testing an old fieldstone well

I have an old fieldstone well that I would like to use for a sprinkler system. I know nothing about this wells yeild and after quite a bit of searching havnt found much on how to check. The well is about 2 feet wide and maybe 20 feet deep. The water level is maybe 12 feet down. I would have to remeasure though since it has been hot and dry so long... Anyway how do I figure out what kind of flow this well can support so that I can size a pump acordingly? Do I just rent a big gass powered pump, pump it dry and see how long it takes to fill back up? Most tests I have read about flow and pressure seem to quantify the pump and not the well. I would like to figure out what im dealing with before investing time money and effort into a well that wont do what Im looking for.

If this has already been covered please point me in the right dirrection because I cant find it anywhere.

Stick a 1/2 or 3/4 hp jet pump on it and let her rip.

So I pried the cement lid off the well tonight. 10'6" to water and 12'6" to the bottom. I found an old 1/4HP sump in the basement and hooked it to a 100' garden hose and it is putting out right around 5 GPM. It also is making no difference in the water level at all so I guess I will be needing a bigger pump for testing purposes...
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Never mind, spoke too soon, im down 4" so far.
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Goinng to go check again now... yea im down almost a foot now. I guess Ill just keep going untill im about out of water and see how fast it fills up. I guess if I can drain the well at 5 GPM its not all that fast a well huh...
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Ok so I have pumped the well down within a couple inches of the bottom. 12'4" to water, and im going to see how it does refilling...
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Time since removing pump => distance to water
Time = 0:00 => 12'4"
Time = 0:30 => 12'2"
Time = 1:00 => 11'11"
Time = 1:30 => 11'9"
Time = 2:00 => 11'7"
Time = 2:30 => 11'6"
Time = 9:30 => 10'8"

Now restrict the flow out and see what GPM it stabilizes at. You might bail out some of the muck at the bottom and deepen the pit.

I checked this morning. 9:30 hours after removing the pump and im back up to 10'8" to water. I thought about restricting the pump and trying to find a steady state, I also roughly calculated how many gallons seem to be refilling the well per hour. Looks like somwhere in the ballpark of 20 gallons per hour. Assuming the well is 3' in diameter at the bottom which is a bit wider than the top, not sure why that is. But anyway I assume that I am not putting in a sprinkler system with somwhere around 500 gallons/day. Mucking out the bottom might still not be a bad idea. This well was used at one time a long time ago, there is an old lead pipe coming from the dirrection of the house, entering the well a couple feet down and running down into the water.

You might try driving a point right down the center.

I thought of that, and you never know unless you try, but I cringe to think about driving anything down through the ground around me. Fieldstone everywhere! I might give it a shot this weekend but I think my chances of not hitting a rock are probably pretty slim. Still might not be a bad weekend project.

test the ground with a piece of steel pipehooked up to a hose and try jetting down, see if you can find a clean spot.