Full Bore Moderator Test

Introduction

Nothing in recent times causes more controversy and consternation than rifle shooters talking about what is the quietest sound moderator on the market. In my time I have had a real passion for silenced rifles of all calibres and forms. In the early days it was easy as there were only a handful to choose from, but today lots of companies are competing in the market – so which is best?

There is only one way to test a sound moderator, be that rimfire or full bore and that is to use a professional sound meter, and in this case one costing £5000 plus. Then you need to set up a test area that conforms to the internationally recognised test procedure, that is Mil STD 1474C.  Only in this way can you compare each sound moderator on its own merits when tested side by side with comparable units under the same conditions from the same gun using the same ammunition and at the same location.

Hopefully these totally unbiased results should give you an insight into what is good and what is not. The only caveat is that sound moderator manufacturers seem to change their specifications daily, and some use decibel (dB) reduction figures in their advertising is not to Mil STD 1474C.  In this test because of the enormity of the range of moderators, I have chosen the most common on the market and those that were willing to be tested! I have also used three differing scales of measurement that I always get asked about, only the Peak “A” weighting scale is relevant for these tests but you can see why some manufacturers quote the Impulse noise results not the Mil STD ones, because it gives a false result of the true decibel reduction.

The Test Regime and Equipment

There are only two sound meters that perform to the correct standards. First is a Larsen Davis Laboratories and secondly the Bruel and Kjaer Type 2209 which is the one I had on test. Still this is not enough as the correct microphone attachment is essential to actually “catch” all the incredibly fast rise time of the sound produced from a full bore rifle. In fact the microphone is the most expensive single part of the machine. This allows you to catch or record the “whole” muzzle report not just part and it was correctly calibrated with certificate of proof.

To ensure that each moderator was tested identically the same .308 ammunition supplied by Winchester was 150 grain soft point with a muzzle velocity of 2689 fps from my Tikka M55 rifle with a ½ inch UNF thread. The weather was 19.6 degrees Celsius and the barometric pressure was 1015 hPa with 5% humidity and the test location was in a large grass field with a slight rising ground to the front 49 feet above sea level.

The rifle was supported on a tripod exactly 1.6metres (5ft) off the ground horizontally with another tripod arm indicating the position at which each moderator was to be placed for uniformity. Next the B&K sound meter was placed exactly 1.6m high and 1.0 metres left from the sound moderators end cap. I shot three shot groups and recorded the results.

It is important to set the meter correctly, this means recording sound as Peak “A” or “C” Weighting not as an Impulse sound as this will not record all of the sound. I did however record the impulse sound readings as well, just to show the difference and thus the confusion when some manufacturers display their results!

The Results

Brace yourself, there are some really interesting results here. I have arranged them in a table so you can compare each moderator, maker, dimensions and three dB readings of which the “A” weighting is the correct one to use. The net reduction shows actual reduction in decibels so you can compare each moderator like for like.

The readings show three shots in order and so you can see if any of the sound moderators suffer from the dreaded first round “pop” problem where initial oxygen in the sound moderator is burnt increasing the dB reading.

The Tests

Remember a .308 rifle with factory ammunition is a hard test for a sound moderator and smaller centrefire such as .223 will be more efficient and have greater net dB reduction results. That’s why you see a range of dB reduction figures quoted by manufacturers in their literature i.e. 21-25dB.

You need to take the “A” weighting figure and not the Impulse sound as it’s like comparing the sound with and without ear defenders on, you will get a false result.

Firstly, in my view, it is not all about the biggest dB reduction as the size, weight, cost and material used in manufacture are all important. There is no point having the quietest moderator to find it is too long or heavy for your rifle. Study the results and see what would suit your own style of shooting.

Also remember that manufacturers are always competing with each other to gain a few more dB reductions, reduce cost and saving weight from the opposition, so these results are correct as of Jan 2011, and things may have changed already!

First of all an unsuppressed .308 report was recorded as the bench mark standard which gave 167.8 dB result for the “A” Weighting result, comparable to military tests results. This was nearly the same for the “C” Weighting results at 167.9 Db but the Impulse sound was only 150.2 dB which instantly shows you that Impulse sound results are not recording ‘all’ the sound. I only tested some moderators on “C” Weighting as there was little difference from the “A” Weighting but it gives you an idea of what’s going on.

Best noise reduction was jointly held by the MAE T12 and the Jet Z Compact at 26 dB reduction in noise, very good for a 21 inch .308 rifle with full power factory loads.  The MAE T12 is an over the barrel design and stainless steel whilst the Jet Z Compact is steel construction and muzzle mounted so the choice is yours, look at price, size and weight to make up your mind.

Second quietest were the Wildcat Predator T12 over barrel and the muzzle mounted LEI Compact , just goes to show the older design muzzle cans can really keep their own against newer but not necessarily better designs. A reduction of 25 dB is very good but once again, check out the size, weight and cost difference.

Third place went to the North Star moderator at 24 dB reduction and this is a stainless steel over the barrel type without a rear bushing so is conveniently fitted to most types of rifle barrel.

There were three moderators in fourth place at 23 dB reduction , the MAE 30STS muzzle can, ASE Utra S5 muzzle can and Reflex T8 over the barrel , again very interesting results from differing designs and materials used.

Finally fifth place with 21 dB reduction is jointly awarded to the A-Tec CMM aluminium muzzle can and Brugget and Thomet steel muzzle can. There is a big weight difference between each moderator and price, and the A-Tec comes apart for cleaning whilst the B&T is a sealed unit.

Conclusions

In reality you can see that the actual decibel reductions are quite close across the board, so I suspect your own choice will be dictated on how big is your wallet, whether you want as short a rifle overall length as possible, or if the corrosion resistant properties of stainless steel are important to you, or do you want the lightest weight possible? All these are important factors and should be weighed up against the raw sound reduction data. I hope these tests help you make up your mind.

Contacts

Ace Utra, Northstar, Jet Z Compact, S5, A-Tec CMM, Reflex T8 (Jackson Rifles tel.01644 470223)

MAE 30STS & T12 (JMS Arms tel.01444 400126, 07771 962121)

Predator T12, Wildcat (UK Custom Shop tel.01905 797060)

LEI (LEI tel. 01727 826607)

Brugger and Thomet (Viking Arms tel.01423 780810)