The difference between the targets for sighting in has more to do with the difference between sight separation of rifle and carbine than it does with barrel length.

OK, a minute of angle is 1.047 in at 100 yards. At 25 yards, 0.26 in. [That 0.047 in can add up big time way out there.]

Rifle with A2 sights: front sight, 1.25 MOA elevation per click; rear sight 1/2 MOA windage per click/1 MOA elevation per click.

Carbine with A2 sights: front sight, 1.875 MOA elevation per click; rear sight 3/4 MOA windage per click/ 1.5 MOA elevation per click.

If your rifle has A1 type sights the rifle version has 1 MOA per click adjustments for both windage and elevation. The carbine version has 1.5 MOA adjustments for both windage and elevation.