Why Vulcan Doesn’t Have POI Problem with Cylinder Fill
Typically, we expect a gun that lacks a free floating barrel to shift its POI as the air cylinder fill level changes. That problem doesn’t happen with the Vulcan, but it isn’t configured as a classical, free floating barrel (barrel supported only at breach block). This was puzzling to me, but I have an idea as to why the Vulcan works. It actually decouples air cylinder expansion from the barrel by having only the center of the barrel hard mounted. The front of the barrel is free. The back end isn’t locked in place with a grub screw. The ends of the barrel don’t get stretched and squeezed as the air cylinder changes fill. Hence, no POI shift with the air cylinder fill state.
Also explains why there isn’t a locking grub screw on the back end of the barrel. If it was locked in place, there would be more issue with POI shift. I think the 25 has a grub screw there, probably due to the higher power output. I wonder if the 25 vs the 22 has more POI shift.
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James you need to lock the nut from one side and turn the bolt on the other side, otherwise the nuts with slots will just keep spinning.
if you stripped the threads on the nuts, no problem, just replace with normal nuts. works just fine
Is the air cylinder supposed to be clamped by the band or floating?
My barrel and trigger assembly (on the band) won’t tighten enough to clamp onto the air cylinder. Also there’s no grub screw holding the barrel so when it’s out the stock the barrel, and trigger ass move about 4mm forward!
Normal
Forward
I don’t own a Vulcan but most reg are design the same way.
Sound like the piston high pressure O-ring (usually the smaller one) is bad, it doesn’t need to be actually leaking just bad/warn-out.
Bad/warn-out, harden from age dried out no lubrication or lack of it can cause longer seat times.
If it does actually leak it will leak out from the reg leak indicator hole, in fact if any one of the reg O-rings leaks it will leak out from it.
Since u’re in there already I’d change them all including the outer ones too.
Also, they’re some cases with Airguns that the hammer/spring/housing needs a bit of cleaning and can be attributed to an inconstant chrony result.
~ Greg
First shot is 25 fps faster. If I shoot a couple more quickly, they are back down. Then if I wait five minutes and shoot one, that shot will be high again. Either the seat or an inner o ring is leaking the higher pressure air into the “regulated” chamber.
First shot is lower then other or leaking ?
Thank you octavius. I just did that yesterday but haven’t had a chance to shoot it afterwards yet. I now find I have a problem with regulator creep on the vulcan as well.
You Welcome 😛
ÄŽakujem. Will file away that tidbit
According Greg advice:
I torque to 20 in/lbs,,,,,,,,,,,,,,,,,, 10,15 then 20.
What torque setting is correct for those bolts?
Did you property tighten screws on block what holds barrel and air tube? Is necessary (is recommended) do it with torque wrench. 😉 Do it with torque wrench and check if you have not tension with air cylinder and stock when stock bolt is tightened.
See example all shooting at 55yards…
https://onedrive.live.com/redir?resid=1ABAD8E7DCE29AD3!161628&authkey=!AJ6gJfDMsmMovYQ&v=3&ithint=photo%2cjpg 20 shots 10 each
I just posted on the yellow, but my cricket rifle and Vulcan 25 DO shift the poi with pressure changes. My air arms s500 and none of my spring guns do. It’s not parallax, the pattern is completely repeatable on both guns, but the pattern is different. The cricket starts high and left, migrates to poa then migrates high and right in a u shape pattern. Every time, same pattern. The Vulcan moves from high and left in a straight line moving down and right. I couldn’t move my head to make that exact pattern with parallax error if I tried. Both guns also have extremely low extreme spreads of around 5-6 fps.
I don’t know why I don’t see this on the air arms, especially since there is a barrel band tight against the shroud. I thought the Vulcan was ok, but when I shoot a bench rest target with one shot per bull, the pattern is clearly there, and again, repeatable. I am baffled as to how to fix it. Shooting the same target with the air arms, the first few shots go the same place the last ones do, 60+ shots later (177 regulated)
I think they also shift poi but the owners stick their heads in the sand
and ignore it
it is the WIND
:rofl:
I think the POI shift is more about the barrel leading up.
kris, I think the original post, from what I’ve gleaned, is not about who is experiencing POI shifts. Rather, it’s about the poster’s thoughts on why the Vulcan doesn’t exhibit any POI shift according to his ideas/findings. Please read it again. I just provided my thoughts and a method on how to actually check for POI shift with respect to the issue.
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Yeah, of coarse mate. I have a tamper proof bit for it to bridge the thread poking through too.