Isn't a chronograph invaluable?
Using muzzle velocity measured by a chronograph, one can use any number of ballistic calculators available to purchase, or available on line, to calculate how one's bullet will fly. One can calculate where a bullet will hit a way out there, if one knows the muzzle velocity of the bullet. Myself, i have been able to kill deer a way over 200 yards out. Once, i killed an antelope (pronghorn), over 300 yards out with my muzzle loader. Shots like these are impossible, unless one has plenty of practice at range. Myself, i can't picture making these shots at ranges one doesn't practice, without knowing the muzzle velocity of one's load, unless one has a jillion tries. Naturally, it doesn't hurt to practice long range shooting at the range. However, at the range, one shoots at 100 yard, 200 yard, 300 yard etc. How does this insure point of impact at the in between ranges which naturally happen whilst hunting? Especially, especially using a muzzle loader at varying long ranges, it is very necessary to know muzzle velocity, which is found by using a chronograph.
Once, i smucked a milk jug filled with water at over 1/4 mile, using a muzzle loading rifle loaded with 115g of powder. This was done with one shot,........ one shot. There was no practice, there was no fire for affect (effect)? It seems the only only way a shot like this can be done, is by knowing the muzzle velocity, knowing the ballistic coefficient of the bullet, and using a ballistic calculator.
Sabots, as other mentioned, can/will/do damage one's chrono, and it is prudent to protect against sabot damage. Another issue i have experienced is placing the clock too close. This cures the issue of sabot separation, but allows muzzle blast to damage the machine.
Using a chronograph does require some simple precautions. Clocking in direct sun light should be avoided if possible. The machine needs to be placed close enough to avoid sabot damage, but far away enough to avoid 'blast' damage. Another way to clock bullet speed, is to put the 'clock' so far away, a sabot can't possibly reach it. This method requires one to use a ballistic calculator backwards, to find the muzzle velocity. One needs to develop simple skills in order to successfully measure bullet speed.