Well the first one is where did the dirt come from? Shame, you didn't clean your cylinders before putting them in the gun.
Don't feel bad I've done the same thing and had the same result. If you get the stems resealed at Alan's make sure everything is spotless and try to keep it that way. His seals are harder and can leak easier than the OE ones, I have cleaned the OE's with a good cleaner and a straight pin. Just gently scrape the gunk off and out. His seals will up the fps and shot count for you so.....As for drilling the two holes in the end of the valve, this allows more gas to flow into the valve and will help the velocity, the piercing pin will stay centered even without the hole in the end of the aluminium body so I just make a slot at 90 degrees from the tightening groove to inprove flow. The next step is to reduce the diameter of the head of the valve, do this slowly and don't get it hot, if it feels warm to the touch cool it as you work it down, don't get the area around the seal to thin it can break out. Next if you have a Dremel tool remove material in the brass cap from around the area where the head of the valve sits, open it up and the gas will flow better with less restriction. As to removing material in the port passage in the brass cap, I remove alittle but not much, it's easy to take to much and break through, side to side is better than fore and aft. I have noticed that the machining of the port will almost always leave material on the lft side of the port when looking into the cap from the side inside the valve or to put it another way when looking into the exhaust port the material to be removed is on the right side of the cap. I have a colletion of what not to do to the brass caps in my reject box, one slip of the hand and it's junk. Have fun, be careful.
