Actually, yes there will be a way to do it.

For one thing, the crossbow-mastery feat allows you to IGNORE the loading property of crossbows, so you can indeed use a shield.

Not to mention that a sensible artificer would be using the Repeating Shot infusion with their crossbow.

While it is ambiguous whether the lightning launcher is "one-handed", it most definitely is not two-handed and thus there would also be a good argument for using the crossbow afterwards not as part of the mastery feat but as two-weapon fighting (in which case you can no-longer add your dex-score the the damage)

So have a word with your DM, and ask which way you should be working-it.

Actually, yes there will be a way to do it.

For one thing, the crossbow-mastery feat allows you to IGNORE the loading property of crossbows, so you can indeed use a shield.

Not to mention that a sensible artificer would be using the Repeating Shot infusion with their crossbow.

While it is ambiguous whether the lightning launcher is "one-handed", it most definitely is not two-handed and thus there would be a good argument for using the crossbow afterwards.

So have a word with your DM, and ask which way you should be working-it.