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Why I’m a fanatic about index marks

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Bigragu

Bigragu

Member
Jul 8, 2018
4,896
2,390
CA, United States
While shooting today in abnormal winds, I expected totally to see shots either way right or way left if I didn’t guage the wind correctly. 


while shooting just now I noticed my shots are way way low and to the left, the last one totally off the target. Velocities we’re all on board for the first 10 shots, averaging exactly where I had it tuned for-

2D30E7F9-152D-4827-8CD6-0A4073460B22.1651605713.png


so what could be wrong?

one quick check on the index marks on my moderator showed why-

36492909-CF92-499C-954E-DCC0D6EA74F2.1651605952.jpeg

no clipping marks either-

7C808503-2ADB-489B-94EA-C580BB4A2DB8.1651606032.jpeg



back to normal, all is good-

0A30FC0E-04B4-47E6-BD0F-1A8813979BCA.1651606182.jpeg



6DC51606-A762-4FD3-9E22-26089F4F12F1.1651606454.jpeg
2A30B223-51D1-47A2-A128-02AD19EC6710.1651606455.jpeg







 
Unsure, Marc. I’ve had this happen before on my 22 impact. Drove me nuts, as I went from grouping well to garbage. It wasn’t till I was putting everything away that I noticed the Huggett snipe on that, too, had loosened an 1/8 of a turn. So it was after that event that I started placing index marks for quick reference. The silver sharpie on black is easily seen, and easily removed with isopropyl alcohol if need be.
 
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@ Ranchibi-

i own and use vibratite, but after each session I always remove my moderator from the barrel and thread on the 1/2-20 thread protector bushing onto the shroud. Just habit. I don’t like to over tighten a moderator onto the shroud as I don’t want my shroud to accidentally loosen if I go to unthread then moderator and the shroud unthreads instead. I want everything consistent, along with the torque values when it comes to the barrel. From the barrel lock screw, to the liner lock, to the shroud, and then the moderator to the shroud. All has to be the same every time, as I’m not just target shooting but I’m testing modifications, also.

I may head down to my local Ace and pick up a wave washer to help keep it from loosening while shooting
 
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How tight do you normally tighten? Hand tight? I'm dealing with a clipping issue right now and I'm wondering if its a bore axis discrepancy with the moderator, because with the mod off, it shoots lights out.
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I don’t want to say hand tight, but rather “hand snug”.

ive done hand tight in the past and have seen the shroud over tighten onto the liner lock. Hard to describe as everyone has a different meaning for “snug”, lol



I’ve found that with certain pellet/barrel/tune combinations, accuracy can be affected by not only the use of a moderator, but also the type
 
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If the moderator is a 1/8 turn loose but pellets are not clipping- how does it cause the pellets POI to move down and to the left? What’s your theory with how the harmonics were affected?
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Barrel harmonics. If the moderator is not tight it acts like a buffer and changes the harmonics of the whole system. I would GUESS (cause I don't have a freakin' clue) that the moderator being loose would tend to reduce the vibrations at the muzzle but that's worth exactly what you paid for it. I wouldn't expect it to be very predictable in any case.
 
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If the moderator is a 1/8 turn loose but pellets are not clipping- how does it cause the pellets POI to move down and to the left? What’s your theory with how the harmonics were affected?
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This isn't uncommon with normal moderators and I have seen it surmised that air (flash) passing the projectile inside the moderator compresses/bounces off minuscule differences in baffle apertures and "shapes" the flight of the projectile. No proof, only theory. As oldcrow suggests, harmonics could play a role as well.

I have one moderator in the 30 cal range that can be indexed by way of a spring loaded piston to change the POI for different hosts. One host "likes" it at one orientation and it's different for another host.

Whether or not that's actually what's happening I have no idea but orientation seems to matter for some host/moderator combinations.
 
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it would be interesting with the washer idea to pick up about 3 .. tighten it with none, set zero as index marked, then add washers in succession to change the index to see if something in the ldc affects poi .. it probably hangs down some becoming off-center being loose, so theres that ..
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That’s a great suggestion, Dizzums, on the wave washer experiment. I will pick up a few.

After reading your comment on the looseness just from 1/8 of a turn, yes, I checked. Just that little bit and the moderator totally flops up/down and side/side.



on a side note, this loosening of the moderator has never happened before if memory serves me, and the only thing different that I’ve done is tensioned my barrel as explained here-

https://www.airgunnation.com/topic/fx-impact-tensioned-barrel-question/
in combination with my bottle to shroud clamp. 
It’s making me wonder with the inner happenings of an impact the way it’s designed with the hammer slamming up front to open up a valve at the rear, if the forces cause certain parts up front to loosen. I’m my case since my barrel shroud has no where to move to with the clamp and the tension bushing, the moderator is now the “weak link” and is now the one coming loose. With that said, I’m curious if anyone has ever checked the tightness of their barrel shroud against the liner lock after a session of shooting, to see if the shroud has loosened up. 


you know how some folks write in their comments about how baffling it is sometimes, how they put away their fx after a day of shooting, and say it was shooting great only to find out the next day the accuracy went kaput. How many of them have actually checked the shroud or the moderator to see if they loosened up? I’m speaking mainly for the impacts because of its design. 
For all I know I could be speaking out of my arse but it’s very interesting how just 1/8(truly even less than that) of a turn changed my point of impact and consistency all together. 
 
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So I dunno anything about wave washers but I'm wondering if a rubber o-ring or 2 could give you the tension you need to keep your moderator from walking. That's what I use with the protective cap on the threaded barrel of my pistol.

Another potentially helpful hack could be using "ranger bands". They're essentially just heavy duty rubber bands that come in all sorts of sizes. Slide it over the place where the moderator connects, and it can easily be pulled off if adjustments are needed.
 
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So I dunno anything about wave washers but I'm wondering if a rubber o-ring or 2 could give you the tension you need to keep your moderator from walking. That's what I use with the protective cap on the threaded barrel of my pistol.

Another potentially helpful hack could be using "ranger bands". They're essentially just heavy duty rubber bands that come in all sorts of sizes. Slide it over the place where the moderator connects, and it can easily be pulled off if adjustments are needed.
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The only problem with rubber or soft materials between the mating surfaces is they may not provide a consistent "cocentricity" especially as they wear over time.

In the world of normal moderators even wave washers are not ideal. They're great for keeping thread protectors tight but not necessarily the "best" for moderator to bore alignment. Of course this may also depend on whether or not your moderator indexes on the shoulder or the muzzle face.

If you want to keep your moderator from loosening use a mild thread locker.
 
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