I just found a very old thread on another site and learned
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The rear end of the bolt turns like a dial. Al says it is a bolt/hammer spring tensioner, which allows for the use of short cartridges. I.e., adjusting the spring tension allows .22 shorts to cycle the action. sounds cool, but I havent looked into it yet. how it is supposed to work, I haven't a clue.
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Later it goes on to say you can experiment with this knob for what ever round you have to get it to cycle properly. So it is in effect an adjustable gas block, sort of.