| Numarak |
To consider that any possible weapon is able to fit in a sccabard would be stretching the rules; there are other instances for 'sccabard' on the game, and most of them refer to blade like weapons.
When we do not have a specific rule, we have to use English definitions.
After reading it, I would consider possible to have a sccabard for a rifle, not so sure about a musket, since muskets' cannon's extreme usually was wider than rifle's ones.
So, RAW arguable, RAI I would fall for a 'no'.