The only difference between a first gen gun and a second gen is the pin size on the reg that protrudes out of the block behind the gauge. A gen 2 reg will not work in a gen one block because the pin is too big. It just plain old won’t fit. The adjustment range on a reg is very small. If you turned the adjustment a little too far in either direction, the reg won’t work. I will tell you that when I had my Krait, the reg or should I say regs were in and out of that gun 5,000 times as I tried to fix them. Once in a while I would experience what you experienced. I knew I had the reg set right but it was in the bypass mode as I filled the gun. Reg gauge just kept following the tank pressure as I filled the gun. I would stop at 160b or so and look at the gun like WTF. I would degass it, take out the reg, scratch my head then put it back in. Sometimes it would be fine when I refilled. If not, I would stop filling at 110b and turn the reg screw a little up, dry fire, then a little down and dry fire. Then it would be fine. Good luck with that gun. I wanted to love mine but at $1,700, it was unlovable. Way better stuff out there in that price range.