On the 1928 Thompson, we see the round buffer, and pilot, with the bolt impacting on the metal pilot, roughly 15% of the surface area. It is as though the pilot was designed with only the 1921 spring in mind, not the bolt, not the receiver...? The pilot also is shorter, leaving a gap about 1/2 where the spring can naturally bind. This generates rather high/uneven loading and stress.
"There's no engineering justification for the 1928 design!!!!"
Yet on the M1, the transition to a buffer that matches the bolt face occurs, as well as a method to insert the buffer/spring base. Eliminating the fiddly 28 system.
The "PK" hybrid buffer eliminates the drawbacks of the 28 spring, and "complexity" of the buffer discs, however leaving the metal to metal impact between the rear bolt face/actuator and the pilot, and requires the fiddly installation not seen with the M1.
With nearly an inch of extra/wasted bolt stroke in the receiver, there is plenty of room to experiment with new designs that may increase the longevity of an inevitability fatigued receiver.
Reverting to a 2 piece system that eliminated metal to metal contact would be wise. There are new materials we could use in place of fiber disc stacks, such as a urethane insert of varying durometer, or even a small piece of 28 recoil spring to speed things up, a la speed bolt.
Reading the patents, it's clear the inventor was limited by present day technologies and often spoke of using composites or sythetics, although out of reach.
I propose simply a 21 pilot, with recess for an M1 style buffer that matches the rear face of the bolt. A bit like the "2M2" 2B etc. as well as an variety of inserts for the 21 buffer tubes (which possibly could be lengthened to reduce spring bind)
Simply in an interest to keep all the old Thompson running well into the future, possibly better. Blown out rear ends will become a thing with enough rounds downrange.
Discussion is welcome,
Edited by Scrambles, 17 January 2018 - 03:16 PM.