Quote Originally Posted by novicius View Post
Well this is an engineering issue -- assume that said theoretical Quiet Gun is fully engineered to work with subsonic ammunition vs repurposing an existing weapon system.
For pistols it can be as easy as changing a spring that gets pulled out every time you clean it. However, few manufacturers are going to sell pistols from the factory set up specifically that way so long as you have to pay a $200 tax on top of the suppressor and wait several months for ATF approval. Per suppressor. Ironically, despite stiffer regulations on acquiring firearms, suppressors are usually much easier to acquire in European countries.

Quote Originally Posted by novicius View Post
Would a slower, bigger bullet have these issues? Bullet design is as critical as the gun it's fired from, right? #assumptions
Slow bullets may still have these issues. Non-hollow point 45 ACP will shoot straight through people, and non-hollow point 9mm will as well. Bullet design in the form of expanding/fragmenting rounds is the solution. However, nothing is 100% in the real world. The old 147 gr 9mm rounds I cited worked fine in ballistic gel tests from full size test barrels. Throw in real world variables like heavier clothing than was used in the test along with shorter barrels or looser chambers reducing velocity, and you can get hollow points falling to expand. Hollow point design is tricky. Usually there's an optimum velocity range. If the bullet gets pushed too fast via a longer barrel or hotter than factory handloads, the bullet expands but the petals get pushed back, which can result in a smaller bullet than over penetrates. If the bullet is too slow, the hollow point will fail to expand and be more likely to zip right through people.