US Concealed Weapons Laws
I have a NY State concelaed weapons permit and am also a former NYS municipal police commissioner. Sadly, like our country's liquor laws, there are fifty different laws on the books regarding the carrying of concealed weapons, with New Jersey and Massachusetts being at one end of the spectrum and Texas and Montana being at the other end. When you go to google and type in concealed weapons carry or words to that effect, you see many websites devoted to this topic. The bottom line is that in States with strict gun laws, those States generally fail to recognise any other States carry laws. Thus NY's carry permit is not recognised by any other State since NY refuses to recognise any other States; ergo, there is no quid pro quo. However, a Texas or Florida carry permit is recognised by 18 other States.
If you use a weapon in any State with reasonably strict carry laws, the subsequent police inquiry must show that A.) A rational person would have felt their life was in extreme peril if they were in your position when you made the decision to draw and fire your weapon; and that B.) If circumstances permitted, you gave the attacker warning before shooting him or her. Massachusetts goes to the extreme of stating you must have retreated to point where you had no where else to go before employing deadly force. This ruling came down when a female shot a burgler through her bedroom door rather than retreating into her bathroom - the furthest point she could have retreated to.
Hope this helps a little. Shane