Bushnell radar gun always displays the same speed

When radar detectors proved easily capable of sniffing out radar from miles away, radar gun manufacturers responded by producing instant-on radar or unoffically called "Pulse" radar. In the instant-on mode, the radar's transmitter is placed on hold, ready to fire but not yet producing a signal for detectors to hear. The officer waits until his target is very close (brings a new meaning to "wait till you see the whites of their eyes") then releases the radar from stand by mode and gets a speed reading within a second or so (pulse). In this situation, no detector offers much warning.
There are guns out there that operate just like the instant-on guns of the past but with a very tough twist - POPTM mode! This gun is a normal K and Ka band radar gun detectable by most radar detectors made in the past 30 years, until this gun is placed in POP mode. When the gun is in POP™ Mode and activated, a brief burst of energy, less than 1/15 of a second, is transmitted and the vehicle's speed is quickly acquired. A detector without POP™ Mode detection capability cannot respond to this brief transmission.
TIP - When traveling in unfamiliar highways always try to find a vehicle which is traveling at the same rate or faster than you are and keep several car lengths behind them. This way the other vehicle can "flush out the radar".

Have you tryed to point it at a car which is going faster than 20 mph?

You can add up to 25 miles an hour and more to your swing speed by taking advantage of your hidden, built-in swing speed multiplier. The top pros have always taken advantage of their hidden swing speed multiplier. It's why they drive the ball 280-300 yards The average golfer does not know he has a swing speed multiplier built into his own body-and drives the ball 210-220.

What is the swing speed multiplier built into every golfer? And how does it affect swing speed? It is a hidden lever system that multiplies any increase in hip speed 25 times.

it is a abbreviation for Radio detection and ranging.
In principle there is a transmitter and a receiver. When the transmitter sends a signal at time zero, the radio waves will move away with the speed of light. When the waves bounce against an object a part of the radio energy comes back. When the retiring energy comes in the receiver, and you did measure the time, you can calculate the distance to the object.

if you also know the angle of the antenna you can plot that point in space. if the object moves and you get several measurements, you also can calculate its speed.

That is what the police likes to do, to catch speeding motorists.

A laser gun works on the same principle, but the radio waves are changed to light comping from a laser.

yes you need to hold the trigger down as it passes by

Yes. On many radar gun models the officer can lock your speed and turn the radar gun off, yet the radar gun will still display the locked speed. Officers are not required to show you the locked speed.