• place AMV-7 Marshall with crew in editor
• as commander, enable manual fire to see what armament/ammo type is default

(default in AMV-7 Marshall is GPR-T 40 mm, then comes APFSDS-T 40 mm and Coaxial MG 7.62 mm)

• cancel manual fire
• press CTRL+F to order the gunner to switch to next available armament/ammo type
• in the chat, you see you ordered him to switch to APFSDS-T
• enable manual fire
• it's still GPR-T
• cancel manual fire
• order the gunner again via CTRL+F to switch to next available armament/ammo type
• it orders the AI gunner once again to switch to current APFSDS-T (still GPR-T), instead of switching to next available armament/ammo type

(you need to press CTRL+F twice so it cycles to Coaxial MG 7.62 mm)

• cycle via CTRL+F through all available armament/ammo type until you see the order for AI gunner to switch to GPR-T
• switch to manual fire
• it's now the opposite, it's actually APFSDS-T, despite the order saying it's GPR-T

So when you enable manual fire, you can without problems, with only one F click, switch from default GPR-T to APFSDS-T and also switch to APFSDS-T, without switching from GPR-T directly to Coaxial MG 7.62 mm.