There is an omod included in the Gyrojet ammo plugin that you are recommended to put into your weapon template for weapons that use the gyrojet ammo. This sets the out of range damage multiplier to positive 2 which will actually make it do more damage once the max range of the weapon firing the Gyrojet round is exceeded.

If you are using Gyrojet for an ammo conversion modification then simply paste the stats from the included omod into your ammo conversion modification. This is just a single property that does as explained.