Dimples on receiver and bolt

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Originally Posted by Bill Ricca

On the fun side look at the M14 Picture and see the military description of the punch mark. That word cannot be used on many forums "Prick Punch Markings". I could not post it on some forums due to the nasty word.

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That is silly as it's name is "Prick Punch". Any machinist knows and has them. I guess you can't call a donkey an "***" either. Got edited out.

Holy moly, what are we becoming.

Jim

Many Thanks Bill ! Your input as usual, is very much appreciated. Mike.

This may sound like a dumb question, but what's the difference between "High Pressure Testing" and Hardness testing. Doesn't the "high pressure test" conclude that the steel is hard enough to withstand the "high pressure prick"? Or I guess I should say "Prick Punch".

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Originally Posted by INLAND44

I mean, how do you hit a punch with a certain diameter, hardness and tip shape with a hammer, to deliver an exact and repeatable force?

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With a specialist machine, as you guessed. A local gunsmith, who is also a qualified toolmaker, even has one!

Here are some examples:
http://www.hardnesstesters.com/Products/index.aspx

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Originally Posted by ABPOS

This may sound like a dumb question, but what's the difference between "High Pressure Testing" and Hardness testing.

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High pressure testing applies a force over a considerable area, but remains within the elastic limits of the material. A proof round, for instance, is not supposed to permanently distort the chamber! But the old CUP measurement was derived from the measured distortion of the copper block. The intention is to check that the material under test will indeed not be stressed beyond the elastic limit in the intended appplication.

Hardness testing measures just what that elastic limit is, by applying a much higher force than a pressure test, but to a very small area that is indeed distorted beyond the elastic limit, and the hardness figure is derived from measurement of that distortion. If the pressure produced on the tiny spot of a Rockwell tester were to be applied all over a chamber, the chamber would not just distort, it would explode.

After the high pressure round is fired, the bolt, barrel and/or chamber are checked for cracks and other damages. The round bolts from the 1960's that had the M marking were often advertised as Winchester (upsidedown M). The M meant the bolt was Magnetic Particle Tested or Magafluzed and no cracks were found. The punches and/or the P means the items were tested and passed.

I have the pressure of the different Test Rounds and the pressure is not the only difference. The types of powder change the pressure flow so the pressure is different from standard ammunition as the bullet travels though the rifling. I do not remember each one.

That high pressure test will show that normal ammunition will not hurt the tested item.

Hardness testing is usually part of production and will see that the item will not bent, break, or have other problems.

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Originally Posted by Bill Ricca

There are some barrels that have the P and the punch mark inside the P. I guess those were spare barrels that were tested and P marked. Then assembled in a rifle tested and the punch added to the P. Just a guess.

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I think the punch mark on a carbine barrel was NPM's own proof mark, any "P" would have been applied by the barrel's maker after proof firing (NPM didn't make their own barrels).

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Originally Posted by Patrick Chadwick

High pressure testing applies a force over a considerable area, but remains within the elastic limits of the material. A proof round, for instance, is not supposed to permanently distort the chamber! But the old CUP measurement was derived from the measured distortion of the copper block. The intention is to check that the material under test will indeed not be stressed beyond the elastic limit in the intended appplication.

Hardness testing measures just what that elastic limit is, by applying a much higher force than a pressure test, but to a very small area that is indeed distorted beyond the elastic limit, and the hardness figure is derived from measurement of that distortion. If the pressure produced on the tiny spot of a Rockwell tester were to be applied all over a chamber, the chamber would not just distort, it would explode.

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That makes sense. But for some reason, I'm getting the idea that the "high pressure test" is an actual round being fired out of the chamber. But that doesn't seem to make sense with the dimples or "pricking". I'm probably just reading it wrong and am confused. I can't really see bills pictures all that well, other than it looks like the rifle in some kind of contraption. It does look like it might be allowing something to come out the muzzle, clear of the device though. But why would that leave a dimple on the oustide of the bolt and receiver? But again, I'm probably just not understanding it correctly. Because there seem to be more evidence of something actually striking those areas. Right?

---------- Post added at 12:11 PM ---------- Previous post was at 12:10 PM ----------

Or maybe it's both?

After the rifle has been test fired with the high pressure round and has passed inspection, they place the punch marks on the bolt and receiver to indicate such.
- Bob

OK, got it. Are bolts marked anywhere else with any letters typically?