Mont. Code Ann. § 25-30-104
25-30-104 Reply to counterclaim or new matter
25-30-104 . Reply to counterclaim or new matter. Whenever the answer contains a counterclaim or any new matter, the plaintiff shall within 5 days after the service and filing of the answer reply to the counterclaim or new matter in the manner and form provided for in Rules 7(a), 8(d)(2) and (d)(3), and 10(b), M.R.Civ.P.