how to preserve squirrel pelt.

[Mr. 16 gauge]

What do you mean by "preserve"? Do you want it soft and pliable, or do you just want to keep it from rotting so you can put it on your wall?

If it's the latter, then just make sure all the meat is off the hide, and rub in a good amount of noniodized salt to dry it out.
If you want it pliable, there are tanning kits from the various taxidermy supply houses that you can use for that purpose.