I've never fired a supressed weapon so I have no real knowledge of the subject, but does a suppressor reduce recoil? Since the bullet typically weighs so much more than the ejected gas leaving the muzzle I wouldn't think it would make a lot of difference. It adds weight to the muzzle and I'm sure that would help some. (Italics mine)
The theory of recoil is rather complicated, and there is an extensive discussion of it in Hatcher's Notebook.*
However, the ejected gases do create a substantail amount of the recoil.
You can look at it several ways, but one way is to remember that a typical .30-06 cartridge may have a bullet weight of, say, 150 grains, but there is also about 45 (or more) grains of powder gas which is also being ejected --and this is about a third the weight of the bullet, so it must inevitably make the gun recoil as it is thrown out. (Remember, the weight of the unburned powder is the same weight as the resulting gases from burning that powder, and around 45 or so grains is about right for the .30-06 in my recollection.)
The question of suppressors reducing recoil aside, another way to look at recoil from the gases is that it is well known that shorter barrels kick more in the same cartridge than longer ones --even though the bullet weight is the same. (They are also noisier, as is also well known.)
Just to illustrate conceptually how the powder gases can affect recoil, the peak pressure developed in a .30-06 rifle barrel occurs more or less when the bullet is 2 or 3 inches down the barrel, and may be around 50,000 psi. By the time the gases exit the barrel, they are down to about 5,000 psi.
Roughly speaking, as the bullet exits a full-length barrel, suddenly there is an
unbalanced pressure against the breech of about 5000 psi, which results (again, roughly speaking) in about 350-400 pounds of instantaneous force (thrust) against the breech.
But as you cut the barrel length down, the pressure in the barrel at time of bullet exit gets greater and greater. Hence that instantaneous force against the breech is greater and greater as you cut more and more off the barrel.
If you cut the barrel down to where the aforementioned pressure peak of, say, 50,000 psi, is reached, that means when the bullet exits there is a lot more instantaneous force on the breech because of the greater pressure. At 50,000 psi, this instantaneous force (thrust) is about 3700 pounds, far greater than with the full-length barrel.
So the gases themselves can produce a substantial amount of recoil, and the effect is more and more noticeable in shorter and shorter barrels.
And of course, as the release pressure goes up, so does the resulting muzzle blast.
Hatcher, in Hatcher's Notebook, goes into great detail explaining exactly how much of the recoil is due to the ejected gases. It is substantial.
Again, though, this is only in answer to your question of whether there is much recoil from the gases in the first place, and why. And you are correct that the additional weight of the suppressor reduces recoil*.
Terry, 230RN
* REF:
Hatcher's Notebook by Julian S. Hatcher (Library of Congress 62-12654). There is an extensive discussion on pp 284ff of the three elements of recoil: due to the bullet, due to accelerating the powder gases, and due to the muzzle blast from the sudden release of these gases. Hatcher, by the way, distinguishes between the psychological "kick" versus the pure physics of recoil in an earlier section. He also discusses both suppressors and recoil compensators in other sections of the book.
NOTE: There isn't much point in suppressing a .30-06 since the supersonic crack of the bullet itself is so loud, but I have used it as an example here since the "workings" of the .30-06 service cartridge is so well known.
