There's no mention of it in the book, except that Chaos Renegade Militias' lasguns have it.

So do lasguns have it or no?

You always have the choice to make a new setting for any of your games, or port one game into another setting, it's just that the Beta doesn't come with any real amount of fluff.

He's referring to the variable setting rule for lasguns in Black Crusade. These rules persist in Only War, but ONLY in regards to the Triplex Pattern.