By Chris Parkin
Over my shooting career, moderators have changed from an unusual addition to a rifle that surprised people, to an almost integral part of the rifle, scope and mounts package. The UK seemed to be one of the countries at the forefront of civilian use with several UK manufactured brands as well as Scandinavian stalwarts. Early moderators were heavy steel units, great at suppressing noise with intrinsic vibration damping too, but heavy and prone to life as a consumable product with corrosion a serious factor to consider. Being sealed units also made them pretty much impossible to clean other than shaking out as many of the rust particles as possible. Those that doused them with sprayed anti corrosion lubricants soon got used to an enormous gas cloud emitted on the following shot, along with a somewhat noxious smell. But personal comfort with less hearing damage was much appreciated, along with the additional benefit of fewer complaints over surprise noise when urban foxing in the middle of the night. When tackling groups of animals in multi shot scenarios, there was an immediate benefit to confusing the direction from which noise had come, if not that there was at least something untoward happening and this often made the immediate evasion direction less certain to them.
The market is now far broader, moderators aren’t just appreciated, they are often mandatory in some locations and a variation for one is no problem, even for target use rather than just hunting. Benefits are primarily personal hearing protection, they don’t outweigh the need to consider other ear defence, especially if used on a range but for single shots you are now rarely bothered with short term tinnitus even though damage will still accumulate long term. The noise projected in the direction of the quarry is also more dispersed and although never silent, alters the balance between sonic crack and possible backstop impact noise whereby you might be more likely to get an opportunity with a follow up shot if needed. Carrying on from that, muzzle flash to a lesser or greater extent is certainly shielded more from view, away from the gun and from through your optic. The target is less likely to be obscured by flash allowing better appreciation of impact and at night, far less effect on night vision capability from your own eyes. When using NV equipment, particularly if filming, moderators will allow better view of impact position, terminal ballistic effects and with an additional illuminator, possibly even seeing the light source instantaneously reflected back from the bullet in flight. This further couples alongside recoil control. Sound moderators add weight to the rifle at the business end, both lessening muzzle flip and linear recoil pulse as some of the gas ejected like a jet is diverted and slowed, both being beneficial factors. Weight in itself has to be considered along with the overall length of the rifle in terms of portability but it’s generally seen now that the benefits of a sound moderator are well worth the additional rifle bulk.
Moderators seem to fall into a general three-way balancing act of sound reduction, recoil control and longevity. Stainless steel with improved resistance to atmospheric and gas corrosion from the rifle’s discharge, are far more common now and with complex modular assembly rather than a purely welded structure, moderators can be both disassembled for cleaning and use materials with properties far more relevant to individual position in the mod. For example, the external tube of a moderator, the greatest element you can physically see, is satisfactorily made from 7000 series aluminium whereas inner baffles, especially the first blast baffle, are better made from stainless steel with higher chromium content to resist corrosion or nickel where gas cutting is fierce from the internal blast of hot propellant from the bore. My general findings are lighter aluminium `cans` will also heat up more quickly to dissipate heat, and cool more quickly with a large surface area exposed to the cooling atmosphere externally. Being low density, thicker aluminium can be used than Titanium, which is a very strong, medium density material allowing less to be used but it’s thin body dimensions, although light and strong, get hot very fast and if follow up shots are needed, will quickly exhibit mirage.
Consider stainless steels for the external can, well they are denser and generally lead to a heavier moderator but suffer corrosion less than the non-stainless steels of old. These heavier moderators are very tough, durable and the mass itself absorbs the heat from the blast more slowly, often allowing a longer shot strings before it becomes a disturbance to the sight picture. The flip side is they can be slower to cool. Mirage bands and moderator shrouds can help with these matters but be aware of one overall fact…the barrel/moderator is a vibrating system, and you chose or tune your ammunition to work with its natural harmonic frequency. If you add mass, or change that barrel in any way, do not be surprised to see your point of impact change slightly on target and require a re-zeroing. If you use a fabric shroud, take care when removing and re-fitting to make sure any straps used are tight and not flapping around which may well affect harmonics randomly. Finally, just because a bullet hits slightly lower or higher on target at the fixed zeroing distance, don’t assume it’s slower or faster than before, it’s simply the change in harmonics, where in the circular oscillating cycle the bullet is when releasing the bullet from the crown. Yes, a moderator may also add a touch of weight that will make the barrel droop slightly, but this is microns, not centimetres, it only shows up because the target is hundreds of metres away.
So, what would I chose, well for a stalking rifle, I like a light moderator, one that will silence a single shot and allow a backup with no problem, aluminium and titanium is ideal, but the latter can be disproportionately expensive! I use many brands but return regular to Wildcat for the modularity. For a target rifle or varminter where my shot count is higher, I err towards heavier stainless-steel units like ASE UTRA Northstar on my 223 Varminter and SL5 on 6.5mm/308 precision rifles like the Accuracy International AT. The SL7 fully extends beyond the, still compact, yet restrains 338 Lapua Magnum all day long on the range. The stainless steel offers excellent durability when portability is not a huge factor to consider. Sound suppression is also excellent and there is nothing to come lose. Modular moderators with compound construction are generally threaded together in a tubular format and slow cleaning but make sure you use suggested high temperature anti-seize lubricants on threads as firing residues under high pressure will find every little nook and cranny in a threaded structure, these can soon become locked up solid if not regularly attended. Benefits of such systems, like the Wildcat range are that you can have one moderator for several rifles even if they have differing threads, additional primary blast baffles with differing threads can be purchased and an assembly system is used that accommodates disassembly more easily. Just make sure any moderator is in itself tightened in all regions as well as to the barrel with well aligned thread, cleanly cut. Think back to the high-pressure gasses lodging minute particles anywhere they can get. Correct anti-seize lubricants used sparingly also help avoid galling and bi-metallic corrosion, a hot moderator tightened hard onto a hot barrel can become incredibly tight to remove when the system cools down. Do not force a thread that isn’t smoothly running, you are inviting damage and believe it or not, tolerances between manufacturers do vary even though many proclaim industry standards are maintained.
ALWAYS remove the moderator after a shooting trip, they can and will form condensation inside. This is especially bad as most of use store a rifle in a cabinet, muzzle upward hence the moisture will descend down the barrel and form characteristically bad corrosion in the last few, most critical centimetres of the rifling. If you find that removal and refitting a moderator changes your zero, this is most likely down to a bedding issue (where the rifle action is held within the stock) which you likely, even non aggressively use to effectively hold the rifle (therefore use as a lever) when removing or re-fitting and tightening. If the rifle moves in the bedding/stock, this can be the problem, not the moderator itself and this is different to the harmonic changes from shooting with a moderator on or off which you have to account for in any zeroing setup should you chose to use a rifle in both states on a regular basis.
No moderator will truly restrict all noise but with protection around 25-33dB available from different models, it is as appreciated for personal protection as much as ear defenders so with both, as I prefer professionally, you are doing all you can to avoid problems long term. Bore size has some effect on this in terms of using the nearest bore size available for your cartridge but the physical volume of the moderator can’t be beaten, as a general rule of thumb the higher the moderator volume and the more in front of the crown, rather than “reflexed” behind it, the more moderation you get. The volume is there to restrain and temporarily retain that fast hot booming gas expansion the internal baffles strip from the column of hot propellant following the bullet. After all this, we must mention the 22 rimfire for whom a lot of these rules hardly apply. With subsonic ammunition creating no supersonic `crack` in flight, much lower gas volumes, speed and heat created, I leave those in place on the rifles I use them on. These have been far more commonly seen for much longer than with centrefires and are one of the gems of the shooting world where it really, nearly almost becomes a true `silencer`. Similarity with Air rifles, modern precharged pneumatics with efficient regulated gas flow are incredibly quiet with little mechanical noise and yet still benefit from sound moderators to confuse direction and minimise disturbance in the close quarters scenarios they are used in. I have been getting great results with SAK on 22 rimfire for years and recently appreciated the Donny FL on both FAC and 12 ft-lb air rifles where the effects are personally experienced and able to detect even the slightest reduction in volume/dB.
[gallery ids="728,725,724,727,726,723"]
Images:
- Wildcat showing different materials appropriate to location within the gas flow
- FX Impact Mk3 with Donny FL moderator
- Steyr CLII SX Mountain in 223 with Wildcat moderator
- CZ 457 Carbon appreciates the sound of silence using a SAK moderator with subsonic ammunition
- CZ 557 Eclipse in 308 Winchester being tested with moderator fitted, dont assume changed impact point when re-zeroing is from velocity change
- Wildcat Predator 12 on my own 260 Rem rifle, incredibly quiet but heavier and longer