A different version of the JM Model is the JMDB Model which is the only model in the world with a double barrel technique. The standard model of JMDB is delivered with 11mm and 13mm barrels. It is easy to interchange the 11mm barrel (for 1,5 and 3.0 ml darts) and the 13mm barrel (for 5.0 and 10.0 ml darts). The double barrel is also advantageous in the situation where one cannot choose the closing level until arriving at the location and seeing the specific situation. This model can also be delivered with two barrels of the same size.