Need some help with model #s

hi everyone, been eying a PTR91 for a long time but am confused about which one would be best for me.

i’m not looking for a precision rifle or anything too over the top. don’t plan on changing handguards or rails, just wanna shoot paper.

looking over atlantic firearms i see a few different GI models, including K models which have a shorter barrel.

can someone go over the different GI models vs the A3S

thanks i appreciate it