A buddy of mine was concerned about ejection port pop on his suppressed KP9, so we weighed the reciprocating mass.
17.1 oz. This is pretty light, close to as low as is reasonable, unsuppressed.
For reference, the cheapest 9mm ARs usually have around 18oz, and the heaviest I can piece together (including a handmade bolt weight) and still use a collapsible stock is 29oz.
The setup I usually use has 20oz, and the typical setup that has nothing crazy, but a cheap 9mm solid buffer comes in around 23oz. A5H4 puts it around 22oz, IIRC. Those are all pretty well suited for suppressed use, and just fine unsuppressed.
Some competition 9mm ARs are in the 16oz neighborhood, running on very light handloads exclusively.