Try it without taking it out first. You aren't going to hurt anything. If that doesn't work, it's simple to take out as well.

Take the plunger out before you degauss it! You run the risk of generating a current on the coil (even if it's unplugged BTW) when you turn on the degausser. Same theory as a Transformer. Also Tape down the plunger to a surface so it won't jump around.

No need to remove the plunger. Any current that is induced in the coil will dissipate through the diode.

Wrong! Your dealing with AC current Not DC! Travels both ways. Every half cycle, current is traveling the opposite direction that the diode would normally divert the collapse voltage to.
plus you are exposing other components on the play-feild to the degausser is near (remember a degaussing ring is about 15" in diameter).
And you probably won't degasses the plunger as well or at all with a coil wrapped around / adjacent to it.

Agreed I would absolutely take it out before doing this or you are going to likely have a huge project on your hands.

Another words. No, no one has tried this before. Lots of smart guys with good theories but no one knows for sure. So unless you like being the test subject id take that plunger out.

Why do you think it's magnetic vs mechanical in the first place? Have you taken apart and cleaned the solenoid mech? One of mine does the same thing intermittently and I haven't gotten to it yet.

Not just a theory. Place a coil with an A/C Current on it (the degausser) next to another wire winding (a pinball coil for example), the other winding produces an A / C current. Basic transformer operation. Put a meter on a coil, and hit it with a degausser and watch what happens on the meter while the degausser is on.

I'd have to agree with this. I have seen magnetized plungers and stops before, but they are rare.
It's much more likely to be a damaged plunger, damaged coil stop, or other worn / misaligned parts.

Mine does that ocassionally as well. I read somewhere that its the wire loom that causes this so, I replaced it, not fixed. I also replaced the coil sleeve and that did not help. I would be interested to see if you find the problem with yours.

Ok my guess would be that perhaps the angle that the plunger travels through the sleeve is slightly off causing occasional friction or that wires are getting into the linkage.

I started experiencing this exact problem with my right cannon plunger a while back. I just got done tearing into it and found that a groove had been pounded into the bracket (see red arrow) by the retaining cap on the end of the plunger. That cap, which has a relatively sharp edge, was getting stuck in the groove, which was frequently causing the plunger to stick when the cannon went through testing at start-up. I fixed the problem by removing that bracket and polishing down the groove with a steel wheel brush. It's working great now, no more stuck plunger!! Hope this tip helps somebody someday.

STtNG_Cannon.jpg

I had the same problem after rebuilding the gun launchers. Found the sleeve was to short. I replace it with a slightly longer one and it did not experience the same issue. Turns out when I put the guns back together I must have grabbed the wrong sleeve as one gun had longer one, other gun had shorter one. Both have longer sleeve and have not had any sticking issues. Also when I was moving it by hand while the shorter sleeve was in place I felt the slightest catch, that was the clue that lead me to notice the sleeve difference between the two guns. All good now!

Use a tape deck head degausser on the plunger.