https://www.pcgamer.com/pubg-unveils-sanhok-forty-fivers-event-mode-fixes-bullet-penetration/

PUBG's latest limited-time Event Mode enters its 4x4km Sanhok map. Named 'Sanhok Forty-Fivers', it's a four-person squad (80 players max) free-for-all whereby the only spawnable guns are compatible with blue-boxed .45 ammunition. 

Which means you're restricted to Tommy Guns, Win94s, R45s, P1911s, and, to mix things up a little, throwables. Care packages contain Vectors, 0.45 ACP rounds and Lvl 3 gear; and the safe zone starts small, and is visible from the outset. Weather is set to Overcast, red zones are disabled, and teamkilling is a no-no.