I take the plastic ammo belts provided with the kits (Dragon/DML and sometimes Tamiya) and cut them into 1- to 4-round (bullet) sections, then glue the sections back together in the manner I like. I usually cut from the original belt as I work, that way I know how many rounds to separate for the next portion. Sometimes I use a very thin wire or strip of masking tape to provide a backing for the ammo belt and something extra for the little sections and glue to adhere.
I am working on a Hanomag dio and have a gunner manning the MG 42 on the top. I used this method to drape the belt over his left hand helping to feed the belt into the weapon.
[WARNING: this method requires a great deal of patience and small amounts of super glue.]
Remember, the MG 34 and 42 used a reusable linking system that stayed intact after going through the weapon. I scratchbuilt this by taking a thin strip of masking tape folded over on itself (no adhesive on the outside), then crimping it in a pair of serated surgical forceps. Then carefully, remove the tape, coat it with super glue and let dry. You may need to re-crimp after the glue dries, but paint and weather as desired. It's a great effect!