Re-tuning Vulcan 22 for precision and velocity stability
It has been a while since I rechecked my Vulcan’s shooting characteristics. Mine is a 22 that I usually keep at 900 FPS. Its regulator was set to 135 bar using a regulator tester made by John Hagan.
I have been very happy with it, but it’s always fun to squeeze out a little more from our toys.
Here is shot string starting at 200 bar. I started at 200 just to reduced the amount of work. I normally fill to 250 bar and get about 25 shots before reaching 200.
Notice how it comes off regulation at about 135 bar. Also, the segment after regulation climbs. This is due to my hammer spring tension actually requesting a velocity below the max potential of the current regulator/air chamber/transfer port capability. If the regulator were set to match this velocity, around 125-130 bar, the regulated segment would be a bit longer and lack the rise.
I could have simply re-adjusted my regulator. That would have been the end of it. However, remember that the gun’s precision can also be affected by velocity. I also want precision in addition to consistent velocity.
To investigate velocity and precision, I shot groups at several velocities. I made certain the shots were all within my regulated pressure shot count. Because adjusting the hammer spring tension does not immediately take effect with the first shot, I followed the HST adjustments with a single shot to let the HST settle. The single shots were rather haphazardly aimed. Pay attention only to the 10 shot groups. The single shots do however serve as a scale against which to compare the groups.
I noticed that my usual setting, 900 FPS was actually grouping worse than velocities below and above 900 FPS. At max velocity 945 FPS, groups were widening again.
So, to get more precision, I could either decrease or increase my velocity. I wasn’t terribly interested in dropping down below 860 even though grouping was best just below 860.
Somewhere between 912 and 940 the grouping were pretty tight. I also knew from my shot curve, that going up in velocity would better match my current regulator setting.
I decided on 920 FPS to both flatten out my shot string velocity curve and better precision.
10 shot grouping at 920 FPS. Single shot to left. I can live with this.
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I’ve debated dropping the regulator. It really is 135 bar by two separate, independent methods/gauges. Yes, a bit high. Shot count, even when shooting faster, is still beyond my accurate shooting endurance. After 50 or so shots, my concentration and hold definitely degrade. Plus, with a Bauer here, I have unlimited air supply. Extending my shot count out to the 100 range doesn’t matter. I shoot 5 mags when practicing then refill.
I agree, being solely dependent on HST adjustments makes no sense. Equally wrong is using only regulator adjustments. The two balance demand vs supply. I want them in balance at a FPS that achieves the guns precision potential. That might not necessarily match the lowest noise, reduced wear, or longest shot string. I’m also letting the gun determine what FPS it shoots most precisely at rather than arbitrarily deciding.
We’ll retest for best velocity once when permits longer range work. Meanwhile, it is fun shooting paper and seeing the gun repeat so nicely.
If I verify that a FPS is indeed best at full range, then we go back and shoot more shot strings to determine where to set the regulator knee to best achieve that FPS in balance with the HST. Then I will have all working together.
guykuo i see you joined the airgun nation crowd. so messing about your hammer spring?????
:rofl:
if we can trust your gauge… not sure about that i repeat again if your pressure gauge reads correct, you need to lower the regulator to 120bar (135bar is a bit high for a .22)
what that would give is: more used air sitting in your cylinder plus less stress on your guns mechanics. less stress on you if you are pumping it up.
and no off reg spike. you are under the knee so the gun was efficient instead of being consistent across the fill. power output wise. if you turn the hammer in it will cost you shots.
looking at the hst adjustments of the +1,+1/2, 0 turns of the hammer spring and the corresponding speed increments
i think your reg is indeed set too high. because it reacts too good to hst adjustment.
lower the reg a bit and you will find that it will become less susceptible to hammer spring adjustment, should become more consistent for the same reason too.
regarding the balancing act, yes one has to balance the hammer and reg pressure, the volume of the barrel, the volume in the valve and prechamber and the air tube are all communicating vessels, with many variables like springs acting against each other plus changing pressures… it needs to be tuned/worked out experimentally.
you are working around the problem currently, you really have to lower the fecking regulator.
regarding airgunnation, you will learn soon that you have to start praising the sponsors soon, if you dont, you will find it out the hard way soon.
waste of time.
can you check the grouping at 50 yards?
maybe you will like it at 940 fps.
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This is my 12 yard indoor scope calibration target. I use it to set up my Hawke and Night Vision scopes. I also included mag verification scales for setting the Hawke to calibrated power.
The reticle for my night vision is also overlaid on the target. Those are the “tree” with yard markers. This lets me verify my NV reticle is correctly laid out.
When calibrating at such short range, you have to pay attention to very small deviations for the results to be correct at distance. The scope mounting heights have to exacting and I used my own measured BC. It all gets fed into Chairgun and things nicely match up.
Of course the attached is just a jpeg. I print from a PDF that scales just right on my printer.