Pneumatic air guns like your Sheridan do have recoil, then, but you'll mostly see it as muzzle jump, rather than a push back against your shoulder. We tend to ignore recoil in pump ups, PCPs and single stroke pneumatics because it is so mild, but it's still there. It's technically incorrect, then, to say a PCP does not have recoil, but compared to the recoil of piston guns it's so mild as to be not a factor in our shooting, so we sometimes get a little sloppy with our terms.
In fact, even that little bit of muzzle jump caused by recoil in high end competition PCP pistols like my Steyr, above, is enough to affect scores in this very exacting completion, so these high end competition PCP target guns use barrel vents to to keep the muzzle jump down.
And then there are piston guns. Why do these have so much recoil compared to pneumatics?
In a pneumatic, the air has already been pre-compressed before you trip the trigger, either by pumping or pre-charging. With your Sheridan, you've already done the work needed to compress the air with however many pumps you used to charge the gun. With your Sheridan, the only part that moves when you pull the trigger is a small valve part that opens to dump the compressed air. Same with a PCP. Only the air pushing that light pellet out of the barrel is producing recoil.
With a piston gun, air has yet to be compressed when you pull the trigger. This is the key to understanding why piston guns produce recoil. That pellet is sitting in the chamber with no compressed air in the gun. When you pull the trigger, a piston under compression from a powerful spring or air cylinder slams a piston forward at high speed to compress the air in the cylinder and deliver it to the pellet. Only then does the pellet move down the barrel. This has two consequences for the shooter of a piston gun.
The first is the recoil produced by the release of that powerful spring or air cylinder on a piston that then has to move forward at high speed to compress the air. The spring and piston moving forward cause an equal reaction to the rear and causes the gun to recoil to the rear. This part of the recoil in a piston gun is actually pretty mild and is mostly absorbed by the mass of the gun.
The second part of the recoil is much more pronounced. The spring and piston moving forward at very high speed slams to a stop. The air compressed ahead of it sends the pellet down the barrel. That forward momentum of the fast moving spring and piston slamming to a stop is then transferred to the gun and the gun moves forward, producing that unique forward recoil you only get get with a piston gun. The stronger that spring and the more massive the piston, the more pronounced forward recoil. This is the recoil that can eat up a scope not rated for piston gun use in a hurry, because typical scopes are designed only to handle rearward recoil.
There is another factor with piston guns that doesn't get much discussion, because it is much less noticeable compared to the recoil, but it does make a piston gun a bit more challenging to shoot. This factor is lock time, that being the time it takes for the pellet to leave the barrel. In a piston gun, you have to wait until the air is compressed by the forward moving piston before the pellet even begins to move down the barrel. Not so with a PCP. The air is already compressed when you pull the trigger. A PCP rifle that has a muzzle velocity of 900 fps, then, has the pellet out the barrel significantly faster than a piston rifle that sends the same pellet out the barrel at 900 fps. The difference is only in milliseconds, but as competition shooters know (even in the cartridge gun world), a faster lock time makes follow though less critical.
The bottom line with learning how to shoot a piston gun is learning how to handle the recoil so it doesn't destroy accuracy AND developing top notch follow through to handle the slower lock time. It can be done, of course, but it does put the shooter at a disadvantage when competing against a PCP gun of equal quality. This is why PCPs guns own all competitive air gun shooting competition. In sports like Field Target that even allow piston guns, piston guns have their own category so they don't compete directly with PCP guns.
For shooters new to air guns, no special skills are needed to shoot pneumatic air guns, other than developing good follow through for the lower fps of air guns. Piston guns offer a lot of advantages - my favorites - but it comes at the cost of learning the techniques to shoot them, well.
Whew! HopeI didn't put too many of you to sleep.
