Can a shooter tell the difference between shooting a blank and a regular lead round?

Yes, a blank has very little recoil compared to a normal rifle round. Yes, that is a myth.

I would say for most guns, shooting at the range, yeah, you'd probably feel the difference if you were accustomed to shooting live rounds from a particular gun, maybe even for guns with very little recoil.

A blank definitely has far less recoil than a round with a bullet.

I saw a YouTube video where someone picked up a M-134 Minigun and fired it with blank rounds. If you were to pick up and fire that same gun without blank rounds, you would go flying backwards and be knocked down (that gun must be mounted for it to be controllable).

It sounds like you want answers oriented around a firing squad. I think a person with a conscience that is appointed to participate in a legal firing squad can feel relieved that his pull of the trigger was inert. Maybe all of the squad fired blanks and the death bullet came from a remote appointee that has no problem knowing his bullet was the death blow. It is a fact that those kind do exist. Their conscience is so calloused over that it is just another duty to perform. If the event were captured on camera with the muzzle blasts from all the guns it would be a tell-tale

which of the guns fired a bullet and which did not.

I believe a moving bullet leaves a void in the wake that would show up on certain cameras or some eagle eyed person would notice where as a blank blast has a distinct shape. 

I do think the trigger person can tell if his shot was blank or not.

yes, they sound different and recoil different. live vs blank i mean. 

let me break this down, so you understand a bit more

theres three noise sources with firing a gun

the action

the sonic boom

the expanding gasses

two of those three are absent with blanks most of the time. action and sonic boom.

a blank CAN kill someone by expanding gasses alone if at the right distance to the muzzle, assuming it isnt a blank pistol.

The firing squad story is no myth. It was and still is being used in many countries' military and civilian law. In the US, the most recent execution by firing squad was a civilian case in Utah that occurred in 2010 and it was done just this way.  However, it is not just 1 member of the firing squad being issued a blank but could be 2 or more. I also remember reading a case how only one person in the squad was issued a real cartridge. This is one of the reason why the officer-in-charge's duty is to carry out the coup de grâce if the firing squad did not kill the condemned. 

As for felt recoil, the military and law-enforcemnt also has made it such that the felt recoil is less distinguishable between a real and blank cartridge. They do it by using a wax bullet and also difference in the charge/propellant which makes the difference in recoil less pronounced and so the members of the firing squad would not notice unless they have some experience and deliberately concentrate their attention to the recoil in which case they may notice the difference. But then why would anyone want to know they were the one who made the kill?

Yes you can tell a difference but if you remember a wad from a blank killed 

the Asian actor in The Crow. His name slips my memory at this moment 

but I know it.

Yes you can tell the difference in recoil.

Yes someone should be able to easily tell if they fired a blank rather than a regular .30-06 cartridge.  However, I can imagine in a real firing squad situation with a lot of nervousness and adrenaline that someone who fired a regular cartridge could convince themselves they only fired a blank to keep their conscious clear.

I believe this either a myth.   A blank looks visually different than a regular cartridge, so they could not fool anyone simply by issuing different ammo.  They would have to preload the execution rifles and randomly hand them to the shooters, which is also firearm handling no-no.

Keep tabs on South Carolina bill voted on to add firing squad execution choice to death row inmates and just maybe someone with REAL experience can answer your question(in a few years).

https://sports.yahoo.com/news/south-carolina-bill-...

Yes, a shooter can tell blanks from regular rounds. The most compatible firearm to shoot them is a revolver.

I have shot many blanks from a M1 Garand when in USMC training. The M1 is semi-auto and a blank adapter must be installed at the muzzle close to the gas port for the weapon to cycle. There is no felt recoil.  

Also own a Swiss Mauser that had a blank adapter attached to it when purchased but for a different purpose because the bolt action would easily cycle without an adapter. Blanks are very dangerous at close range unless the gases are diverted or reduced from the muzzle. 

Yes, a blank has far less felt recoil that an actual live round.