A replacement muffler which can replace original equipment mufflers with substantially no modifications thereto, and methods for producing the same are disclosed. The replacement muffler is provided with a muffler body which only approximates the body of the original equipment muffler and a pair of replacement muffler nipples secured to the muffler body, having diameters substantially equal to the corresponding nipple diameters of the original equipment muffler and having lengths adapted to produce a nipple-to-nipple length substantially equal to the corresponding length of the original equipment muffler. The replacement muffler may be produced with a six to seven fold increase in production line efficiency by customizing only the nipple portions of the replacement muffler.