. So you will need to round out the front portion of the Frame so that it does not interfere with the VA. I use a Dremel with the small drum sander attachment, and sanded a crescent shape out of the front of the frame. But just enough for it to clear the VA. I painted the freshly sanded frame with emblem re finisher(if you know someone in the service it is called M-NU) but a matte black paint will work just fine.
Reassemble your marker using new fittings and/or gas lines and asa. Gas it up check for leaks with soapy water and you are all set.
This is what mine looks like when finished.