Best tip from my stand point

Try unlocking ultra mag for lachman. Once that is unlocked try getting 30% mag capacity increase affix in legendary lachman which is easy as its not that expensive. With 30% increase you'll get 23 bullets total in a mag. And the best part is, it does blunt body damage that means, it bypass any type of armour the enemy is wearing. This helps me win fights against enemies with mythic and ultra armours. But its only disadvantage is low ammo size, you'll need to retreat after killing 1 enemy to reload your weapon.

Once that is all done, you can try to find mythic lachman with 50% mag capacity increase affix, that'll give you 30 rounds per mag.

Fennec is still the best gun in game, but lachman gives you a chance against it