Depends upon what the law says.
http://www.oscn.net/applications/oscn/DeliverDocument.asp?CiteID=69785
As used in Sections 1 through 25 of this act:
1. "Concealed handgun" means a loaded or unloaded pistol carried hidden from the detection and view of another person either upon or about the person, in a purse or other container belonging to the person, or in a vehicle which is operated by the person or in which the person is riding as a passenger; and
2. "Pistol" means any derringer, revolver or semiautomatic firearm which:
a. has an overall length of less than sixteen (16) inches and is able to be fully concealed from detection and view,
b. is capable of discharging a projectile composed of any material which may reasonably be expected to be able to cause lethal injury,
c. is designed to be held and fired by the use of a single hand, and
d. uses either gunpowder, gas or any means of rocket propulsion to discharge the projectile. The definition of pistol for purposes of the Oklahoma Self-Defense Act shall not apply to homemade or imitation pistols, flare guns, underwater fishing guns or blank pistols.
There is also this, although it probably doesn't apply to the AR 15 pistol, depending upon the ammunition.
http://www.oscn.net/applications/oscn/DeliverDocument.asp?CiteID=69789
Any concealed handgun when carried in a manner authorized by the provisions of the Oklahoma Self-Defense Act, Sections 1 through 25 of this act, when loaded with any ammunition which is either a restricted bullet as defined by Section 1289.19 of Title 21 of the Oklahoma Statutes or is larger than .45 caliber or is otherwise prohibited by law shall be deemed a prohibited weapon for purposes of the Oklahoma Self-Defense Act. Any person violating the provisions of this section shall be punished for a criminal offense as provided by Section 1272 of Title 21 of the Oklahoma Statutes or any other applicable provision of law. In addition to any criminal prosecution for a violation of the provisions of this section, the licensee shall be subject to an administrative fine of Five Hundred Dollars ($500.00), upon a hearing and determination by the Oklahoma State Bureau of Investigation that the person is in violation of the provisions of this section.
Good reminder info thanks. So I take it that legally you could carry one in your car. Shorter than 16'' smaller than a .45 cal.