So lay a blonde hair on a paper matchbook cover and you are looking at about .020" That's not a lot of material between 8000-12000 psi of hot powder gasses and your fingers and eyes.
"IF" you have .020" wall over the "Chamber" which is where that 8-12Kpsi occurs you are "In a Heap of Trouble Boy.
W W Greener reported on making a bbl so thin, "In the forward Section" that after it had "Held" for a number of shots with normal shells, he ripped it open with his pen knife. As long as no obstruction is present there is little danger of "Blowing" the forward half of a bbl.
Incidently. though I have not personally done a lot of checking I was always told a "True" Blonde's hair would mic too about .003", A Brunette's .0035" & a Red Head's @ 004".
Though not quite as much fun an easier solution is to simply lay a strip of 20# printer paper on the matchbook cover.
