They're highly regulated and can be used in WA but only with special permit for use by Dept of Ag staff. Not sure when they were used last or if they're used regularly but they do currently have an application.
The science behind them is quite simple, they're a tube with baffles just like a car's muffler, they take the "crack" of the projectile breaking the sonic barrier and its this effect that washes part of the noise off the firing.
They don't as Hollywood would have you believe "Silence" a gun shot.
The upside is they can allow a firearm to be fired without the user wearing hearing protection and in most cases it reduces the shot feedback to below 140dB which is lessens chances of damage to people's hearing. This means in things when doing things like scrub hunting for pigs a person can have full hearing available to them & stay safer. Not overly common but if a hunter comes across a big boar and startles them, they can attack.
In the case of target shooting many shooters won't want to use them in some disciplines but some competitions in some areas will like to use them. But there are negatives.
Precision and accuracy in shooting is actually consistency. A suppressor does have a minor effect on consistency. They do need maintenance, they need to be clean regularly and with every shot fired in succession the suppressor tube will heat up.
Even with a clean, cold suppressor because a suppressor interferes with the gas shock it affects the projectile's ballistics. It will reduce muzzle velocity so if precision is required then yes all the ballistic charts you have for a particular round will have to be retested so your "firing solution" (adjusting scope for bullet drop) has to be recalculated and with some rounds a scope zero will differ from a non suppressed zero point.
For the longer shots it make also have a minor effective on the energy delivered to the target but probably not enough to make much difference in a humane shot.
So they do have a place, they do have health & safety advantages, they do have limitations and some issues. They do have maintenance requirements and they do have to be fitted properly to avoid "baffle hit" which can be dangerous although rare.
They work best on closed chamber firearms such as bolt or lever action firearms. They work quite well on semi auto matic firearms but despite what some early Bond movies show, suppressors don't work on revolvers. Revolvers have a gap between the cylinder and the barrels forcing cone. Gas and noise escapes through this gap and as a result suppressors have little reasonable effect.
They may have applications with some disciplines in pistol target shooting allowing for easy to hear instructions from Range Officers. When hunting even a highly suppressed gun shot is loud, easily distinguishable as a gun shot. There is no added concealment and the prime advantage is no hearing protection required for most calibres. Most bullets go super sonic so it is not possible to make them go silent, you cannot beat the Physics.
So yes they have sensible and valuable applications and uses for firearms users but the likelihood of them being legalised is relatively small due to the unfairly demonised nature of firearms generally.
In New Zealand they are 100% legal, many hunters use them on even on the bigger hotter calibres just to keep noise shock down. They haven't presented any elevated threat to the community and not considered an issue at all.
WA though? Who knows. Sad part is there's plenty of YouTube videos showing how to make one at home. This sadly can be dangerous if not made & fitted properly but thankfully law abiding shooters don't go down that illegal path because being caught with one will cost you a criminal record, penalties and loss of firearms licence.
It might change, but pushes for or against must be practical and science based...not emotive Hollywood guided.
