I have extensive experience with .177 pellet guns. I have used and still use an RWS 34. That air rifle is accurate and relatively quite. After bending the barrel a couple of times, these long thin barrels are easy to bend, I decided to buy a side lever cocker. I bought an RWS Magnum 460 in 177.
This is as loud as my match 22 LR rifles! It is hard to say whether it kills squirrels quicker than the slower RWS 34. That rifle liked RWS Superpoint extra. While that pellet does not expand, it is pointed and it gives good penetration. For any air rifle, you have to test pellets. Some match, brand name pellets, would not group on a silver dollar at 20 yards. My RWS 460 loves Gamo Red Fire pellets.
Accuracy with these pellets is as good as any of the expensive match pellets I tested. These pellets will expand. I examine each pellet that I dig out of a squirrel and these Red Fire pellets consistently expand, the expansion depending on entrance location. Shoulder shots where the pellet hits bone, these pellets expand the most, behind the shoulder and through the ribs, less expansion. On yearlings, the pellet will blow through the rib cage of a squirrel, on older, heavier squirrels, the pellet expands and is usually caught under the skin on the far side.
These pellets lose velocity and I consider a 30 yard shot a long shot, anything 40 yards or further is basically out of range. A heavier, larger caliber pellet might extend this range. After dispatching enough squirrels I am conclusively in the Martin Fackler camp
https://en.wikipedia.org/wiki/Martin_Fackler : that is blood loss is a guaranteed kill mechanism. Seldom do squirrels die at impact, a good shot ends their existence within 15 seconds. That requires rapid blood loss. I have outstanding success by drawing an imaginary line from the near side to the far side shoulder and aiming at the entrance point on the near side. Any pellet crossing the upper chest cavity is bound to hit a lung, blood vessels, and squirrels that die quickly have their upper chest cavity filled with blood. It is unfortunate when the pellet hits below the lungs, in the stomach and intestines, as these squirrels run off and undoubtedly experience a suffering death. I have not been impressed with head shots, sometimes dead before they fall, sometimes not. A neck shot is extremely lethal as the pellet inevitably cuts blood flow to the brain, or breaks the spine. However, given all the inaccuracy in hold, pellet accuracy, it is my opinion that the best shot placement is upper chest cavity.