tl;dr: Yes, they can pick it up, no, you're not going to wind up locked in a subterranean hole.
I flew to a competition and had a return flight the same day. My carry-on bag also occasionally does duty as a range bag. Competition ran long, didn't have time to shower, and I typically opt out of the wave scanner. Had a bunch of weird-looking stuff in the bag (a cooler with cheese, which due to its density looks remarkably similar to explosives on the scanner), so they pulled it for secondary. Both my clothes and my bag popped.
(Yes, they do test their hands when they pat you down. That's what they're doing when they leave you to stand there and go over to the machine.)
I kept my hands where everyone could see them and calmly said, "I will probably test positive, I am a competitive shooter and I just finished a match." The TSA kid's face immediately relaxed a lot, though all of them were professional the whole way through.
I have also had my suitcase/gun case test positive when putting my locked firearm case through the baggage scanner. This was actually at O'Hare. They were cool, just had to wait for a supervisor.
So it might take you a few extra minutes, but I didn't miss either flight, and I was cutting it pretty close for one. If you wash your clothes, wipe down your cases, and/or change, it probably won't happen for you at all.
Glad you've had easy experiences. I can only imagine what could happen when you get that special snowflake tsa guy who snaps at the mention of the word "shooter", regardless of context.