Consumer: "Thanks but I've shot my wad on this subject." (I'm done, don't want to take it further.)
PS One hopes the provenance of this perhaps somewhat dated colloquialism was not an ugly sexual allusion to the male orgasm (back in the 50's when scumbag was an ugly slang term for condom) but at the time if it was, it did not seem to be generally thought of as such. But looking back, I dunno.
A musket is a muzzle-loaded, smoothbore firearm, fired from the shoulder. Muskets were designed for use by infantry.
A soldier armed with a musket had the designation "musketman" or "musketeer".
(When soldiers ran out of bullets, they would resort to "shooting their wad".)