Mowing the lawn.
I may be wrong and I don’t have a cite for it, but I understood that “blew his wad” came from “shot his wad”, thich came from black powder, muzzle loaded firearms and cannons. The term “wad” refers to the wadding that goes between the powder and the ball.
For example, if a duelist shot first and missed, he had “shot his wad” and was at the mercy of the other duelist.
However, all of this may have only existed in my head. No doubt, the usage has taken on a sexual conotation nowadays.
Three actual towns in Pennsylvania: The road from Blue Ball to Paradise runs through Intercourse.
I searched on “origin shoot your wad” and one of the first results was an old SDMB thread - I love the Dope!
In short - it looks like you’re right! It is likely more of an ammunition reference that later came to be considered a slang for ejaculation. Ignorance fought!
If you know what I mean…
Shelly Berman once wrote a book, first published in 1966, called Cleans & Dirtys, in which he explored this concept in some depth, like:
A fast move is a clean
A quickie is a dirty
A slicer is a clean
A hooker is a dirty
Tarzan walking with Jane is a clean
Tarzan swinging with Jane is a dirty.
Henry is a clean
Clyde is a dirty
Kiss whom? is a clean
Kiss what? is a dirty
Did you go to the Y and swim? is a clean
Did you go to the A & P? is a dirty
Giggle is a clean
Titter is a dirty
Shelly even explores “clirty”, which is “a cleaned up dirty, but since it began as a dirty, it can never attain the rank of clean.”
Hell is a dirty
Heck is a clirty
To pass a lake is a clean, But…To pass water is not a clirty, but a dirty.
…and there’s more, so go buy the book on Amazon.
From the SimCity series, when it is generating the world, a female (and to my ear, sexy) voice says, “Reticulating Splines.”
That was the appellation for a poster here once, wasn’t it?
In the bike shop the other day, the cashier confirmed his orientation by saying to the bloke on the shop floor: “I need you in front” 
I have to go water my succulents.
Hmm…how about Tickling Your Uvula?
Exit 664 on I-5 used to have a sign reading Balls Ferry. Google Earth doesn’t show it now, although it does show Balls Ferry Road nearby. Yes, it’s childish, but I was usually tired enough by the time I reached it to giggle.
Trimming the hedge.
Shucking the clams.
Steam cleaning the carpet.
When your yeast flocculates, it’s time to rack.
Beat me to it.
Moby Dick…is not a venereal disease and neither is Grape Nuts Flakes.
My favorite from this book:
A napkin that is dirty is clean.
A napkin that is sanitary is dirty.
Spock had such a dirty mind!
From my guitar and mandolin experience, “Changing my G-string.”
Shut the Front Door!