The above is all correct. Especially Barry.
I would look at having the end of the barrel portedas Roarless says then fitting an over/underbarrel tube, maybe fill it with steel mesh or wool if you really need to knock down noise. You could shorten it about as much as you like to legal limits obviously, without losing velocity.
Sparrow shot should be stepping out at subsonic velocities so I'm not sure why you think it's hotter?
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