Pistol caliber ARs: floating firing pin or spring?

[Elkins45]

I sold my 9mm AR and I don’t remember. Does a pistol caliber AR use a floating firing pin like a standard rifle or is there some provision like a spring to reduce the chance of a slam fire with softer pistol primers?

 

[Cemetery21]

Made me look. Spring loaded.

 

[berettaprofessor]

My FM-9 has a spring.

 

[Elkins45]

Thanks for the replies.