Ever done this?

[JoeRaisin <joeraisin@xxxxxxxxxxx>]

So this is how my day went....

Installing a Vista 32-FB in a county building to monitor hte sprinkler
system (they have both wet and dry systems)
Got flex to all the flow and tamper boxes except one and am working on
the last...
First step, knock out the knock out on the back of the box - careful of
the 110 bell circuit already wired to one of the switches.
Put my punch on the perimeter of the knock out and tap with my
hammer...nothing...
Second tap and the box breaks off, the bell starts ringing and air
shoots out of whats left of the pipe (it was the low air alarm)
I put my finger over the hole to keep whats left of the air pressure
(now at just over 30 lbs) in the system until I can get the water shut
off (lesson learned there - shut it off FIRST)
The water valve is chained and no key in sight.  Bell ringing right over
my head but nobody seems to notice.  For at least 5 minutes I am
standing there under a ringing bell with my finger blocking the hole.  I
figure If the clapper releases I will then have water shooting out of a
1/4 inch hole with a lot more pressure than the air currently is.
Finally someone notices me and I send them looking for the key to the
chain holding the butterfly valve open.
No key can be found and it takes several more minutes before bolt
cutters can be found to cut the chain and shut off the water.
The sprinkler guys show up later and replace the switch.  The fella I
spoke with said he has never seen one do that before, but theyt have
recently started using plastic fittings to connect the tamper boxes to
the pipes.  (Plastic pipe, 3/4 od and 1/4 id)
We tapped out both knockouts BEFORE mounting the box this time....

Question: Anyone got a better way of getting rid of those knockouts?  I
thought of a 7/8 hole saw next time but not sure how well that may work
since they tend to get grabby and either twist off the box or slam my
drill (and hand) into something delicate or energized.

I would rather not go through this again....

BTW, I later found the key in the spinkler repair parts box next to the
wet risers on the other side of the building (which is the first place I
told them to look)