Originally Posted by desertT1
Very clever. I don't get how it keeps from firing. Just the tension the spring loaded bar pressing against the bolt head is enough?
Originally Posted by Grendal50
I see a little notch to hold the end of the bolt.
Yes, there is a notch in there, and two springs altogether. The spool is balanced (same front and back bores), so under pressure it doesn't want to move, especially with a little seal friction. It's a bit of a mouse trap. The [spool] spring lets you set it easily with a thumb push and pushes the spool open when the brass sear drops (which is hinged on the pin going through the stock). The [spool] spring pushes against the back of the breech plug and the big shoulder on the spool. The hump in the middle just helps keep the spring aligned (well, that's why I put it there). The bolt head is actually the sear engagement adjustment too. It lets me set the exact position for the forward seal on the spool, after the body is so carefully mounted.
I was originally going to make it un-balanced so that the spool naturally wanted to go backwards, but I didn't want my sear tension varying with my chamber pressure, which I wasn't sure what the pressure would be in the end.
The spool travel is about .2" I think. I started out to make everything 1/4" here and there with 3/8" bores, but then it all needed to fit together. The back bore is long enough that the rear seal won't clear.