Does a handgun need to be fitted for a silencer or a barral rifled or machined or what?

Depends on what type of silencer you're talking about. If you're talking about the types you see on the end of an MP-5 used by special forces, this is threaded (also it severely decreases accuracy which is why it is only used in CQB. You can make a pretty good silencer with a milk jug, done right.

Any firearm can be equipped with a silencer. The easiest ones to attach silencers to are those with barrels that are unobstructed by magazine tubes, sights or double barrels. Most barrels are threaded to attach silencers. Some silencers attach with interrupted threads, or special adaptors. Most revolvers are not suitable due to the gap between the barrel and cylinder. The 1895 Nagant seals the gap with a cylinder that moves forward when ****** and brass that is longer than the cylinder and enters the back of the barrel. Some custom made revolvers have a very small gap to reduce noise, but they heat up ad bind after a short time shooting. Semi-auto rifles and pistols also have action noise that can be nearly as loud as the suppressed muzzle blast. Shotguns can be suppressed, but if shot shells are used, then the silencer bore has to be made larger to prevent the shot cup from catching on the internals as it opens. Instead of using a larger bore, a perforated cylinder can be used inside of the silencer tube to keep the shot cup closed. Either method reduces the effectiveness of the silencer as compared to rifle silencers. Another noise source is bullet flight noise. A bullet hitting a firm or hard target makes a loud whacking noise. Even subsonic bullets can make a humming noise as they fly through the air. Supersonic bullets (faster than 1100 fps) make a much louder whip cracking noise as they break the speed of sound. Machine guns are suitable for use with a silencer, but rapid fire makes the silencer heat up quickly. While making a machine gun silencer is practical as long as durable materials like steel, titanium and inconel are used, the barrel can heat up faster when shot suppressed. A good silencer will reduce muzzle blast noise by 20-30 decibels. This is a factor of 100 to 1000 times less noise. But even the small 22 caliber rim fire rifles are likely to be at least 115 decibels. The noise limit for safely shooting is 140 decibels. Even high powered rifles can be reduced to less than 140 decibels. Attaching a silencer to a rifle makes it much more enjoyable to shoot in my opinion. Ranb

The barrel would need to be threaded in most cases. A few manufacturers have started making barrels with a type of quick connect on the end where an "accessory" just snaps on. Keep in mind that a silencer can only be used effectively on firearms with stationary or lateral motion barrels. Something like a Glock, on the other hand, tilts the barrel when it cycles, so a traditional silencer setup would impede function of the gun.

Mark, Silencers are NOT Illegal. You just have to jump through a few hoops to get one, and contrary to other popular rumors you also do not need a Class III FFL to buy one either.

It will need the barrel threaded.

Handgun barrels are already rifled, but they need threading to allow the silencer to be screwed on.

They are also illegal in all 50 states.