Reasons a live fire on a warbird can't be done

[p51]

The FAA isn't keen on ejecting brass from a .50, as I have heard.
Also, when transporting Class III weapons over any state lines, you have to fill out a form with the ATF ahead of time. I think that what stops most folks as you have to stay in a very tight area. Then, there's the range concerns as most privately-owned places aren't big enough to allow it.
I bet, generally, the lawyers are the biggest reason you don't see this much with live ammo.

[Cherrybomber13]

As much as I would love to see a live gun run at an event, I have to agree with Wilson up above, the left wingers would feed on it like flies on elephant poop and destroy the hobby.

[p51]

As much as I would love to see a live gun run at an event, I have to agree with Wilson up above, the left wingers would feed on it like flies on elephant poop and destroy the hobby.

Yep.
Imagine the press; "Privately-owned warplane strafes targets on the ground".
I once took part in a closed-to-the-public WW2 re-enactor event on a private range. We attacked some pre-made (unoccupied) bunkers with all manner of small arms. One guy even had a registered M1 bazooka and tried to have working rockets made, but too late for the event.
The local press found out and made a stink about it, saying there were civilians doing 'para-military training' right at the time the whole militia movement started making waves in the press.
The owner of the land got so much flak about it, he never allowed another such event.
That was in the 90s, imagine such a furor today, especially with an airplane which admittedly could far easier overshoot the range than people on the ground might.

[ZRX61]

When they made the 1989 movie "Memphis Belle", all the B-17s were armed with real M2, that fired blanks. Probably the first last and only time since WW2, that a group of B-17s were fully armed. One of them had a fully operable norden bombsight and associated gear to make a real bomb run.

No they weren't, I flew as a waist gunner during the filming & most of the guns were replicas that looked like junk from 30ft away.
One (or two) of them had blank firing guns in some of the positions.

[Tim Savage]

there was a AT-11 at OSH with twin gas guns, don't remember a T-6 with live guns

Bill Crones SNJ-5C. He fired blanks until a couple of WoA directors got a burr in their saddle and stopped it. Around 96 or 97