Could too large moderator affect POI ?

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aldea6

aldea6

Member
Jan 8, 2018
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Br, Belgium
Hi, today I deciced to shoot my .25 Cricket , in which I put an homemade depinger and Huma regulator, and try a DonnyFl shogun moderator . The groupings at 50 yards were all bad , no matter the pellets I used : JSB King heavy , MKII , Benjamin 25gr …..I changed the mod for a smaller one , the Sumo : same result. I decided to try an even smaller one , the Koi ( which was badly damaged after a shot with the air splitter of my FX being loose , but I was able to fix it) and ...bingo , the Cricket shot pellet on pellet , as a Cricket is supposed to do😉.

So my question : I know that putting a moderator usually shifts the POI , but not necessarily the group , so could a moderator shift the POI if it's too large for the gun , or for the power? Is there more turbulences in large mods ? Maybe some of you had the same experience...

Mike




 
As you, I have always noticed POI shifting with use of moderator, but it has not usually adversely affected accuracy, or group size, at least not to a degree I would describe as "bad". I have read, if slightly out of alignment, the pellet can pass extremely close to a baffle, without clipping, and suffer a loss of accuracy. I guess this would be due to some turbulence in air flow. I have not experienced this, and I'm not sure it's true. 
 
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Yes, I've already heard about this problem of pellets not going perfectly centered through the baffles. Could be possible, but difficult to check.

@STO : on the Cricket , there is a cap at the end of the shroud , which fits very snugly and is epoxy glued. I removed it and turned another part on my lathe which acts as a new cap on one end and is threaded 1/2 UNF on the other end , on which the moderator is screwed. I checked the part to be centered with the shroud , on my lathe with a dial.

The fact is that the gun shoots much better with the smaller mod (DonnyFl Koi) than with larger ones ( Sumo).
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Be it clipping, turbulence (a Diabolo will self stabilize)
or weight. Anything can have an effect on harmonics thus changing your POA/POI previous zero.

I like the carbon fiber lightweight LDC’s as I don’t need a super robust build & blast baffle. 
Airguns are finicky. My last buy, a Rocker1 on Sumatra .25. Awesome quality and amazing at doing its job. It changed POI from drilling holes to dang. I placed a polyurethane 1/8” thick washer between it and end of threads on muzzle. Corrected my zero and back to drilling holes.

Sometimes you gotta play. A harmonic balancer (thick tight piece of hard rubber) placed midway from stock & muzzle, up & down can change everything. Opening up the aligned passage.

I have a real BSA hammer forged barrel on my Ultra/Scorpion hybrid.177. That barrel is so not concentrically bored it’s obvious without measuring. It took some fiddling but, lights out again quietly.

I took a end cap from an old Gen 1 Marauder from one of 8-10 I had and put it on new Gen 2 .22 as I noticed new end cap on .22 was quite large. It got quieter and shot just as good as bigger hole. You never know for sure beyond basic idea of system. Some “tuning/fiddling may be required.
 
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It looks like the Cricket has a floating type of barrel inside of a long shroud? It could be that the larger moderators are weighing down the barrel, causing a slight droop, and that has effected harmonics enough to make the group size larger. Could you measure or at the least be able to see the difference between the gap at the air tank with each installed?
 
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It looks like the Cricket has a floating type of barrel inside of a long shroud? It could be that the larger moderators are weighing down the barrel, causing a slight droop, and that has effected harmonics enough to make the group size larger. Could you measure or at the least be able to see the difference between the gap at the air tank with each installed?
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^What this gentleman said is what I'm getting at. It doesn't matter how perfectly your threaded mount is centered in your shroud, if you put weight on that shroud and can move the shroud relative to the muzzle of the barrel, adding weight will push them out of concentricity. 

It is the most obvious explanation as to why a heavier moderator would cause clipping while a lighter one would not, all else being equal. 


This is easy enough to test by the way. For safety degas and unload the gun, then put a camera in front of the muzzle (so as to avoid putting your head in front of the end of the barrel) and a bright light at the open breech. Line the camera up so that you can see down the barrel perfectly. Then flex the shroud, simulating adding weight to it. If you see the shroud move relative to the barrel, you have your answer. 
 
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It happened with my taipan 22..it don't like sumo or the shogun ..but it shoot perfect at any distance with the koy .25.....and my .25 taipan shoots awesome with the shogun..in .25...but for shooting bullets with the condors I run the .223 with a .22 sumo..and the 257 with a. 25 sumo ..they work perfect striping the air from the bullet..no clipping...I think that for pellets I will always go one size up..
 
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Everyone talks about harmonics. Anytime you attach something to.any barrel you are changing the harmonics. But i have never had an issue. 

Too big as in od or are you referencing the ID of the baffles? As mentioned clipping or near clipping can.cause an issue. Many can can be rotated to possible rid the problem. 

Cans can also be used as a tuning device if it is a slip on on spring and pcp. I like a slightly.larger ID than.the caliber. This aids in clipping issues and any close passes if all is centered. Remember most bores are not truly centered. A bad off centered Bore ID Can baffle strike. Double loading on guns that are capable of so are baffle nightmares. Even with a clip usually the disturbed baffle can cause issues. 

As to large of an ID you end up with more noise. The bigger the OD you can make for a quiter gun. 

Now a bigger heavier depending on the gun, barrel OD and more you can get some barrel droop and a noise heavy gun. 

I've gotten away with several all metal can designs on a floating 16mm guns. I am not disagreeable on any harmonic affects. But have not had any that did not not make accurate shooters. That goes to the extent of using Sch 10 ss full sleeves not shrouds. 

As always when I am over here its only my opinion. 

Thanks AGN for allowing me on your forum.,💀
 
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bucketboy said:
Stick a piece of tape over the exit hole of the mod, take a shot an see if the hole the tape aligns with the mod



Bb
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Hello, can you explain this option better? I don't understand. But my cricket 2 tactical 5.5mm DOES NOT group WITH the moderator (shroud) and WITHOUT the moderator (shroud) groups very well at 50 meters. Thank you.
 
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