I've flown with checked firearms on DL without issue for several years, up until a couple of months ago.
In this case, departing ATL was no issue, I had a couple of pistols, a suppressor and a couple hundred rounds in a Pelican case with 2 pad locks, DL agent visually verified contents and then tagged with the extra "CAGPT - Check and give protection to" tag, then TSA did a visual inspection and swab, put the case in my checked bag and locked that bag.
Upon arriving at destination, it was sent to the baggage service office, black zip tie added around the bag and I retrieved it ... so far, so good, but my return flight didn't go so well.
Checked in for my flt back to ATL, similar DL and TSA checks, CAGPT tag attached, but this time TSA didn't want to look inside, and the bag was loaded. I get to ATL and head over to the oversized belt where they have an area for retrieving firearms, after standing there for about 40 mins the reps said they didn't have my bag. I start to head over to the baggage service office and as I'm passing the carousel for my flight, low and behold, there is my bag riding in circles with other regular bags.
As I was retrieving my bag, a red coat happened to be passing by and I asked if policies had recently changed, she saw the CAGPT tag and said no and immediately began making radio and phone calls. They added a zip tie to it and as I left, a few other DL staff had joined her and they were discussing the mishandling.
As noted by another member above, one of my pet peeves of traveling with firearms is the CAGPT "neon sign" label just screaming steal me! TSA regs state that the airline is not to label a bag to indicate a firearm is within, but I feel the CAGPT label does just that (although they are able to do so as it does not directly state that it's a firearm, and could be other high VAL).
Anyway, I'm a bit leery now, especially with a suppressor on a tax stamp.