You never really know what velocity you are getting from your gun unless you measure it with a bullet chronograph. There are hundreds of variables that have an effect on muzzle velocity such as barrel length, action type, weather conditions, primer, powder, powder charge, bullet, brass, chamber dimensions, etc.
A bullet chronograph calculates the velocity by measuring the time it takes the bullet to pass over 2 screens. It’s very accurate and easy to use. The display shows you the velocity after each shot.
The Shooting Chrony F1 is a great bullet chronograph and very inexpensive. I have used one in the past and loved it. It’s really neat to see what velocities you are getting when handloading.