Digital 3D Sako L579

[bloorooster]

The very lucky Kentucky dude messed up by using a specialized military armor piercing round not designed for use with a muzzle break (sabot) ..while trying to shoot a hole through a fire hydrant. A very unrealistic, real life scenario. It’s almost impossible to field dress a fire hydrant without a cutting torch and side grinder!

 

[stonecreek]

Very interesting work, Tillyman. I'm glad you point out several times that it is theoretical in regard to the bolt/action deformation since the brass case would be destroyed at much lower pressures and the escaping gas would create a much different set of circumstances. But your analysis does do a great job of illustrating what such theoretical pressures would do in an action.

I'm always surprised when people argue about the "strength" of various centerfire actions. The fact is that virtually any action made for a centerfire round is orders of magnitude stronger than the thin brass case which is the "bladder" that contains the pressure. The only reason that you don't load a .30-30 to the same pressures as a .300 WSM is that the typical action for a .30-30 like a Winchester 94 is stretchy, allowing excess deformation of the case which would result in a jammed action at such pressures. A Winchester 94 isn't going to "blow up" at 65,000 PSI, but other bad things will happen.

Some antique actions may be made with soft steel or improperly hardened steel which can eventually be damaged by excessive pressures, but no relatively "modern" centerfire action is going to allow the bolt to come flying out backwards regardless of how much pressure is generated by an overload -- or more commonly, a round mistakenly loaded with a much faster-burning powder than is normally used in a given round.

 

[Laddie1012]

It can but this was just a quick study so I used default settings for 4340 tool steel normalised not hardened to a specific Rockwell level.
I’m not sure exactly what steel or heat treatment Sako used for the L579 action back in the day... it was also supposedly drop-forged which would increase toughness.
So 4340 would be more malleable in the normalised state... without specific material and heat treatment details any FEA study can only be an approximation.

Interesting stuff! For ~ 0.4% carbon steels like 4140 and 1045 it's usual to assume the heat treatment like normalizing or "fully killed" has a slightly higher stress at the surface unless it is machined down below 5mm under the skin. Normalizing is usually just to keep the fabrication and machining easy so stressed components don't distort while machining. These .4% shaft steels machine like a dream and will flame harden very well but then they become fragile at stress raiser points.

P.S. the cute part of a 9.5 twist barrel in a 7mm is the projectile is spinning over 200,000 RPM. Extreme stuff...