Tuning Does size matter (moderators)?

[tpw037]

This may be a dumb question so forgive me. Let's just say I have a .30 cal rig setup with a moderator specifically bought with and for the .30 cal. Months later I decide I don't need that much power and get a.177 barrell. I use the same moderator but noticed groups are speratic where they were tight with the .30. I take the moderator off and groups tighten up.

The question is, if a moderator is rated for a caliber bigger than the current setup will it make a difference?

I have my opinion, but it's just that. Anyone have empirical data either way?

 

[Airgunmann]

Seems to me length helps more than width

 

[Airgunmann]

Oops didn't read completely
Sounds like the pellets are clipping from one to the next when swapping guns

 

[steve-l]

Will a larger bore mod work on a smaller caliber gun? Yes, but not with the same level of sound suppression. The major factors that effect sound suppression most is volume and bore size. Optimum bore size for a mod is .040" (1 mm) larger than the pellet diameter.

 

[bucketboy]

^^^ this^^^


Also .30 moderators tend to be enormous in an attempt to quieten things down because they use a lot of air. .177 are much more frugal so don’t need a moderator anywhere near as big to be effective.

Bb

 

[steve-l]

^^^ this^^^


Also .30 moderators tend to be enormous in an attempt to quieten things down because they use a lot of air. .177 are much more frugal so don’t need a moderator anywhere near as big to be effective.

Bb

The issue with all of this if the assessment is subjective. How much is enough suppression to be backyard friendly? One point that I think is very important to all users of moderators is moderator bore to barrel alignment. It is very common to see these things mounted with a skew that can cause clipping. It is the reason most commercially sold moderators have a much larger bore than optimum. It reduces complaints and product returns, but it comes at a cost of optimum performance. The best solution is to detect an alignment issue BEFORE damage occurs. At least the detection of a misalignment case gives the user an opportunity to correct the problem. So then the question is how can this be tested easily. I use an aluminum rod that is at least 2 inches longer than the moderator, turned down for about 2 inches to the barrel land diameter of the gun. These are cheap to make and fast to use simply by placing the rod through the mod into the barrel and observing that the rod exits the mod in the center of the mod bore. If it does not, you have a skew issue. You should own a test rod for every caliper you shoot.

 

[jps2486]

Pellets may not be clipping, but if the hole through the moderator is not perfectly concentric with the barrel bore, then airflow around the pellet as it goes through the moderator is not equal around the projectile, therefore it path will vary.

 

[HogKiller]

This may be a dumb question so forgive me. Let's just say I have a .30 cal rig setup with a moderator specifically bought with and for the .30 cal. Months later I decide I don't need that much power and get a.177 barrell. I use the same moderator but noticed groups are speratic where they were tight with the .30. I take the moderator off and groups tighten up.

The question is, if a moderator is rated for a caliber bigger than the current setup will it make a difference?

I have my opinion, but it's just that. Anyone have empirical data either way?

You haven't said, or I've skipped it, which mod you are using. It could be something as simple as air turbulence. Have you taken it off and see what happens?

 

[dizzums]

yeah, .30 is alittle large for a .177 .. in my experience a mod will act much like an air stripper and actually improve accuracy .. but not if its too large a hole .

 

[Stubbers]

^^^ this^^^


Also .30 moderators tend to be enormous in an attempt to quieten things down because they use a lot of air. .177 are much more frugal so don’t need a moderator anywhere near as big to be effective.

Bb

A larger bore diameter of unused barrel in an efficiently tuned gun dramatically effects the muzzle pressure. In a 30 cal, you have a lot of more volume left to dissipate residual pressure than .177.

Two guns setup in .177 and .30 with 23" barrels where the valve closes at 50% of the barrel length, the .177 cal has only 5.6cc's of barrel volume remaining, while the 30 cal has 14.3 cc's of volume remaining in the barrel.

So it boils down to more than just a generalization that .177's use less air and need less moderator....especially if you're pushing each caliber to its limits or if you're tuning both calibers equally to 12FPE. You can get .177's to shoot 40, 50, heck even 80 fpe if you want, especially if you keep all things equal comparing the two calibers, from ammo weight ratio, regulator setting, ect...

-Matt

 

[tpw037]

Thanks for your replies. First, I want to say that there does not appear to be any clipping on the moderator. It would be strange if my .30 did not clip but a much smaller round did clip. Regardless there seems to be zero indication of that.
My original assumption was that a 30 caliber hole through the moderator is so much bigger than a 177. Is it possible that the air pressure around the 177 upon exiting the barrel caused a lot of turbulence? Does that explain the erratic groups I got?
After putting my .30 rig back together the groups were as I expected. I'm stacking pellet on pellet at 30 yds.
If I were to go to a website to buy a new moderator, typically it asks which caliber I want. That alone leads me to believe that there is an absolute difference between the caliber rating of the moderator versus the caliber of the ammo.
I started this thread to ask if anyone has experienced something like this or at least knows the science behind it (hello moderator manufacturer's or physics majors).
I don't know how else to explain my findings. With the moderator on, the .177 groups are very erratic. If I take the moderator off, the groups tighten up significantly. When I change my rig back to a .30 with the moderator on, my groups are absolutely perfect.
Long and short is, I feel that for one, a 177 doesn't even need a moderator, even for backyard use. Two, if I use a moderator that is specifically for a 30 on a 177 setup, no bueno.
For those interested, I am using a Ronin.
Please keep your theories coming. Maybe we can get to the bottom of this one day. Until then, I'm hanging up my 177 in favor of it's larger cousin (the thwack is so much cooler anyway).

 

[delooper]

While the volume of a moderator matters, the actual internal shape of the moderator matters a lot, as well.

The modern newfangled 3d-printed moderators that have a sponge/tunnel internal geometry -- something that would be near-impossible to machine by hand -- those appear to be very capable.

Regarding group size, as has been mentioned there are a lot of factors that can go into this. Not certain if it has been mentioned but barrel harmonics are also an issue to consider.

 

[Dairyboy]

What gun is this on? Harmonics can cause an issue also.