Two friends and I pretty much recreated this on KF-Stranded on Normal earlier.
All of us bought pipe bombs, I had four, one had three and the other had two ( he wasn't a demolitions ). Add to that the ones we liberally sprinkled around the field that survived the previous waves.
Patches tried to rush us, but he ran through the field long-ways and got pasted. I've never saw that happen to him before =o.
I also am into the habit of doing this myself while playing - I'll place all but one of my bombs, and walk around picking up loose ammo ( I'm alone so it doesn't matter ), and place more. On Waterworks, for example, the map was covered with the things by the time anyone joined and the wave consisted of half of the specimens blowing themselves up.
In fact, I was on Wyre and placed one where Patches ended up spawning that time, so there's all kinds of hilarious shenanigans that these can be used for.