The grips look to be made of Casein, a plastic made from milk proteins. These have been around for a long time, so your pistol may be older than you think.

You may find it interesting to compare .22WMR with Winchester Z. The Z is a pistol round which may give you a similar penetration (phone books give a measurable penetration) without the staggering muzzle blast.

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Calm, quiet, smooth, devastating