New DI design I have been thinking about

[Sam Cade]

they determined that the rate of fire had increased by about 200 RPM.
*snip*

It was the just the weight removed. The was Blish literally dead weight...and it was a good thing.

From an old AR article:

Indeed, the Small Arms staff at Enfield predicted the alteration of the design of later Thompsons by removing the Blish lock completely and then firing the gun remotely under safe conditions. The results were instructive: “The rounds were fired, both ejection and extraction being satisfactory. The gun functioned well and the condition of the spent cases was found to be identical with that of the spent cases … fired with the wedge assembled to the gun.”

I wonder how they modified them, exactly, since IRRC you can't just pull the lock out and have a functional firearm.

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 at least.

The bolt weight was increased by a couple ounces.

 

[Tommygunn]

I believe a beefier recoil spring was introduced as well.
Here is, I think, the 1928 Thompson bolt disassembled.