How likely is it that you would see a crack before a bolt breaks at the cam pin hole? I've seen a few break - but I don't recall ever seeing a crack in a bolt when inspecting rifles.

Experience, please?

All the ones that I have seen crack, never showed any signs of pre-cracking.  They just cracked all the way at once, with no warning.  

Mostly, the problem is the steel is hardened too much (defective bolt-surfaced harden too deep), which makes it brittle as hell.  Once the metal stress factures, it snaps the entire bolt, like splitting a dry log with an axe.

Most likely you won't see the tell tales w/o the use of magnification or an inspection kit. Helps to degrease the part thoroughly and I've heard that black light helps too. If you can lay hands on the penetrant kit Sam uses you're golden. Could always have them MagnaFLuxed yearly too.

You have any recommendations for companies that do this and what they charge approximately?  TIA.

You can do it your self.  

All you need to do is to magnetize the stripped bolt (power supply and some wire, or a strong magnet) then powder flux the bolts to see if there is signs of cracking (a crack in the metal will break the electrical/ magnetized polarity flow and you will see the crack by a build up of power at the crack).  Just keep in mind that any cracks on the bolt will be small, so you will need to magnify the cam location to see the start of any cracking.


To give you idea of MagnaFLuxing, A engine head that has been magufluxed to find a crack.
[img]http://www.merkurxr4ti.com/ref/magnaflux/mag1.jpg[/img]

Powder flux?

What kind of powder?  I am greatful for all the AWESOME info but could you explain it a little more for me?

“Magnetic particle inspection is based on the fact that a crack in a magnetized ferromagnetic part creates a small magnetic field on the surface of that part. When iron powder is sprayed onto the part, the field acts as a little magnet to attract the powder to the crack. You may not be able to see a crack, but you are able to see the iron powder collecting at the magnetic field in and around the crack. The iron powder used in wet horizontal units is contained in water or oil bath. In fluorescent inspection, the iron powder is encapsulated in a fluorescent pigment. When the part is sprayed with the solution, the iron dust settles in the cracks and brightly shines when viewed under a black light.”

[url]http://www.puertoricosuppliers.com/brand/prodcat_brand_1.cfm?Brand_ID=424&Cat_ID=162[/url]

so dano is that the crack on the intake valve port?

Yes, it's circled in yellow.