For shooting pests, stick with the lead pellets. Air rifles are finicky. Once you find a pellet it shoots well, stick with it. I use a 22 caliber spring air and it is pretty accurate. The alloy pellets are not that accurate and break the sound barrier so they are noisy compared to the slower lead. Some of the air rifles are suppressed (yes it is legal without a tax stamp) and are really quiet after the first 50 rounds. I have found it takes about 50 rounds before a new rifle settles down.
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"I would not be an old man if I had not been an armed young man." JTJ
I was taught to respect my elders but they are getting harder to find.