The Thompson's mechanism of operation was based on a speculation called the Blisch effect. Named after A naval Commander, the theory was that two dissimilar metals will adhere to each other under extreme pressures. Thompson used this theory and listed it as the method of operation in his patents. In reality though the Blisch effect doesn't exist as would later be proven and observed. the design still proved successful and reliable despite this, and while it was designed as " Blisch lock" design. It turns out it was just another straight blow back design firing from an open blt. The Blisch effect has no bearing on it's operation in reality. The idea was this Blisch effect would temporarily lock the bolt closed against the barrel until chamber pressure dropped for the effect to cease. Luckily for Thomson the design worked on the proven blowback operation principles and the only thing holding the bolt closed while being fried is rthe heavy recoil spring.