First 50 Yard group with Vulcan rifle (tactic)...

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Dude my Vulcan.25 BP does the same thing when I loosen my "Hush" shroud that was designed to replace the factory shroud so the guy I bought the shroud off of sent a o-ring to fit at the base of the shroud so I can have the vent holes lined up on top and the sides and also have the two set screws lined up evenly on the sides because without the o-ring the shroud would thread onto the barrel at an uneven level. this is with the factory shroud and below is a picture of the "Hush"shroud that completely replaces the factory shroud.
 
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Only loosened 1/8 turn from snug. My Colibri does the same thing when the shroud loosens if I shoot a lot between cleanings. And that thing seats around metal, not an o-ring. I come from the camp of barrel harmonics. I do not think enough of a shift at the end is causing clipping. My Colibri end cap was inspected precisely for clipping and nothing.
 
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Very interesting finding, thanks for posting it. The last two high-end PCP I got, I took off the shroud until I was satisfied with their performance. Still testing one of them. I find it hard to determine of the PI change is due to "barrel harmonics" or other "invisible forces", and possibly even clipping, or a misformed shroud/moderator termination that acts like a crown.

In my humble opinion with all the exotic shroud and moderator designs floating out there on factory and aftermarket airguns, the effect on the POI is underestimated and ignored (regardless if it groups properly). I always have an uneasy feeling when I shoot great groups with a naked barrel and then I place the shroud/moderator back on the barrel the POI moves several inches, regardless if the grouping is still fine.

I am not convinced that all the shift in POI is due to barrel harmonics...I suspect that shrouds and moderators do act like an extension of a barrel (thus fps increase possible). Along with their terminations point that acts like a crown of the barrel affecting the pellet's flight (depending how much clearance path is there); And also the internal baffles may act upon the pellets depending on the clearance path again even if they are not touching.
 
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Trapdor: My factory Phase 2 mod is the same way if i don't tighten it all the way down then the holes are on the top, if i tighten it all the way down then they are slightly on the left. But my groups my are better with a loser shroud than tighter one.

TKA87: My Maxi shroud from "Andy" shoots best best with the factory loose but the Maxi shroud tight. He told me don't tighten it down, just "two finger tight"

TKA87, some of my groups shoot that way as well. Then again some 100 yard test can get as small as 2 inches. I've experimented with different rest, different pellets, shroud on and off. Oh by the way with the shroud off didn't yield the best group to date, but only shot that way one session. Very loud with no shroud.

will bring it to the fun shoot this weekend, California.
 
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Pellet testing continues: truth be known i love the MKII's or the idea of them but due to the skirt variations my FPS shifts from pellet to pellet 827 thru 796 very erratic. The MKI's are also nice but get stuck more than not / the magazine does not advance all the time "a lot of mis firers". The Kings have a very constant FPS 906 +|- 4 as far as this Tactic is concerned, not the best groups at distance but getting better.

So after the 8 cans of MKII's are gone :-( I will most like switch to the more constant Kings. The group size with them are improving the more i shot, at first they were an inch at 25 yards now i've got them down to half of an inch.


Ive already shot 1200 MKII's, 600 MKI's, 500 kings, unknown amount of AA, Baracudas, and Polymags (half of each can maybe).
 
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