I believe only only 6 states and D.C. limit the capacity of magazines. State Regulations exist in California, Hawaii, Maryland, Massachusetts, New Jersey and New York.
Don't want the crime rates of those places!
Ohio has a limit of 30 rounds for magazines, before the magazine is treated in the same way a Class III weapon item is by state law and thus needs a special permit for use and possession in certain cases.
ORC 2923.11 Weapons control definitions.
As used in sections 2923.11 to 2923.24 of the Revised Code:
(A) “Deadly weapon” means any instrument, device, or thing capable of inflicting death, and designed or specially adapted for use as a weapon, or possessed, carried, or used as a weapon.
(B)(1) “Firearm” means any deadly weapon capable of expelling or propelling one or more projectiles by the action of an explosive or combustible propellant. “Firearm” includes an unloaded firearm, and any firearm that is inoperable but that can readily be rendered operable.
(2) When determining whether a firearm is capable of expelling or propelling one or more projectiles by the action of an explosive or combustible propellant, the trier of fact may rely upon circumstantial evidence, including, but not limited to, the representations and actions of the individual exercising control over the firearm.
(C) “Handgun” means any of the following:
(1) Any firearm that has a short stock and is designed to be held and fired by the use of a single hand;
(2) Any combination of parts from which a firearm of a type described in division (C)(1) of this section can be assembled.
(D) “Semi-automatic firearm” means any firearm designed or specially adapted to fire a single cartridge and automatically chamber a succeeding cartridge ready to fire, with a single function of the trigger.
(E) “Automatic firearm” means any firearm designed or specially adapted to fire a succession of cartridges with a single function of the trigger. “Automatic firearm” also means any semi-automatic firearm designed or specially adapted to fire more than thirty-one cartridges without reloading, other than a firearm chambering only .22 caliber short, long, or long-rifle cartridges.