Generally, you cannot shoot within 50 yards of a public road, or within 100 yards of an occupied dwelling. Both are DCNR "hunting" regs. There are some exceptions to both though.
I am not aware of any state law that addresses the specific size of a piece of property for use as a firing range. Local ordinances may very well address that issue though. Also look into laws regarding discharging a firearm within city limits, reckless endangerment, and noise issues.
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