I have been picking Americans for a while now, and it took me weeks before I could even open one. I still cannot open one that a friend of mine has. I tried the WD-40 and it does help! But I let it dry out overnight before I picked it... I have picked these wet with WD as well, so I would say to try it both ways.
What I have noticed is that all the American brand padlocks that I own seem to have at least one deep cut/long pin... This may or may not help you, but I figured I would mention it anyway. If the pins seem to be binding then maybe it is just the serrations messing with you! I had that same prob and found that tapping the pins and bouncing the wrench a little would give me a click or 2. but if not, I would move on to the next pin and try it again. If the plug moves at the same time, then it's prolly a spool or three.
I don't see why an electric pick gun would not work on these since I have seen one opened with a snap gun... the electric guns just use vibration to do the same thing from what I understand. (The pool ball effect, hehe) So if you get/make an electric gun please let everyone know the results! I probably won't come across an electric gun myself, but if I do then I will certainly try this out and let the whole world know
anyway, if you still wanna pick it......
I have a 5100, 5200, a series 40 and have also picked a series 20. My homemade tension tool doesn't fit all that well, so it's a real pain. These locks pick better with a solid fit, not necesarily tight, but you need some feedback even though most of the clicks are serrations which all of mine have. You need to be able to feel the difference between the serrations and when the plug breaks loose. It is really subtle. When I hear a click and I am not sure (or have been picking it for days) I will try to give it a push to see if it gives just in case. Also, I have a 5100 that kinda sticks a bit when I try to rotate the plug after it has been picked. I had a problem with the tension wrench binding as well that killed all feedback. Make sure your tension tool is not binding at all! very important.. I have sat and picked at one of these for like an hour only to discover that I had probably set all the pins 20 minutes prior and just didn't know it yet cuz my tension tool was binding slightly. Give it a good push now and then and you may be surprised
The 5100 and the 5200 that I own have serrated spool pins and serrated key pins, so expect some funny business. I repinned one with spools in all 5 positions and had a really tough time, but you will eventually get it if you do not give up. Just don't drill it till you can pick it! Then when you can pick it, don't drill it!
I dunno if this rambling will help, but keep tapping at the pins and eventually you will be able to recognize the feel even if it is more unconsciously than consciously. I am half awake by the time I get the thing open anyway.

There are so many serrations that it is hard to feel the spools so just forget about them until the plug turns a bit without breaking loose. Then neutralize them!
Do a search for spools or mushrooms for e better explanation than I could give right now about how to deal with them, of course
These are my favorite locks right now because they are pretty darn hard to pick

They are a real challenge for me.