Far Cry New Dawn - Easy Space Force SA-50 Upgrades
This is the fastest and easiest method that I have found to upgrade the damage for the SA-50. You will eventually need to grab some other resources, but this works well in occasional bursts between Outposts and Expeditions, and also a break from mission fatigue.
It is important to use Timber, as he distracts the prey and also to fast travel to Prosperity, as this replenishes the Yucca, an ingredient for bait. You can repeat this process as the Monstrous Bison re-spawns quickly.