Khador gun carriage on charge

It's a cavalry model, so it gets a boosted attack roll against its charge target and can make impact attacks (not boosted) against one or more models if it contacts one during the charge. This can only be done once, and if you fail to clear the path to your charge target, your charge will fail.
The mount weapon slams any models hit, so that should work on impact attacks that hit.
The mount weapon is also usable as your charge weapon (not usually true for cavalry), so you can charge with the mount and then make your ranged initials.
As usual, if you choose to make an impact attack against your charge target and kill it or slam it out of range, you can make your charge attack against another model in range, but the damage roll won't be boosted.

That seems to cover the typical cases, do you have more specific questions?