So hammer forging makes a "stronger" barrel....in what ways?

[ABNAK]

Most agree they wear at least a little longer than a regular barrel from a chamber/bore point of view. But what about the flexural strength of a barrel made by hammer forging?

If you took two identical length/weight/profile barrels made from the same steel, one hammer forged, the other not, which would require more foot/pounds of force to BEND it? i.e. are hammer forged barrels stronger in that regard.

[vicious_cb]

Most agree they wear at least a little longer than a regular barrel from a chamber/bore point of view. But what about the flexural strength of a barrel made by hammer forging?

If you took two identical length/weight/profile barrels made from the same steel, one hammer forged, the other not, which would require more foot/pounds of force to BEND it? i.e. are hammer forged barrels stronger in that regard.
'
No,not bending force. CHF induces what is called autofrettage or an internal "negative stress" that points inward towards the center of the bore. This directly opposes the "positive stresses" from firing a round which wants to push outwards and burst the barrel. For example take 2 barrels of the same diameter, weight ect, one that has been autofretted via CHF and one that has not. Now fire an over pressured round through both of them, the CHF barrel can contain the pressure because it started out in a "negative stress" state while the non-CHF barrel will burst from the pressure because it started out in a "neutral state" ie no negative or inward pointing stress to begin with.

[Mjolnir]

Most agree they wear at least a little longer than a regular barrel from a chamber/bore point of view. But what about the flexural strength of a barrel made by hammer forging?

If you took two identical length/weight/profile barrels made from the same steel, one hammer forged, the other not, which would require more foot/pounds of force to BEND it? i.e. are hammer forged barrels stronger in that regard.

Yes, due to smaller, controlled grain structure. But the loading you described isn’t relevant how a rifle barrel is utilized.

Look at the bore. The lands and grooves will be stronger and harder and resist microcracking better than a cut rifled or button rifled barrels due to the refined grain structure from cold working the barrel blank.


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[Mjolnir]

'
No,not bending force. CHF induces what is called autofrettage or an internal "negative stress" that points inward towards the center of the bore. This directly opposes the "positive stresses" from firing a round which wants to push outwards and burst the barrel. For example take 2 barrels of the same diameter, weight ect, one that has been autofretted via CHF and one that has not. Now fire an over pressured round through both of them, the CHF barrel can contain the pressure because it started out in a "negative stress" state while the non-CHF barrel will burst from the pressure because it started out in a "neutral state" ie no negative or inward pointing stress to begin with.

I forgot about that.

[emoji1431]


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[ABNAK]

'
No,not bending force. CHF induces what is called autofrettage or an internal "negative stress" that points inward towards the center of the bore. This directly opposes the "positive stresses" from firing a round which wants to push outwards and burst the barrel. For example take 2 barrels of the same diameter, weight ect, one that has been autofretted via CHF and one that has not. Now fire an over pressured round through both of them, the CHF barrel can contain the pressure because it started out in a "negative stress" state while the non-CHF barrel will burst from the pressure because it started out in a "neutral state" ie no negative or inward pointing stress to begin with.

Okay, that's what I was driving at. Thanks!

[lysander]

'
No,not bending force. CHF induces what is called autofrettage or an internal "negative stress" that points inward towards the center of the bore. This directly opposes the "positive stresses" from firing a round which wants to push outwards and burst the barrel. For example take 2 barrels of the same diameter, weight ect, one that has been autofretted via CHF and one that has not. Now fire an over pressured round through both of them, the CHF barrel can contain the pressure because it started out in a "negative stress" state while the non-CHF barrel will burst from the pressure because it started out in a "neutral state" ie no negative or inward pointing stress to begin with.
Actually, no.

Autofrettage is when the interior surface of the bore is compressed from the inside to slightly past the yield point, usually by hydraulic pressure, while the exterior of the barrel is not allowed to reach the yield point. This puts the interior bore in compression and the exterior in tension. This has to be done after all machining on the barrel is finished. This is done on large artillery and tank barrels.

During rotary swaging or rotary hammer forging, the hole in the blank is larger than the mandrel and the cold working process collapses the interior onto the mandrel. This forming process does, as you say, put the interior in compression and the exterior in tension, but, after cold working, in all cases, the finished blank must be stress relieved to relieve these internal stresses inside the barrel. Otherwise, something as simple as cutting the threads in the muzzle or chamber would remove the material in tension (outer surface) and the internal surfaces, no longer constrained, would be allowed to expand, resulting in an increase in bore diameter. So, this whole advantage is lost due to the fact that there have to be post-forming machining done on the blank.

(By the way, button rifling does the same thing. By pulling the rifling button through the bore, the area around the grooves is put in compression, while the rest of the barrel must contain this stress and is in tension. Similarly, and I have seen it happen, if the blank is not properly stress relieved, the bore will grow about .0005 to .001" after something as simple as threading the muzzle.)

Besides the stresses in small arms barrels are relatively low and the wall thickness required for simple stiffness and heat absorption results in a safety factor 3 of 4, more than adequate and no need to worry about popping open under high pressure cartridges... (see below)

The only real advantages of rotary swaging or rotary forging for small arms is the more uniform and reduced grain size, more uniform bore dimension, straighter bores, and faster more economical production. For big guns that work with lower safety factors there are additional advantages: greater fatigue resistance, and increased resistance to bending.

http://i61.photobucket.com/albums/h53/jntmjt1/Screenshot%202016-09-07%20at%209.56.58%20PM_zpsswbwoz6n.png
http://i61.photobucket.com/albums/h53/jntmjt1/Screenshot%202016-09-07%20at%209.51.30%20PM_zpsuauolkjb.png

[odugrad]

Wow. I'm learning a lot here.