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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I have replied to a post on this same subject matter here: http://www.talonairgun.com/forum/viewtopic.php?f=33&t=34864
The way I test for air tube pressure-induced POI change on my rifles (barrel movement) is by mounting a laser onto the barrel/shroud and aligning the dot directly to the crosshairs at my zero distance. I’ve done this to both my Air Arms S410 XTRA and Cricket and the dot has never deviated from its original position across a range of fill pressures.
I will admit that I made this same mistake, blaming the tool rather than the operator. But like in life, it’s the mistakes that which we learn from and try to never make again. And from what we’ve gained from learning we should only pass on good information and advise to help struggling others. With that, I think people need to be careful about pointing a finger to the air tube and making recommendations until it has been determined that it really does influence POI shift through genuine testing methods that actually allow you to “see” the movement, not from assumptions as this is spreading false information and can lead to people making unnecessary modifications (or possibly even damage) to their otherwise perfectly fine rifles.
Cheers!
How can you justify the POI shifting in Cricket – no grub screw there and there were some reports about POI shifting.
Oh. I was misinformed re the 25. Then, the entire family shares the same mid-mounted “float”
The 25 does not have a grub screw. Only has a covering screw.
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sorry guys, If your gun is not shifting POI then why are you writing here.
I believe people who do have POI shifting issues should have a say here
does it make sense? :rofl: