Historically just Americans used 50bmg for AA. Others used 20mm and larger, because they can load explosive in the projectile. Drones make sense to repurpose to a smaller cartridge.
50bmg is very underrated. It’s the largest gun you can buy without an NFA stamp. The ammo is cheap compared to other high energy rifles. The m2a1 is one of the longest serving machine guns. Buy one while you still can
Yup, with shahed drones the important part is shooting them down as cheaply as possible. They're cheap and relatively small. But are made in large numbers (~500 drones in total were used last night, though even cheaper decoy drones are a part of that # too). So you have to be able to defeat them on a budget. Hence the use of relatively cheap 50 BMG, often just mounted on the back of relatively cheap pickup trucks.
Unfortunately, for various reasons they are becoming harder to shoot down with standard guns as Russia is finding ways to fly them at much higher altitudes, only diving to the ground at the last minute. My understanding is that Ukrainian aa defense is increasingly using anti-drone-drones to combat this.
