when I first started researching this shotgun on the internet, I googled
"acier cockerill" and found this website
http://piterhunt.ru/Library/satinskiy/kleyma/index.htm
I had a Russian friend translate the pertinant portion. I've lost his e-mail, but the impression he gave me was that while cockerill steel was commonly used by many makers, like ChiefShotguns points out, only ML would use the rooster.