Little bit long. Found this article a few years back. Although it leans more likes sales pitch for one type the info is usefull
SUPPRESSORS OR SILENCERS AS WE KNOW THEM: WHICH TYPE IS BEST FOR MY RIFLE?
INTRODUCTION. Fitting a suppressor on a firearm is not a new topic by any means, but the number of such devices used by the general shooting populous is growing by the day in these modern times. More and more game farmers and other hunting outlets are realizing that the game on their facilities is less disturbed by hunters who use such a device on their rifle.
In consequence, there are a growing number of these facilities that prefer the use of suppressors by visiting hunters on the one hand, and on the other there are a growing number of rifle owners, especially those who own the larger calibers, who are finding that using a suppressor makes firing these rifles a more comfortable experience due to reduced recoil while also experiencing less damage to their hearing. At this point it is pertinent to look at the factors involved when a cartridge is discharged in a rifle from a chemical and physical point of view.
While these devices provide significant advantages, there are some critical drawbacks of which many rifle owners seem to be blissfully unaware.
THE ADVANTAGES OF FITTING A SUPRESSOR. Firstly, as the powder burns it produces a volume of extremely hot gas, at temperatures exceeding 3000°C, which is higher than an oxy-acetylene cutting torch. Most firearm users do not realize that the average rifle barrel only lasts approximately 1.7 seconds before it is worn to the extent that it becomes inaccurate. This is because that 3000°C heat has eroded the chamber area or other portion of the barrel to the extent that any projectile fired through it becomes unstable due to the influence of the discharge gasses on the projectile in the throat area or at the muzzle. There are many advantages in fitting a suppressor to your rifle over and above those related just to sound although this seems to be the main criteria.
1. The most important advantage of a suppressor is the hearing protection. Many have suffered permanent hearing damage due to muzzle blast. By reducing noise, recoil and muzzle blast a suppressor enables the shooter to follow through on the first shot and fire a second if necessary on the same target as wildlife is confused as to the direction of the source of the shot and hesitates before taking flight.
2. Suppressors reduce firing recoil significantly, primarily by diverting and trapping the propellant gas. Propellant gas is generally a fraction of the projectile mass, but it exits the muzzle at multiples of the projectile velocity, and since recoil energy is a function of mass times velocity squared, the elimination of the propellant recoil can be significant. The added weight of the suppressor also contributes to the reduction of the recoil.
3. A suppressor also cools the hot gasses exiting the barrel so that most of the lead -laced vapor condenses inside the suppressor thus reducing the amount of lead pollution that might be inhaled by the shooter and other bystanders.
The bigger the suppressor volume, the greater will be the effects on noise, recoil, cooling and pollution limitation
TYPES OF SUPRESSORS. There are three types of suppressor in the marketplace today and each has its advantages and disadvantages.
A. NORMAL SUPPRESSORS. Here the unit screws on to the end of the barrel and projects forward. This can add anything from 250mm to 400mm to the length of the rifle while weighing anything from 500 grams to l kg.
B. SEMI-REFLEX SUPPRESSORS. Here the unit extends rearwards over the barrel to a certain extent while still extending the rifle length by at least 200mm. They are of similar weight to the Normal type.
C. FULL REFLEX SUPPRESSORS. Here the unit extends rearwards over the barrel almost to the stock creating the biggest rear chamber possible and only extends the rifle length by a maximum of 150mm even for the largest calibers.
CHEMICAL AND PHYSICAL ATRIBUTES OF A DISCHARGING CARTRIDGE. When the primer is struck by the firing pin in a rifle and the charge of powder that is loaded is ignited the following scenario takes place in a very short span of time. Next is the volume of gas produced by the powder charge. This is a vital and very important aspect of this process. Sources show that 1 grain of nitro cellulose powder can produce approximately 20 cubic inches or 327cc of gas on combustion. To interpolate this, then 30gr of powder produces approximately 9836cc of gas and 60 gr approximately I9672cc of gas on combustion. In effect this means that those who shoot a .308, 30-06 or similar caliber creates about 9 liters of gas and those with bigger calibers produce 20 liters or more of gas on discharging a cartridge. Now remember that this gas produced is super-hot (3000°C) and must go somewhere! It is this super-hot gas that produces the recoil and noise. It is also this super-hot gas which causes throat or muzzle erosion which in turn causes the barrel to wear beyond the limits for accuracy. Look at the two main problems related to the type of suppressor you decide to fit to your rifle. They are:
A. A disturbed firearm balance, and most importantly,
B. Barrel Erosion at the muzzle end.
Looking at disturbed firearm balance first, the most obvious culprit would be the Normal type of suppressor where all of the device hangs forward of the barrel. Obviously the Reflex suppressor would be less of a disturbance as a good portion is over the barrel thus reducing the overhang, while the Full Reflex suppressor would cause the minimum of disturbance to the firearm balance. However, barrel erosion at the muzzle end, this is where the outcome of your choice has a major influence on muzzle erosion and should be the most important aspect of which type of suppressor you choose.
Now I am sure we have all seen that good old demonstration of what happens to the water in a rectangular basin when one end of the basin is given a good slap. The water rises up on the side that was given the good slap, and then takes off like a wave towards the other end, hitting this other end and forming another wave which travels back towards the side of the initial disturbance. This is exactly what happens to the huge volume of gas created when you fire your rifle when it enters a Normal type of suppressor.Except for that small amount of gas which is directly behind the bullet and follows the bullet through and out of the suppressor, the balance is caught by the baffles and forms a secondary wave which then follows the path of least resistance, which, by the time it starts to move is back towards the chamber of the rifle. Remembering that this gas is super-hot, it is this returning gas that causes excessive and rapid muzzle erosion. This of course can only be corrected by the re-chambering, shortening and accurate re-crowning of the barrel or the re-barreling of the rifle at considerable cost. Not a good outcome at all considering the expense.
The Reflex type of suppressor reduces the above phenomenon to a fair extent, but again, where do you find the space to "park" some 10 to 20 liters of gas until such time as it is safe to let it bleed out of the muzzle end of the suppressor?
THE ADVANTAGES OF THE FULL REFLEX SUPPRESSOR. This is where the Full Reflex Suppressor, comes in to its own. Firstly, it creates the minimum of disturbance to the balance of the rifle as the majority of the suppressor is behind the muzzle of the firearm. It also only extends the overall length of the weapon by 150mm or so and weighs almost the same as the lightest of normal type suppressors. However, when it comes to barrel erosion, this is where this type of suppressor excels in minimizing this phenomenon. Due to its extra-large rear chamber which extends back over the barrel the following advantages are achieved:
A large proportion of the produced gas is turned into this rear chamber producing:
1. Vast reduction in observed recoil.
2. An opportunity for this gas to cool down due to contact with the much larger cooling surface of the outer suppressor housing.
3. A brief break in the time between the pressurization of this gas into the rear chamber and the bullet clearing the end of the suppressor causing the largest reduction in pressure to be situated at the exit of the suppressor before the pressurized gasses begin to move towards the least resistance.
4. The turning of direction of this gas from moving towards the chamber end of the barrel, as occurs with a normal type suppressor, instead towards the exit of the suppressor due to the "basin" effect explained earlier is the most important aspect of the full reflex suppressor. This is the main cause of reduced erosion to the barrel area.
5. The much larger internal volume of this type of suppressor also allows these very hot gasses to cool significantly before they are introduced to any area of the barrel thus reducing erosion even further.
6. The significant reduction of noise below that of a similar weighted normal type suppressor due to the reduction in pressure caused by the change of direction in airflow achieved by this design is also a major benefit.
HAVING A THREAD CUT ONTO A RIFLE BARREL. It is very important to have the threading of a barrel done by a competent gunsmith. If the barrel is threaded incorrectly, it will suffer the consequences of having a rifle that will not shoot a good group whatever is tried, or a barrel may have with an inherent weak spot where the threading stops. Please remember that ensuring that the thread is cut concentric to the bore of the rifle is paramount to preserve the accuracy of a weapon. The reason for this is that the exit hole of the suppressor acts in exactly the same way as the muzzle crown of the rifle, if it is damaged or off-center in any way then the exiting gas behind the bullet will have the same effect on the bullet as would a damaged crown: unless the gas exits equally around the base of the bullet as it exits the suppressor, it will exert a disproportionate amount of force against the exiting bullet causing it to be deflected from its intended flight path. The result is inaccuracy!
There is only one way to ensure that the thread on the end of a barrel is cut concentrically to the bore and that is by ensuring that the barrel is held "between centers" in a lathe.
To do the barrel must be removed from the action for the threading operation to be done correctly and accurately. Some barrels outer diameter of the barrel is anything up to a millimeter out of concentricity with the bore. In such cases, if the barrel is just gripped in the lathe chuck and the thread applied, any suppressor, no matter which make or design, will cause the weapon to be inaccurate as the final exit orifice of the suppressor will be offset from the bore by the same amount. Then there is the matter of thread size. Some gunsmiths just apply a standard thread of say 14mm x 1,0 pitch irrespective of the caliber and barrel thickness, When one has a thick barrel of say 20mm at the muzzle, then cutting a small thread requires that a recess behind the thread needs to be cut to allow for the withdrawal of the cutting tool. The problem with this is that this creates two problems:
1. A potential weak spot in the barrel.
2. A portion of the barrel that cannot be threaded so that in the case of requiring to have the barrel re-crowned at some later stage, you will automatically lose at least an inch (25mm) of barrel length in this process.
Always try to use the largest thread diameter possible or at least a 16mm thread so as to give the maximum amount of 'flesh' between the rifle bore and thread thereby reducing the weak spot to a minimum. To avoid the requirement for a recess one can turn a step-down onto the barrel for 2mm to 3mm to allow for the threading tool to be withdrawn. This stepdown should be the same diameter as the thread to allow for thread continuation in cases where re-crowning is required. Turned a grove behind the thread to allow for the machine tool to clear the thread. Especially with big calibers this can result in this area being reduced to a millimeter or a little more in thickness creating a very weak spot in the barrel and no way to re-cut the crown without removing the whole threaded section. If you don't mind losing an inch or more of barrel length, or the inaccuracy which may occur from not following this route for getting the thread cut correctly you can use the other route. After all, it’s your rifle and hard earned money and your decision entirely.
A FEW QUESTIONS AND ANSWERS
1. DOES THE WEIGHT OF THE SUPPRESSOR DO ANYTHING TO THE ACCURACY OF THE RIFLE? Quite a number of years ago Browning brought out and patented a system known as the Ballistic Optimizing Shooting System or BOSS system. The system was in the basic a weighted collar that was fitted to the end of a rifle barrel which could be finely screwed in or out to set the weight at any distance required to balance the vibrations of a barrel. When a rifle is fired the barrel goes through a series of vibrations as the bullet travels down the barrel. Depending whether the bullet leaves the muzzle at a point where these vibrations are at the neutral point or not will make for a good grouping or not. The BOSS system could be tuned to provide the "sweet spot" where the barrel was at its neutral position and thereby provide better accuracy than could be obtained by an out-of-the box rifle. While any suppressor for that matter has been proven to damp the vibrations of a barrel in much the same way as this system due to the addition of weight on the end of the barrel, small changes in the load or bullet seating depth can also be used to achieve similar results if required. So you may find that you have to change your load or seating depth very slightly to get the very tight group you require if you fit a suppressor of any kind.
2. WILL A SUPPRESSOR AFFECT THE VELOCITY OF THE AMMUNITION THAT I AM USING? If you are using and old type silencer with 'wipes' (small pieces of rubber with an X cut to wipe over the bullet as it passes) fitted into it, then the answer is yes: the velocity will be less. Old .22 caliber suppressors used to be built that way, however with modem suppressors this is no longer a factor. The velocity of any bullet is dependent on the pressure of the gasses which propel the bullet until it leaves the muzzle of a rifle and the pressure escapes to the atmosphere. According to Nick Leghorn of Texas, who did tests using a chronograph and 5.56 ammo, he found that quite the opposite was true. There was a slight increase in the velocity of the same ammo with a suppressor fitted to the rifle. This increase can be due to the fact that the gas behind the bullet is there for a fraction longer in a suppressor. It is of such a small value however that for all intents and purposes one can forget about it.
3. HOW WILL A SUPPRESSOR ALTER MY POINT OF AIM? Any weight added to the end of a rifle barrel will cause the bullet to hit lower on a target. This was common knowledge for the Armed Forces who were taught to aim higher if they were shooting with bayonets fixed. The same can be said of a suppressor, so you will have to adjust your sights for the new point of impact which will be lower than before. A rifle’s point of aim can shift from anywhere up to 230mm left/right and low of where was aimed without the suppressor fitted. This is especially with the magnum calibers where the reduction in recoil and added weight has made the most difference to the original point of aim.
4. CAN I USE MY RIFLE WITH AND WITHOUT THE SUPPRESSOR FITTED? Whenever you fit added weight to the end of a barrel, be it a BOSS system or a suppressor, the harmonics of your barrel will be radically affected and due to the added weight which is acted upon by gravity, the rifle will always tend to shoot lower. Once you have adjusted your loads (by powder weight and/or bullet seating depth) to find the sweet spot again and then adjusted your sights accordingly, it is imperative to use that rifle in its new configuration at all times. If you remove the suppressor and attempt to shoot with the rifle as before, you will have to go back to your old loading data as well as old sight settings otherwise you may find yourself completely off the target.
5. WHAT IS THE DIAMETER OF THE FULL REFLEX SUPPRESSOR? The Full Reflex Suppressors are made in two popular sizes. The first is the standard nominal 50mm diameter size which can be fitted to most rifles irrespective of caliber. The second size is 62mm diameter. This is for those who wish to have an extremely quiet weapon such as for sniping, and are more interested in performance than aesthetics. This size requires in some instances that the scope be mounted on higher mounts or a Picatiny rail to allow for a full sight picture. It is however extremely effective reducing recoil by almost 70% and reducing the weapon firing signature and noise by virtually the same percentage.
6. HOW SHOULD I STORE MY RIFLE NOW THAT A SUPPRESSOR HAS BEEN FITTED? Because you are now using different loads with the suppressor fitted to your weapon it is advisable to store your weapon in its ready state with the suppressor in place. When a suppressor is fitted to a rifle, the optimum way of storing the weapon is with the bolt removed and with the barrel pointing down. The reason for this is as follows: Water is a major by-product of gunpowder combustion. A good suppressor will capture and retain a considerable amount of the liquid. Twenty shots from a .308 will cause about a teaspoonful of water to be captured. The bolt or action should remain open to allow accumulated water to evaporate and vent. Unfortunately, most rifles are traditionally stored muzzle-up. This causes water and trapped particulates to slowly release, where they will fall and lodge in the chamber area and bolt face. Burned gunpowder is quite dirty, and the inside of a suppressor can become quite filthy after an extended period of shooting. One should get in the habit of storing a suppressed rifle by standing it, muzzle-down with the end of the suppressor standing on a piece of wood which has been slotted so that there can be a free passage of air through the suppressor and the barrel. Even stainless steel components will rust if trapped water is not allowed to vent. A bore with rust near its muzzle may lose its accuracy. Corrosion can occur fairly quickly in a warm and especially moist environment.
7. ARE THERE ANY FURTHER ADVANTAGES OF USING THE FULL REFLEX SUPPRESSOR OVER THE NORMAL TYPES WHICH JUST SCREW ONTO THE END OF THE BARREL? A suppressor that is held at the rear by a single collet, or by a single section of threads, is said to be held by a single-point mount. Unfortunately, many suppressed rifles with single point mounts suffer from a wandering zero. There is, however, a better way. The two-point mount usually attaches a barrel to its suppressor with threads at the muzzle, and with a collet, O-ring, or conical joint about 20 to 25 cm or 8 or 10 inches behind the muzzle. It is a vastly superior way to mount a suppressor to a rifle barrel. The resulting joint is many times stronger than any single-point mount could ever be. Because of the geometry of a two-point mount, a small error in alignment will not progress into a much larger error at the suppressor's muzzle. This system provides the best accuracy especially if the suppressor is removed and refitted a number of times.
IN CONCLUSION. A decent rifle in today's world cost you a an arm and a leg and is not the sort of item that can be replaced at the quick decision of a whim. Most people only ever own two or three different calibers dependent on what they can shoot and afford. Now, in the same manner as the fitting of inferior optics to a good rifle creates an inferior tool for the hunter, so can the fitting of an inferior suppressor cause your pride and joy to become that embarrassing piece of hardware which does not seem to be able to hit what you aim at after a relatively short space of shooting time. The FULL REFLEX SUPPRESSOR is the only type to fit to your good hunting rifle, because it just makes good sense, all factors considered.
