I've noticed something strange about my regular shooters. My AR, AK, FAL, and Garand all have their rear sight windage adjusted to the left when I zeroed them all. The distance they were adjusted is roughly equal between them all, but they all are zeroed now. I just thought it was weird that all four rifles were adjusted to the left, and all four rifles have different sight styles. I'm thinking I'm the reason they're having to be adjusted to the left. Would changing the way I shoot fix it? When I sighted all of the above rifles in they were supported off of an ammo can if that helps anything.
Since I have them zeroed, it's not a big deal, I'd just like to get the windage adjustment as centered as possible.

Noob here

I pull left on my handguns and especially my ar.

I think i am pulling with my non trigger hand.

My sniper friend said to put a quarter on the barrel and practice dry firing without losing the quarter

I have had some surgery on my neck and can't move my head like I once did....on glass and irons I have everything cranked about as far as it will go to the left.

I have thought about adjustable rings but just never went to it....but I know I need to.

It's you...........and what's it matter if they are zeroed?   I think military manuals say within 15 clicks either way is normal........may possibly be 20

Astigmatism?

Adjustable sights are on guns because not everyone is the same. Some people pull left and others pull right. Some pull high and some pull low. 

It would be interesting if it's a coincidence.  Seems like too many to be a coincidence.  But who knows....... I have very few guns that zero exactly right down the middle.  I know of at least one that does.  Now you're going to have me checking them all.     My M4gery goes right down the middle, and my recce is usually 4 to the left.  But I'm pretty sure it's cuz the front sight is on a rail (when I have the irons on it).  

I'll start double checking my other guns.