The rust marks on the liner seem to match up to the rust in the steel... ? The entrance hole seems larger than a rifle bullet... Once again, thats just how it looks to me? There is a good amount of space between the dome of the liner  and the inside dome area of the steel....

I could be completely wrong and I might be over thinking this but in my opinion the story is probably bogus as this was probably an old beat up surplus shell that someone shot then added a liner in order to increase the value of what many people would otherwise consider to be a candidate for a restoration project with little value (which kind of depends on whenever this might've been done). Another possibility is that they put the liner in it before shooting it but they shot it while it was sitting on something so the fixed loops lifted the shell up slightly separating the liner and the shell so the liner wasn't actually pressed against the shell separating it just enough for the bullet to slide against the liner without deforming/cracking it. But what are the odds that while someone is presumably wearing it a bullet penetrates the shell then somehow has enough room to slide against the liner and exit out the rear decimating the area yet barely damaging the liner and only in one small area. I would expect deformation or cracks/a hole (maybe not cracks but even some loose threads) around the impact zone on the liner. The addition of a repro headband and neckband is also a red flag in my opinion as the fact that the seller neglected to mention that they are repros indicates to me that they weren't the first to own it since they were added and probably don't know much about helmets so they were probably told a fairy tale by the previous owner or that they do know that they are repros and they added them to increase the value.   I just don't think that a bullet would've had enough room to penetrate the shell without causing more damage to the liner if it was on someone's head. And obviously anyone can buy an old beat up shell that some wouldn't see much value in and shoot it and sand the liner to increase their value.   Alternatively the shell could've already been shot when someone got it and then they got a somewhat cheap liner (for liners from WW2 anyways) from 1944-45 and sanded it to match the damage.

Thank you, it put an end to a dry month of wing hunting. 

Sad news...read of his passing when posted on FB. Prayers and blessing to friend and family

Not wanting to reinvent the wheel, what sources did you check? I’ll check the others in my library.

The following information is from TM 3-300 Ground Chemical Munitions 14 August 1956  

These pages are from the Army Ammunition Data Sheets on Military Pyrotechnics    

Thank you, I saw that today while searching.

Just came upon this thread... Here is a card from a nice grouping I acquired, that matches this threads theme.

What's the meaning of 'Whale'? It's the bombs or the phenomenon caused by the explosion.