Sighting in a thermal scope is a little different than a daytime optic. You will need a special target and an understanding of how to follow the bullet impact. Once you sight one in successfully, it will become second nature.
There are a lot of tricks to making a target for a thermal scope but I will talk about the easiest. First, you will need a 2’ X 1’ 4” honeycomb sign you can find on the side of the road or your local home improvement/ office supply store. Second, you will need a 2” X 4” heating pad. Once you have these materials, tape the heating pad to the center of the honeycomb sign. For a more accurate zero, fold the heating pad in half.
If you read the manual you will see that most of the boresight corrections are based off 100m. I like to sight my rifles in at 50 yards and compensate for bullet rise and drop. At 50y the bullet will be about 2” low and on the money at 175 yards. The reason behind this is normally my first shot on a group of hogs will be within 50 yards. The running shots will be between 50 and 175 yards so I know I will be on my first pig and still be able to hit pigs on the run because the bullet is rising and dropping in the kill zone. We only shoot 180g .308 so if you are shooting a .223, you will want the bullet impact only 1” low at 50 yards because it is a flatter shooting round.
I am shooting the FLIR Thermosight RX Pro 640 50mm on a Daniel Defense DD5V1. The gun is sitting on Primos shooting sticks with the target at 50 yards. I took this scope off of my personal gun and mounted it on another to sight it in. I shot twice at the heating pad. My group was 6” high and 5” left. At 50 yards one click is almost 1”. I hold down the center button to reach the main menu; scroll down to Boresight; adjust the windage 6 clicks left and elevation 8 clicks up. I hold down the center button until I see the reticle jump up and to the left. I exit the menu and shoot two more times. This time my elevation is perfect but I pulled one shot to the right. I go back into the boresight and adjust the windage one click left and shoot two more times. This is exactly where I want my bullet impact. I always wright down my X and Y numbers in the boresight menu so if I ever switch guns again, I will be able to input the numbers and be very close to zero.
1st two shots 6″ high and 5″ left
Adjusted X= -6, Y= 8
Adjusted X= -1
You can also watch this video that will show you step by step: Zeroing the Armasight Zeus