Very nice Vietnammarine! Always you pleasure to see one of these trenchguns, they're a rare sight nowadays
I like the Madbull shells a lot, they're very high quality, completely made of metal and easier to fill with gas, as they have a fixed valve on the side instead of the bottom, where the valve also fills the role of gas release point.
However, their metal construction also makes them heavier, so I reckon they'd not just "bounce off" the ground, it might be possible that they'd take more damage falling onto concrete for example. Using this gun in a game would be high risk and you