@sestoppelman we flew to joburg on 26 June and got back on 8 July. We flew on delta from Phoenix to Atlanta to joburg.
I went through all the hassle to get an EIN number for my temporary export. This all proved to be a hassle as it never came up.
While getting my 4457 at my local CBP office, I asked about it and the agent said that it's not necessary right now. She was not sure when, if ever, the EIN would actually be needed.
Coming back in to Atlanta, we went through the global entry kiosk, expediting the whole immigration process. I then went to the oversized baggage area and waited for my rifle. CBP will not start checking rifle cases until all cases from the flight have arrived. From getting to the oversized baggage room to walking out with my rifle took about 30 minutes, mostly due to waiting for all the bags to arrive.
The CBP agent checked my rifle against my 4457, confirming serial number. That was it.
Of note, I brought along a supressor. No issues in either south Africa or Atlanta. I noted it on my 4457 before departing. Coming back in, the agents didn't even look at it. They were just concerned with the rifle serial number.
All told, the whole process was way less painful than I expected. The most frustrating part was taking that online quiz while trying to get my EIN, which was a waste of time.