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With a 45 grain cast bullet and 5.2 grains of Red dot the velocity is 1795fps hardly subsonic it would be slower with a jacketed bullet but not by much

Drop the bullet weight to 35 or 40 grains the heavier bullets are too long to stabilise at sub velocity, The only .22 centre fire cartridge that is viable for subsonic is the .22 Hornet
the case...