Hunting Kid - I never got good accuracy using Crossman pellets in my .17 cal. guns. I always had the best squirrel killing results using the RWS superpoint 8.2 grain pellets. I regularly killed gray squirrels stone dead with them out to about 35 yards, trying mostly for head shots.
Keep in mind - that every air gun is a law unto itself as far as the ammo it likes. It sounds like you don't have a lot of money to experiment with different pellets - so it might be a good idea for you to go to one of the on line airgun stores and buy one of their pellet samplers, and try as many pellets as you can, to see what your particular gun likes the best.
I assume you are shooting the big Fox squirrels and they are a bit tougher to anchor than a gray squirrel. If you can - try to get a .22 cal. pellet gun when you get a chance to trade up - you will be amazed at the killing difference.
Also - In my very limited experience - I have found that it pays to pay a little extra money for the RWS or H&N pellets - accuracy wise and for the killing power.
Hope this helps
Good hunting
P.S - I don't mean to be flaming you - but try to go easy on the chipmunks - ok? It was taught to me by an old guy many years ago, that you shouldn't kill anything you weren't going to eat. I know - when I was a kid - there for awhile - just like most kids - I shot most anything that moved too - till that old guy caught me killing dinky birds one day and had a long talk with me about being a responsible gun owner and hunter. That changed me forever.