Sear spring vs tumbler engagement

[somehippy]

Last week I made myself a tumbler from a large old bolt, armed with a hacksaw, files and a drill press.  It turned out pretty good (I'd post pics but my phone is being wonky), got my notches in the right places, the stirrup arm is also the stop as to not allow over travel past the full cock notch and it's fairly square even. I was pretty happy with myself, but for the life of me I cannot get it to hold at full cock, my sear tip and notch seem good and square but it just keeps slipping, ive kept honing both faces to true it up best I can to no avail and don't want to make any unnecessary slop past the full cock notch after getting it nice and tight.  I got thinking though, perhaps my sear spring is too week to hold properly?  I did harden my tumbler but I may have went too far tempering, it'll file but not like it did "raw".

So where might my trouble be?  I'll try to post pics if I can get on a computer later.

Thanks

[Hungry Horse]

You should not need a sear spring to keep the sear in the tumbler notch. The spring is strictly a mechanism to insure that the nose of the sear arrives in the notch in the tumbler. Your notch in the tumbler should have a slight undercut.

  Hungry Horse

[rich pierce]

Must be the angle of the nose or the angle of the notch do not both point to the pivot point of the tumbler axle.

[somehippy]

The notch does a have a slight undercut, maybe I need to go in a but more. Rich, I've heard about the relation of the notch angle to the tumbler axel, I just have a tough time visualizing what is meant by this for some reason lol.  Could you elaborate a bit for a simple fella like me?  Thanks

[rich pierce]

Use the center of the tumbler axle as the center of your tumbler. Draw a line straight from there to establish the front working edge of the full cock notch. Cut or file the notch. Making sure the sear nose is completely free to engage the notch without any other part of the sear touching the tumbler, file the nose angle to match the same angle.

[somehippy]

I think I get it, thanks, hopefully get er working this afternoon. If I can file it should I reharden it?

[rich pierce]

If you can file it, needs hardening and tempering.

[westbj2]

In an ideal world, strike a line thru the center of the tumbler axle and across the face of the full cock notch.  Strike another line thru the center of the sear pivot, then extend this line so that it intersects the other line at exactly 90 degrees.  Your sear nose wants to correspond to these angles.  No sear spring needed except to force engagement.
Jim

[SingleMalt]

I'm not a metallurgist, but I'm pretty certain the type of steel is equally important.  A low carbon steel, won't harden enough to avoid wear like it's high carbon cousin.  Even with a carborisng agent.  I hope you used a grade 8 or 10 for stock.  That should harden fine.

[somehippy]

Success!  got my notch fixed and it hardened nicely (at least I had scraps from the bolt to test on). My rifle might finally shoot now! Hopefully get that done tomorrow and post some pics, thank you every one for the help.  One happy hippy here

[rich pierce]

Good going.  That's a real project!