I recently bought a Glock G40 MOS 10mm, and since it’s the MOS version I wanted to put a red dot on it. I went with the Holosun 507c since I’ve had good luck with them in the past.
Took it to the range and bought several boxes of what they had for sale, at roughly 60c/round it seemed like a good deal! Lo and behold there was a reason it was so cheap. No matter the distance, shooting supported or offhand, I could not get a good enough group to get the dot zeroed. I went through something like 200 rounds and actually swapped the Holosun for one off of another pistol just in case that was the issue, before realizing it was probably an ammo issue. I took off the dot and went back to basics with the iron sights, got a new brand of ammo (the PMC in the pic below), ran a target out to 7 yards and shot 5 rounds of each ammo type.
I guess it wasn’t the dot that was the problem! At least I only have 400 rounds of this stuff left