The Crosman 1088 Pellet/BB is rated at 400-430 FPS
See the related link at the bottom of this page to see the Crosman 1088 parts manual.
see the link below
see the link below for the owners manual
It would really help if you stated the manufacture of the 1088. So I'm going to guess it's a Crosman. See the link below
Yes but it is best to make it a head shot, or the squirrel will suffer and die.
Crosman has a web page for their owners manuals and part list. See the attached web page. you will find your 1088 listed about half way down on the page. The parts last will give you an exploded view of the gun. See the related link
see the link below for the Owners manual.
If it's not on the outside then very possibly it's under the grip cover
Depends on what is wrong with it. You did not say.
It all depends on what is wrong with it.
If it's still under warranty I would send it back to Crosman or at least contact customer service at Crosman. WWW.Crosman.com