Top Hat Adjustment / Power Wheel and wasting air
I just read the post Adam placed in the Quick Reference section from Tim at Mac1. Tim has found that the typical best tophat setting is 0.1 inch. This is opposite of what we see in the Tophat adjustment sticky which says the factory setting is too high and to start at .07.
I have a stock talon SS .22 cal. I got my chrony a few days ago and have spent much time adjusting the tophat. I have gotten good numbers (about 750 fps at the lower tophat settings) all the way down to a tophat setting of .05 inch. (I did see the phenomenon of POI shift at these smaller gaps when the tophat started to bottom out on the valve).
I did just try the 0.1 inch setting as suggested by Tim from Mac1. This is by far the largest tophat gap I have tried. Here is what I got with my tank filled to 2700 psi. Shooting Benjamin Discovery 14.3 gr.
Power Wheel – fps
2 – 515
3 – 585
4 – 664
5 – 735
6 – 770
7 – 797
8 – 796
9 – 801
As you can see PW setting 7 is the highest I can go with this setup and not start wasting air. And if I can dial down to between 3 and 4 on the PW I could virtually have a micrometer tank. Seems like a nice spread of velocities.
The bottom line is that I believe that with a chrony you can use various tophat settings and combined with the powerwheel find the point where the velocity levels off and you begin to waste air. I have gotten these pellets up to 825 tops in my gun using all types of various settings. I believe that low 800’s is about the tops for these pellets and a 12″ barrel.
As long as your O-Rings are good on your breech, it only takes a fixed amount of air to move a pellet to a certain velocity and whether your tophat is set low or high as long as you can measure where the speed tops out for your particular setup – barrel and pellets – you are probably using the air efficiently. I think that is what Tim is saying in his post, that you can drive yourself crazy trying to find the sweet spot.
The only thing I have not done yet is to count shots using various tophat settings and staying around this same velocity. When I do that I will let you know the results. If I can get the same number of shots before the velocity starts to drop off using a combination of tophat and PW settings then I will have proven my theory.
PS – I am having fun figuring this all out and yes Buzzcat we will share the chrony!
Greg
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By setting the tophat higher the hammer will hit it sooner. It does not necessarily mean that it will drive the valve open further. That depends upon a bunch of variables. The two most important, I believe are the spring force which must be overcome in the valve and the spring driving the hammer into the breech and tophat which is affected by the compression placed upon it by the power wheel, i.e. the PW position.
I am sure that our springs can be slighty different.
When I tuned my valve and put in a 16″ barrel the best set up was PW7 Top hat .70
This is the major question I have… .59 worked with a 12″, .70 worked with a 16″.. then if that’s the case then a simple math constant says that .81 or thereabouts would work with a 24″.
So where’s Tim’s .100 figure into the equation? That’s completely going backwards.
Or is he talking about a pure inch instead of a 10th?
Cripes, I rue the day I bought this gun… Just kidding. 😆
My best set up on my Talon SS with 12″ was PW 3-11 and top hat .59
When I tuned my valve and put in a 16″ barrel the best set up was PW7 Top hat .70
What Tim did is a good standard set up. But for those willing to spend more time over a chrony we can get even more shots using less gas
Thanks Bro, I’ll make it worth your while.
Sent you a PM.
Tophat set at approx .055 – getting 800 fps with PW setting 8
Tophat set at 0.1 – getting 800 fps with PW set at 7
Per my post above the velocity levels off at higher PW settings for both. Therefore I believe I am using the same amount of air for both settings.
Greg
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This is what makes all the airforce guns such….ummmm….er….er…how can i say it…. SUCH A PAIN IN THE ASS. Mine loves .9″ and not less than that. The lower i adjust my tophat the slower my velocities get. Any higher than .9+ then she really waste tons of air. Good thing i measured the top hat clearance before i adjusted it up or down. PHEWW!