Wallbang guide
What the game files say about each round passing through cover, side by side.
Unconfirmed. The files give each round a share of speed kept after it passes through a surface. A few rounds also have a penetration strength. We have not tested how these play out in game yet (the .50 keeps the least speed but has the highest strength, for example), so it is part of our range test list.
Speed kept is the game file's exit speed multiplier: the share of a bullet's speed left after it passes through a surface. Exit speed uses the fastest gun firing that round. Some rounds also carry a penetration strength multiplier, shown where the files give one. How thick a wall each round beats depends on the surface's material, which the files keep with the map, so test the specifics in game.