Best Moderator for Karma SLS compact .25

[Surefire]

Hi Everyone, I am usually an Impulse Air guy for my moderators yet I reached out to Donnyfl about a moderator due to them having a part in designing this airgun. Some-1 got back to me & sent me a link to a Ronin.. I did ask for something shorter/fatter seeing how it's a compact & id like to keep it that way. But I figured that I'd ask this community about they're knowledge on this subject. I like the gun a lot & don't intend to pull the mod on & off a whole lot, rather set it & forget it. I also don't know much or understand why on some of the moderators have a .177/.22 or .22/.25 my IA 1350 that's on my .30 FX Panthera Hunter Compact is a straight .30 & quites the bark down quite well.. I would like something that is designed specifically for .25 only to avoid clipping... I just can't see something that's designed for two different pellet sizes working as good as one that's designed for One projectile size. Also I know that this gun is made in China (now) not usually one to go for such things but if they work & are reliable than well you know.. lol all relevant thoughts & comments are greatly appreciated! Thanks, -SF

 

[subscriber]

You can shoot .177 pellets though a .30 mod and it will work much better than you expect, for two reasons:

Airgun power is roughly proportional to bore area. So, there is no way that a 20 FPE .177 is louder than a 60 FPE .30; when fired through a .30 rated mod. The same principle applies to a .22 fired through .25 mod, or a .25 fired through a .30 mod.

The second reason why, is the predicted loss in performance is incorrectly estimated . This is because the baffle bores represent a small percentage of the overall internal length of a mod. However, with the flat baffle designs such as DFL uses, some air and part of the shock waves can overtake the pellet and leak out ahead of it, even with the correct for caliber mod. Consider that, as the pellet traverses the open spaces between baffles it is as if a .25 mod is baffled for a .75" diameter projectile.

Certainly, if the caliber correct baffle bore ran the full length of the mod, then pellet to tube clearance would matter more. But then, the large OD of the mod would not add functional value. The total volume works precisely because the air is able to expand radially, away from the pellet path. Most of that air slams into the baffle wall, and so cannot leave the baffle bore directly. Ditto for the shock waves reflecting off the baffle wall. The baffle bore area is small compared to the baffle wall area. So, increasing the baffle bore diameter by 1 mm changes the ratio of baffle bore to baffle wall area very little - unless the mod is unusually skinny.

If you shoot a .25 from a .30 moderator that is up to the job for the .30, then unless the .25 is tuned for more power than the .30, or has a very short barrel, the .25 will still be quieter than the .30. The reason to get a dedicated .25 mod is that it will probably be smaller and lighter than the .30. Not because the .30 mod would be louder.

Depending on how your mod attaches to your airgun barrel; directly or via a shroud, making the baffle bores too small may cause just enough clipping to double groups; or may turn your PCP into a shotgun. Worse, would be the occasional wide flier.

There are a small number of very loud folks on the forum that swear that anything over 0.01" radial pellet to baffle bore clearance is a criminal wasting mod performance. There are many more that use one moderator to shoot multiple calibers, that are happy with the sound reduction and grouping ability of their smaller caliber airguns, when fired through a mod intended for 1, 2 or 3 calibers larger than what they are shooting.

 

[Surefire]

You can shoot .177 pellets though a .30 mod and it will work much better than you expect, for two reasons:

Airgun power is roughly proportional to bore area. So, there is no way that a 20 FPE .177 is louder than a 60 FPE .30; when fired through a .30 rated mod. The same principle applies to a .22 fired through .25 mod, or a .25 fired through a .30 mod.

The second reason why, is the predicted loss in performance is incorrectly estimated . This is because the baffle bores represent a small percentage of the overall internal length of a mod. However, with the flat baffle designs such as DFL uses, some air and part of the shock waves can overtake the pellet and leak out ahead of it, even with the correct for caliber mod. Consider that, as the pellet traverses the open spaces between baffles it is as if a .25 mod is baffled for a .75" diameter projectile.

Certainly, if the caliber correct baffle bore ran the full length of the mod, then pellet to tube clearance would matter more. But then, the large OD of the mod would not add functional value. The total volume works precisely because the air is able to expand radially, away from the pellet path. Most of that air slams into the baffle wall, and so cannot leave the baffle bore directly. Ditto for the shock waves reflecting off the baffle wall. The baffle bore area is small compared to the baffle wall area. So, increasing the baffle bore diameter by 1 mm changes the ratio of baffle bore to baffle wall area very little - unless the mod is unusually skinny.

If you shoot a .25 from a .30 moderator that is up to the job for the .30, then unless the .25 is tuned for more power than the .30, or has a very short barrel, the .25 will still be quieter than the .30. The reason to get a dedicated .25 mod is that it will probably be smaller and lighter than the .30. Not because the .30 mod would be louder.

Depending on how your mod attaches to your airgun barrel; directly or via a shroud, making the baffle bores too small may cause just enough clipping to double groups; or may turn your PCP into a shotgun. Worse, would be the occasional wide flier.

There are a small number of very loud folks on the forum that swear that anything over 0.01" radial pellet to baffle bore clearance is a criminal wasting mod performance. There are many more that use one moderator to shoot multiple calibers, that are happy with the sound reduction and grouping ability of their smaller caliber airguns, when fired through a mod intended for 1, 2 or 3 calibers larger than what they are shooting.

Wow Thanks! I didn't even think that there was much to the question I asked. But here I stand enlightened! Not a small task for my longest CK was a 1600+ yarder back in my days in the Marines. (Afghanistan 2001-04). I actually use to have to dump my SSS (sound suppression system) every 30 shots for the internals start to get deformed due to heat. But that was my good ol m4 chambered in my favorite Winchester .308!
-With that
I didn't even think to use my .30 cal Impulse Air mod that I bought for my Panthera.. are you sure that it won't cause some kind of turbulence on a longer shot? Last thing I need is to get that pry in my sights & miss on my famous head shots... (I only go for em) Trained by default I guess). For the barrel is rather short on this compact like 12 inchs.. when I use the impulse 1350 on my 90-100FPE Panthera it does quiet the back down but it still can be heard well, & that's with an additional baffle & switched out screw in to make in flush with it's barrel. I got the Karma compact .25 hitting 60FPE maxed out, with only 2 mags than need a refill.. but I set it back to around 40ish to keep that awesome shot count. In other words what I'm try to ask according to your answer is seeing how I already have the impulse 1350 in 30 cal and now have this new .25 on an even shorter barrel what you said I believe could factor in some issues, for they aren't that much different in power well if tuned my 30 cal down to where I got it from the factory at 65 FPE (yeah going to love those FX ratings of power let me tell you!) am I good to go without worry of any kind of deviations and moa or point of impact? Even full on noise reduction? I mean I haven't tried it yet which I will and I bet it does quiet it down better than factory. But would a dedicated 25 for the 25 be better than me slapping my 30 on there?
I don't mind the $ on another one, for overall performance is Paramount to anything else. As far as these things go for me anyhow I'm sure you want a bunch of guys here I feel the same way! Thank you for your answers plural, looks like I need to try it out myself and I'll let you know my results. But I won't know if there's anything better to go with unless I try it right? For necessity is the mother of all innovation. Thanks man definitely some very great knowledge you have for this! Seriously! I would have never thought about all of that if you didn't chime in. -SureFire.

 

[subscriber]

The Panthera has an active shroud, albeit a short one. The first baffle is either a reflex air stripper feeding the rear of the shroud, or the front cap of the shroud acts as the first air stripper. This is important because the first air stripper is works the hardest to cause a lag in air movement, relative to pellet movement. Either way, the conical baffles of the Impulse Air mods will be more effective in air stripping than the DonnyFL flat baffles. However the metal cones may "ring" and result in a harsher tone than the DFL mod due to its felt lined expansion chambers. So, you are right that you will need to try them out, as I am not sure about the Pantera's factory air stripping arrangement (compared to the Impact, for example).

An important factor that affects how well a given PCP shoots with a given mod is barrel harmonics. It is possible for one mod to improve groups and another to open them, due to the effect on barrel harmonics. That is a function of the weight and length of each mod. Now, the Panthera shroud arrangement looks very stiff, and the internal barrel's unsupported length seems short, so it may be able to tolerate a wide range of mods without noticeable effects on barrel harmonics. If you notice a large difference in grouping ability, or a shift in the point of impact between mods, try tuning the pellet velocity up or down by perhaps 50 FPS and see if that hsa any effect.

All the above assumes that the pellets do not come close to contacting the baffle bores on any mods you want to try out.

As for potential harsh ringing of the Impulse air mod, you can try to wrap the outside diameter with foam rubber or a sleeve that both damps vibration and blocks sound to see if that simple approach improves the sound.

If the Impulse Air mod is loud at 100 FPE, it may simply not have the internal volume to bring the sound down as far as one might like, even with an additional baffle. As internal volume is one of the first order predictors of how quiet any mod will be on a given PCP. Length actually is very important, assuming the mod has enough volume. A simple reason is because you can fit in more baffles in a longer mod. Another is that the air spend more time in the mod before the pellet exits. Baffles that are further apart are more effective at containing sound. If baffles are too close together, air tends to travel straight down the bore, rather than spread out radially - although this is more significant at low power than higher power (and towards the front of the mod), because higher bulk air pressure tends to spread radially into the available space better. Also why conical baffles are more effective than flat ones. Anyway, what I wrote above is just the foreword on a book on the topic, so I am going to quite now

 

[Surefire]

Ok, so I ended up throwing the .30 IA 1350 mod on the .25 SLS compact today. I tried it first with the way it came (baffles wise) than with the extra baffle, than ran it in stubbie (3 baffles). To tell you the truth the sound suppression worked quite well in all of the applications! Let's not forget that I was not using a decibel meter and was in a celler style setup.. I really couldn't tell the more or less baffled shots from one another! Accuracy-wise still great . I really didn't think that using a larger diameter mod on a smaller caliber (.30 on a .25) would have such good results! I may have to get proper decimal meter to see exactly what's going on as far as the drop and sound is concerned. But I definitely did notice a big difference in sound dampening! More so than I thought. But I thank you for you're help, information & input, for I don't think I would have ever tried this if you did not recommend it! I'll have raw info once I have a decent decibel meter to show exactly what the sound definitely is like an all three different stages that I tried as described above. Thanks again, & have a great weekend! -SureFire.

It's members such as yourself that really make this particular forum such a great place. For your input was not judgment, but straight facts that you were willing to share with me out of your genuine knowledge. I really appreciate your time & help. Sincerely -SF

 

[ZekeZX10]

Ok, so I ended up throwing the .30 IA 1350 mod on the .25 SLS compact today. I tried it first with the way it came (baffles wise) than with the extra baffle, than ran it in stubbie (3 baffles). To tell you the truth the sound suppression worked quite well in all of the applications! Let's not forget that I was not using a decibel meter and was in a celler style setup.. I really couldn't tell the more or less baffled shots from one another! Accuracy-wise still great . I really didn't think that using a larger diameter mod on a smaller caliber (.30 on a .25) would have such good results! I may have to get proper decimal meter to see exactly what's going on as far as the drop and sound is concerned. But I definitely did notice a big difference in sound dampening! More so than I thought. But I thank you for you're help, information & input, for I don't think I would have ever tried this if you did not recommend it! I'll have raw info once I have a decent decibel meter to show exactly what the sound definitely is like an all three different stages that I tried as described above. Thanks again, & have a great weekend! -SureFire.

It's members such as yourself that really make this particular forum such a great place. For your input was not judgment, but straight facts that you were willing to share with me out of your genuine knowledge. I really appreciate your time & help. Sincerely -SF

If you wind up getting a decibel meter would be interested in seeing the drop in decibels

 

[Surefire]

If you wind up getting a decibel meter would be interested in seeing the drop in decibels

I actually have one on the way. So results will be posted as soon as I get it.