From left to right I have the St4-26 spring, the same spring cut to the length I tested, my original bolt spring, a 12649 spring, the 12649 spring cut to length, and my original hammer spring.
To start, I wanted to get the bolt into the same general specs as an M1A1 which would be 7-15 pounds of spring pressure at the start of pulling back the bolt, and full rearward travel. My 1927 with all three springs went from 5 to 32 pounds as issued. The pair of springs that move the bolt went from 5 - 22 pounds and the hammer spring went from 6-10 pounds on my gun (it's short enough that it doesn't really put any pressure on the bolt until it moves a fraction of an inch, then there is basically 6 pounds of force needed to move it).
What I wanted was a hammer spring as weak as possible (but would still explode a primer) and the paired springs which move the bolt as strong as possible. That I felt would remove as much as possible the friction between the striker and the bolt, and still drive a cartridge out of a magazine.
I bought several springs after talking with an engineer over the phone. It's not perfect, but perhaps some of you might want to experiment while we are waiting for Dave to get his stuff for sale.
I ordered four different of the weakest springs I could get. For the pair of springs at the bottom of the bolt, I ended up with springs that were just to weak, even with every bit of length I could cram in there. So, the solution, use one original 1927 spring, and one of the purchased ones.
For the hammer spring, I cut a purchased spring down to the minimum length where it would provide just a little pressure an the hammer, ended up about the same length as the original 1927 spring.
So, what I got was a bolt that started moving at 5 pounds, and reached 21 pounds at full rearward travel. The hammer spring part of that was 1 to 6 pounds, and the unmatched pair on the bottom of the bolt went from 4 to 15 pounds. While not quite as nice as the M1A1 for pulling back the bolt, it was much better than the original bolt extraction force.
I had time (between pheasant hunts) for a short test. 50 rounds of Wolf out of a drum. I ended up with the hammer spring just a touch on the weak side as three rounds did not fire. The primers were very lightly dented. Otherwise, the bolt fully seated the rounds and the gun worked as I would like. I did forget to oil things up really well before leaving the house, so all the bolt parts were pretty dry. That little bit might make the difference with wolf, and perhaps other ammo might be a little more primer sensative.
I may talk to the engineers at Century again and see if they could provide something just a little different. A guy could possibly cut the original 1927 springs down a little, but then you would be sacrificing some of the resistance to motion that the bolt needs to have. As tested the wolf cases were not expanded any more than original spring expansion.
If anybody wants to try this stuff themselves, I contacted Century Spring Corp 800-237-5225. The small diameter recoil spring I ordered was number ST4-26 and the larger hammer spring was number 12649. The two springs cost about $4-$8 each. I'd like to have added one of PK's recoil buffers to the back of the action, but I just couldn't find the extra one I had on hand when I went to shoot.
Dave, if you are out there reading this, we need you to get your springs on the market.
