Grooping question

[soundwaves]

ok so l cleened my rifle and went to the range. shot 1 round out of the cleen bore to mark a point of aim on the target. then fired a 3 shot groop from a 100 yards. the groop was tight about half an inch wich 2 bullets went through the saim hole.
then l fired a nother 4 shot groop but this groop seemed strange to me because the 4 shot groop was around an inch that had 2 bullets go through the saim and a nother on top and a nother on the bottom of them. so it was pretty much a vertical groop. it seemed strange to me to see a almost perfectly vertical groop line.
can something cause this vertical grooping ? l use factory ammo ( power-shock ) so l thought maybe the 2 rounds that landed high and low had diferent amount of powder than the 2 bullets that impacted in the saim hole there fore haveing diferent velocities ? l was shooting in to the wind so maybe it was the wind messing around ? hotter barrel than my first groop ? the ammo l used was about 5 years old thats why l went to the range to finish them off. maybe its that ?
just want to learn some things from some of you serious target shooters WHO know about there groops as l dont target shoot, l only hunt, only time l shoot groops is when sighting in my rifle

thanks in advance for the replies

 

[dok7mm]

1. Hotter barrel temperature
2. Differing powder charge in factory ammo.
3. Differing neck tension in factory ammo.
4. Slightly different bullet weight.
5. Shooter error.
6. Action needs torque change.

Probably more. Take your pick.

 

[Barrelnut]

Dok has a good list.

Here's a couple more.

1. If shooting from bags, not having the forearm in the same position for each shot.
2. If it's a carry weight hunting rifle, inconsistent check pressure on the stock or even inconsistent shoulder pressure or hand weight gripping the stock. Rifles that have some muzzle jump are real susceptible to this.