From another website:
"Suppressors reduce the firing signature (both flash and dust/vegetation), reduces recoil and reduces sound. Unless shooting subsonic ammo, the supersonic crack of the bullet in flight will still be heard.
Suppressors do not reduce accuracy or the terminal ballistics of the weapon. With regards to accuracy and suppressors, depending on quality, you can have a suppressor that provides a return to zero when taking off and on, suppressors that have a constant POI shift when attached, or you can get suppressors that needs to be zero'd before use."
"To expand a little bit on what suppressors do:
1. Increases the internal pressure of the firearm -> increased wear on parts
2. Blows more gas back in to the action -> increased fouling
3. Adds weight and OAL to firearm -> amount varies with suppressor design and construction
4. POI shift -> added mass to barrel affects barrel harmonics, causing impact shifts. Most reputable manufacturers have suppressors with consistent POI shift, as well as return to zero when taken off and mounted again. How much will depend on suppressor type
What they do well:
1. Reduces felt recoil because it captures and traps the propellant gases, releasing them slowly out of the barrel, compared to an unseppressed firearm where the gases shoot out the muzzle like a rocket
2. Reduces flash signature because of the above, and because the propellant has increased burn distance
3. Reduces noise signature of the expanding gases leaving the muzzle at fast speeds, by capturing and trapping the gases inside the suppressor -> supersonic crack of projectile will still be heard, unless subsonic ammunition is used
4. Some suppressor designs can increase the velocity of the projectile
5. Some suppressors increase accuracy -> can be due to change of barrel harmonics, change/calming of turbulence around bullet when leaving muzzle"
"Suppressors can increase muzzle velocity through a very simple physics formula.
Basically the suppressor makes the barrel longer. Therefore, it increases the distance the bullet must travel to leave the barrel. Because it takes longer, the force of expanding gas is acting to accelerate the bullet that much longer as well. The longer the bullet is being accelerated, the higher is the exit velocity.
From the Newton's law, it is impossible to increase velocity and reduce recoil. If you look at the rifle as an isolated system, then whatever force the expanding gas delivers to the bullet, same force must be delivered onto the rifle. The net recoil from firing a suppressed weapon may be PERCEIVED by human to be lower, simply because the impulse takes place over a longer period of time (see the first part of the comment), but the total energy transfered into the shoulder is greater.
If you introduce the concept of a muzzle break, then you are indeed reducing total recoil, but then it cannot possibly be a suppressor simply because of its mechanics."
"Well, didn't intend for this to become a physics discussion, but since you threw down the gauntlet, I have to pick it up.
First of all, let's define recoil. Recoil consists of two physical aspects:
Primary Recoil is what you are describing in your post, the momentum of the bullet traveling in one direction, and the momentum of the rifle traveling in the other direction. This is where Newton's 3rd law comes to play -> equal and opposite reaction. The physics that explain this primary recoil is conservation of momentum. This is NOT the recoil mainly felt, but it is noticeable. The primary recoil cannot be reduced, since it only represents the conservation of momentum of the gun-bullet system.
Secondary recoil is a result of the escaping gases from the muzzle, causing the muzzle to recoil like a rocket. This is the main recoil felt when shooting a firearm. This recoil can be reduced by adding muzzle devices to redirect the escaping gases.
Now, on to your statement, that recoil will increase because a suppressor provides longer travel for the bullet and more room for the expanding gases to accelerate the bullet, thus increasing the velocity. There are two issues with this statement:
1. You neglected to add mass to the equation, from the suppressor. Even though both values increase, the net effect might not be an increase in recoil.
2. A suppressor does not function as a bore, so what you are describing does not happen.
I'll adress point number 1 first.
Let's throw down some numbers to illustrate the effects of primary recoil on a rifle, first unsuppressed, then suppressed. Let's say that the gun is a .308/7.62, shooting a bullet that weighs 150 grains/9.7 grams at a velocity of 2820 ft/s, or 859 m/s. The gun weighs 9.9lbs/4.5 kgs without a suppressor.
Momentum (P) is mass (m) times velocity (v), or P=mv. Let's work out the momentum of the bullet (b).
Pb=mbvb or Pb=8.3kg m/s
The momentum of the bullet is 8.3kg m/s in the forward direction.
Now, since the net momentum of the system must be zero, the forward momentum of the bullet is balanced by the rearward momentum of the gun (g):
Pg=-Pb or mgvg=-mbvb
In our example above, with a weapon having a mass (mg) of 9.9lbs/4.5kg, the recoil speed of the rifle is:
vg=-Pb/mg or vg=-1.84 m/s
Now, let's add the suppressor. For this example, let's say it adds 40 ft/s or 12 m/s (an actual number I found online). This makes the new velocity of the bullet 2860 ft/s or 871 m/s. The weight of a Gemtech .308 suppressor I found was 17.5 oz, that equals 496 grams or 1.1 pounds. The new weight of the rifle is 11lbs or 5kg.
Momentum of bullet suppressed is Pb=8.45kg m/s
The recoil speed of the gun will be vg=1.69 m/s
So, primary recoil is in fact less suppressed, than unsuppressed.
Next is a picture where I used a recoil calculator to work out the free recoil energy of the same gun unsuppressed and suppressed. Load 1 is unsuppressed, Load 2 is suppressed:
As you can see, there is more free recoil energy in the unsuppressed gun, than there is in the suppressed gun.
Now to point number 2, how a suppressor actually works. You stated that the suppressor adds OAL to the bore of the gun, giving the bullet a longer distance to travel, and getting affected by the expanding gases over a longer period of time, thus increasing velocity. Well, not exactly.
The inside of a suppressor is not a bore. If it was, it would not reduce the muzzle blast or flash. The loud muzzle blast is a result of the hot expanding gases escaping the bore, and hitting the colder air outside the gun.
A suppressor is a cylindrical container and, depending on design, is divided into several chambers by baffles of cylinders. These baffles or cylinders capture the gases behind the bullet, giving them more room to expand and burn off propellant, thus slowing them down as well as cooling them down. The result is reduced noise and visible flame from the muzzle blast.
Here is a few vids of how suppressors look disassembled:
The actual phenomenon that causes the increase in velocity is called freebore boost, and is caused by the expanding gas inside the suppressor still pushing on the bullet, without the drag of the rifling affecting the bullet, leading to a slight increase in velocity, numbers vary between 10-50 ft/s. It not nearly as effective as additional length of bore, which can add 50+ ft/s per inch of extra bore.
Muzzle breaks on the other hand do not reduce noise from muzzle blast, as it does not slow or cool the expanding gases. It does however divert the expanding gases to the sides or up, in order to counteract the muzzle flip caused by secondary recoil."