Sam, about a year ago I read an article, I believe in a magazine called
Military Antiques, which dealt with the issue of the Blish device. It was controversial from the start. A big question was what, if anything it did.
It was John Thompson's contention that it worked by a phenomenon callled differential of friction. The device, being made of a different metal than the rest, delayed the recoil through friction.
The authors of the article obtained a 1928 Thompson and an extra Blish Lock. They first established the actual firing rate of the Thompson they were using, then milled off the ears of the extra Blish (the trapezoidal projections present in the above photograph is what I am refering too, for those who don't know how Thompson's work). When they assembled this altered lock into the weapon, they determined that the rate of fire had increased by about 200 RPM.
The device actually does work. What I forget is how they established
HOW it works. It doesn't work the way Mr. Thompson claimed; it works through a principle of leverage, since the Blishlock slides up and down inside the bolt at a different angle than the cuts inside the receiver are angled at.
The conclusion however is really unchanged; the Blish was eliminated in the M1 and M1A1 versions and simpler methods were employed to keep the rate of fire down to what the army desired, or closely enough to satisfy the army atleast. Despite the fact it actually did work albeit differently than originally believed, it was too complex and expensive for wartime production.
Despite that fact, I stubbornly insist I like the 1928 Thompsons better than the later versions. Just got rocks in my head 'bout it, I guess.
