Fire Support were as speedy as usual and the G&P adjustable valve stop was delivered today.
TL;DR: 3 easy settings to tune to temps / gas - but may not play nice with stock TM parts, more testing needed.
Overview:
It comes with an o-ring to fit the "firing pin" end of the nozzle spring. Also included is a little grenade pin to help locate the valve stop and align the screw hole.
There are 3 sets of holes for the screw to fit, each a slightly different distance from the front meaning you have a low, medium and high setting as this controls how far back (or forward) the rocket valve sits. Kind of like a 3 step NPAS, but not interfering with the valve function and no chance of unscrewing and firing a grub screw down the barrel!
The brass body has some subtle flats machined into it meaning that it doesn't rotate as you push it down the nozzle to getting the correct hole lined up is easy. The pin makes it easier to locate as it is a snug (but not tight) fit in some nozzles and has to be perfectly straight to seat properly.
Testing:
First I tested my stock TM bolt set up (TM bolt, nozzle, valve, valve spring, Dynamic Precision upgraded nozzle spring set & green piston cup) to get a baseline with 0.30g on ASG gas at 14degC gave an average of 273fps (6fps spread)
I then used that exact set up with the G&P valve stop and it gave the following average FPS: Low - 61, Medium - 152, High - 230.
Yes, those are FEET per second, not meters! Great if you want to run black gas in the middle of a heatwave I guess??? Seems that it didn't play nice with the TM nozzle/valve for what ever reason. One day, when I have time, I will revisit this and try to pin down the issue, I am guessing the internal bore of the TM nozzle is the issue but I can't say for sure at this stage.
I then tested a set up I knew would increase the FPS - Premium Aftermarket Setup (Same TM bolt; Dynamic Precision nozzle, alloy valve, valve spring, upgraded nozzle spring & green piston cup)
Low - 145fps, Medium - 240fps, High - 277fps.
That is more like it! The consistency was also really good, I think from previous testing that this is down to the allow DP valve (3fps spread!). The medium setting will be great for running it in the summer (c. 20degC) or in cooler temps on Red gas. I am guessing the low will be around the 200-210fps mark so probably not that useful unless you have loads of Nuprol Black gas kicking about.
Summary:
A nicely made bit of kit that does exactly what it should and gives enough adjustment for UK weather and gas options. I just need to work out why it hated the TM nozzle, valve and valve spring so much! YMMV.
Pictures:
Blue background - G&P nozzle stop kit, Red background - Dynamic Precision valve