Some time ago we did a test on a full range of centrefire moderators to determine once and for all what was quiet, light, short, fat, thin, expensive, cheap, best for recoil ...etc etc
Same rifle, same ammo, same day. same sound meter....
Rank everything.
Here: Reviews and Tests – Edinburgh Rifles
During the test I took the opportunity to test and more importantly measure the impact of radial clearance on sound attenuation.
We ran the following out of spec calibre/bore combinations
.243/6mm through the .22 rated baffle - bore of 6mm - radial clearance 0.165
.25 through a .22 rated baffle - bore of 6.8mm - radial clearance 0.13mm
.270 through a 6.5mm rated baffle - bore of 7.45 - radial clearance 0.205
It was no surprise to me that the three highest sound attenuation figures were those that had the lowest radial clearance
Reducing the radial clearance around the bullet has a much more significant impact on performance than considering all other design criteria and material choices.
There is no free lunch however. There is a reason they are not made this way.....lawyers mostly...
Running tolerances this close requires a very accurate, bore concentric thread on both moderator and muzzle to avoid the likelihood of baffle strike and moderator destruction.
I know....we have blown a few baffles in testing....
Any change in torque on the moderator that would allow for the moderator to loosen would present a prolem in this scenario as the bore would be misaligned enough to cause the bullet to contact.
This is not the case with a decent factory or custom thread and a normal radial clearance of 0.5mm
Having worked with a number of moderator brands I personally settled on Freyr& Devik and have tested all the models finally settling on the FW149 for my own personal .308 (Tikka T3 Varmint)
Its the lightest, shortest, slimmest and despite not being produced at the time of our test, performs very well against the market leaders with a sound attenuation of between 27-29dB
The .30cal model has a standard bore of 9.1mm (enough to allow the neck of a fired .308 case into the muzzle)
I have recently had a 6.5 rated FW149 bored out to 8mm
.308 bullet is actually 7.82mm - radial clearance of 0.09mm...or 3-4 thou in old money....give or take a smidge
Testing a bullet in the muzzle of the moderator it has room to wiggle but only a very small amount obviously.
Fitting to the rifle and viewing the muzzle from the breech end for any shadow didn't indicate any issues with alignment.
The F&D threaded sections are very well made
The Tikka factory thread also.
On testing (this time without the benefit of £10k worth of Brüel & Kjær 2250-S sound analyser...) I wanted to see
a) if it would shoot without clipping
b) if it would shoot accurately...and where
c) just perceived sound attenuation and any difference in report.
Target set at 100m
One shot fired through the 30 cal FW149
Moderator swapped over and the "Custom .30cal FW149 fitted - two more shots fired.
Ammunition used was 136gr Peregrine VRG4 - (Home loads, 44gr N133 pushing 2900fps)
Accuracy/POI
First shot (30cal FW196) - on the paper
Second shot (custom .30cal FW196) - same hole
Third shot (custom .30cal FW196) - same hole
a L shaped 1.2cm ragged hole indicating no shift in POI
Sound Attenuation
The original moderator is good but there is still a noticeable boom to it.
I have shot it without ear defenders and even with several shots in quick succession it is not unpleasant, no major ringing of ears afterwards.
The new moderator has noticeably less blast/boom/low frequency noise to the report, supersonic crack is still there, but the signature is much less intrusive.
Now the physical part is proved I need to get some real world data on increased sound attenuation
Will be doing a direct comparison of unmoderated/moderated/super moderated Muzzle Velocities for my own peace of mind too.
Having read studies of increased MVs with mods I am intrigued to see if the expected higher pressures in the tighter bore mod actually increase MVs
Pics for clicks
1) Standard 30cal FW149 with fired 308 case in bore, fits but snug
2) Comparison of bore i)Front- 8mm bore, ii) Rear standard 30cal bore
3) Three shot group from two moderators with different bores
4) Peregrine VRG4 - very pretty bullets!
more testing to come
Same rifle, same ammo, same day. same sound meter....
Rank everything.
Here: Reviews and Tests – Edinburgh Rifles
During the test I took the opportunity to test and more importantly measure the impact of radial clearance on sound attenuation.
We ran the following out of spec calibre/bore combinations
.243/6mm through the .22 rated baffle - bore of 6mm - radial clearance 0.165
.25 through a .22 rated baffle - bore of 6.8mm - radial clearance 0.13mm
.270 through a 6.5mm rated baffle - bore of 7.45 - radial clearance 0.205
It was no surprise to me that the three highest sound attenuation figures were those that had the lowest radial clearance
Reducing the radial clearance around the bullet has a much more significant impact on performance than considering all other design criteria and material choices.
There is no free lunch however. There is a reason they are not made this way.....lawyers mostly...
Running tolerances this close requires a very accurate, bore concentric thread on both moderator and muzzle to avoid the likelihood of baffle strike and moderator destruction.
I know....we have blown a few baffles in testing....
Any change in torque on the moderator that would allow for the moderator to loosen would present a prolem in this scenario as the bore would be misaligned enough to cause the bullet to contact.
This is not the case with a decent factory or custom thread and a normal radial clearance of 0.5mm
Having worked with a number of moderator brands I personally settled on Freyr& Devik and have tested all the models finally settling on the FW149 for my own personal .308 (Tikka T3 Varmint)
Its the lightest, shortest, slimmest and despite not being produced at the time of our test, performs very well against the market leaders with a sound attenuation of between 27-29dB
The .30cal model has a standard bore of 9.1mm (enough to allow the neck of a fired .308 case into the muzzle)
I have recently had a 6.5 rated FW149 bored out to 8mm
.308 bullet is actually 7.82mm - radial clearance of 0.09mm...or 3-4 thou in old money....give or take a smidge
Testing a bullet in the muzzle of the moderator it has room to wiggle but only a very small amount obviously.
Fitting to the rifle and viewing the muzzle from the breech end for any shadow didn't indicate any issues with alignment.
The F&D threaded sections are very well made
The Tikka factory thread also.
On testing (this time without the benefit of £10k worth of Brüel & Kjær 2250-S sound analyser...) I wanted to see
a) if it would shoot without clipping
b) if it would shoot accurately...and where
c) just perceived sound attenuation and any difference in report.
Target set at 100m
One shot fired through the 30 cal FW149
Moderator swapped over and the "Custom .30cal FW149 fitted - two more shots fired.
Ammunition used was 136gr Peregrine VRG4 - (Home loads, 44gr N133 pushing 2900fps)
Accuracy/POI
First shot (30cal FW196) - on the paper
Second shot (custom .30cal FW196) - same hole
Third shot (custom .30cal FW196) - same hole
a L shaped 1.2cm ragged hole indicating no shift in POI
Sound Attenuation
The original moderator is good but there is still a noticeable boom to it.
I have shot it without ear defenders and even with several shots in quick succession it is not unpleasant, no major ringing of ears afterwards.
The new moderator has noticeably less blast/boom/low frequency noise to the report, supersonic crack is still there, but the signature is much less intrusive.
Now the physical part is proved I need to get some real world data on increased sound attenuation
Will be doing a direct comparison of unmoderated/moderated/super moderated Muzzle Velocities for my own peace of mind too.
Having read studies of increased MVs with mods I am intrigued to see if the expected higher pressures in the tighter bore mod actually increase MVs
Pics for clicks
1) Standard 30cal FW149 with fired 308 case in bore, fits but snug
2) Comparison of bore i)Front- 8mm bore, ii) Rear standard 30cal bore
3) Three shot group from two moderators with different bores
4) Peregrine VRG4 - very pretty bullets!
more testing to come
Any chance of a PM reply please - thanks
even after its been on the rifle for 8 years and definitely works, yes, they’re may be quieter mods but it’s light, and if you try taking a shot with it off you soon realise it’s doing it’s job! 
