When using the ladder method of load development, it is crucial that all the shots are shot in quick succession, during the same session. This is done, to ensure similar environmental and other changing conditions for all the shots, in order to obtain a consistent result and accurate difference. The other problem with this, is that for the ladder method to work effectively, you need to ensure that the hole on the target is matched to the correct charge load cartridge that was shot, so as to know which ones provided you the desired result.
This sounds simple enough, except for the fact that you are 300 yards away from your target, so it is not practical to run 600m between each of the 12 or more shots and mark each one.
The old method we used to do, was having someone else hide behind a gravel mount or wall, downrange close to the target with a two-way radio, and the shooter would clear the rifle after each shot, radio the other person to go to the target and mark the shot, and then chamber and shoot the next round as soon as that person downrange is safely hidden again. This can still work, but only if you have a buddy with you, and if you have a two-day radio.
Nowadays, it is much easier with the advent of technology, and we use the Longshot target cameras, which makes it much quicker and easier, and you get real-time feedback right next to you as you shoot on your tablet or smartphone screen, and you can mark each shot and keep the marked image of the target for later use and reference.
Not only for ladder test load development, but even for long range target shooting to check you hits, or to true your DOPE, the top of the range model has a 2 mile reach, truly remarkable.
It is a purpose built camera that connects with Wi Fi to your phone or tablet so you can see your target and shots on it and can tag every shot on your phone or tablet screen. It saves a lot of time and allows you to shoot the ladder effectively before the conditions change. With this camera you can shoot multiple guns during the same session with a ladder test.
When you use the link above to shop for one of the products, we receive a small commission from the sale, at no extra cost to you. This helps us keep this site going, and does not affect the price you would pay usually in any way whatsoever.
This image is one where I tagged the shots on my phone, so excuse the low smartphone image quality, it is much better on newer smartphones and tablets.

I just use a ShotMarker, it labels the shots sequentially. Easy peezy.