Why would General Polk need this gun?

Consider this receipt from Tredegar dated October 17, 1861.

The last itemized line in the receipt is “1 – 8in rifle gun” at a cost of $9500. The document further stipulates the gun was intended for General Leonidas Polk in Memphis Tennessee.  The first waypoint on that trip was the Richmond & Danville Railroad depot.

So why would General Polk need such a large rifled gun way out in the western theater at this early stage of the war?

And more directly to the topic of my blog, what design did Tredegar use for this large caliber rifled gun?  Prior to the Civil War tests of large caliber guns (smoothbore and rifled) had met with only limited success.  So what designs did Tredegar borrow from?

First correct answer to these questions wins…. well… wins….