Omega Strike
24 Achievements
Steam
Boomstick
Buy a weapon upgrade
48.2%
How to unlock the Boomstick achievement in Omega Strike - Definitive Guide
In the hub town of Tumbleweed, you'll find a NPC with an eyepatch called Snake. He will sell all the weapon upgrades in the game. I believe the cheapest upgrade you can buy from the start is the Rifle range upgrade for Sarge, at 50 gold. Simply buy it and this will pop.
At the hub area of Tumbleweed, there is a guy with an eye patch toward the right side of town. Talking to him allows you to buy weapon upgrades. Buying your first one unlocks this, but you'll likely end up buying most, if not all, by the time you finish the game. You'll likely have enough for a weapon upgrade by the time you reach the town for your first time.