"I got your gun !" OP says
"Not all of them!" Other guy
"BANG!"
In CT:
Sec. 53a-21. Use of physical force in defense of property. A person is justified in using reasonable physical force upon another person when and to the extent that he reasonably believes such to be necessary to prevent an attempt by such other person to commit larceny or criminal mischief involving property, or when and to the extent he reasonably believes such to be necessary to regain property which he reasonably believes to have been acquired by larceny within a reasonable time prior to the use of such force; but he may use deadly physical force under such circumstances only in defense of person as prescribed in section 53a-19.
In Washington
RCW 9A.16.050
Homicide—By other person—When justifiable.
Homicide is also justifiable when committed either:
(1) In the lawful defense of the slayer, or his or her husband, wife, parent, child, brother, or sister, or of any other person in his or her presence or company, when there is reasonable ground to apprehend a design on the part of the person slain to commit a felony or to do some great personal injury to the slayer or to any such person, and there is imminent danger of such design being accomplished; or
(2) In the actual resistance of an attempt to commit a felony upon the slayer, in his or her presence, or upon or in a dwelling, or other place of abode, in which he or she is.
Theft of a firearm is a felony under RCW 9A.56.300 deadly force is justified under RCW 9A.16.050 A(2)