What if Bolt Locking lugs not bearing Fully/Symmetrically ?

[gunsandgunsmithing]

3.1416*r*r*psi = bolt thrust. A .308 case has about a .385 id diameter so, radius being half of diameter, 3.1416x.1925x.1925x65000psi=7567psi of bolt thrust

I believe this formula to be correct but someone please correct me if I'm wrong. I wouldn't expect brass to withstand that much rearward thrust for one firing, much less multiple load and fires. This formula does not account for brass gripping the chamber wall but I certainly would not want to stand behind that much thrust with only that thin piece of brass between me and that much pressure.

 

[Alex Wheeler]

The chamber wall does play a large part. My experiments with chamber finish have shown me that. But If you can turn brass plastic and make it flow into the ejector hole thats a lot of force. I do remember reading of an experiment with a straight wall case, low pressures, and a lever action. But high pressures are the norm these days.

 

[Laurie]

3.1416*r*r*psi = bolt thrust. A .308 case has about a .385 id diameter so, radius being half of diameter, 3.1416x.1925x.1925x65000psi=7567psi of bolt thrust

I believe this formula to be correct but someone please correct me if I'm wrong. I wouldn't expect brass to withstand that much rearward thrust for one firing, much less multiple load and fires. This formula does not account for brass gripping the chamber wall but I certainly would not want to stand behind that much thrust with only that thin piece of brass between me and that much pressure.

Until relatively recently, all British military firearms were proof-tested by firing using an over-pressure proof round whose case was in addition oiled to stop the walls gripping the chamber and maximise rearward case-head thrust on the bolt. The resulting proof pressure was shown in 'tons' not psi, 303 being ~16 tons and 7.62mm 18 IIRC.

Although not a practice I'd recommend, and proof testing for obvious reasons doesn't see anybody hold the test firearm, or even remain in the vicinity, hundreds of thousands (if not millions) of new and factory reconditioned rifles were proofed / re-proofed using this method with a virtually nil failure / breakage rate.

So, it seems that case-heads are rather stronger and take higher pressures than one might imagine.

 

[Dusty Stevens]

Until relatively recently, all British military firearms were proof-tested by firing using an over-pressure proof round whose case was in addition oiled to stop the walls gripping the chamber and maximise rearward case-head thrust on the bolt. The resulting proof pressure was shown in 'tons' not psi, 303 being ~16 tons and 7.62mm 18 IIRC.

Although not a practice I'd recommend, and proof testing for obvious reasons doesn't see anybody hold the test firearm, or even remain in the vicinity, hundreds of thousands (if not millions) of new and factory reconditioned rifles were proofed / re-proofed using this method with a virtually nil failure / breakage rate.

So, it seems that case-heads are rather stronger and take higher pressures than one might imagine.

And farley recalled a run of actions due to bolt lugs shearing off of one so there is quite a lot of pressure involved. That is why every single remington action ever made has a hardness test done on a lug. Thats what the little dimple is

 

[STS]

I'm pretty sure that little dimple is a headspace indicator so they could match up bolts to barrels so that headspace is correct. Seems like Butch Lambert forwarded that info from Remington if I remember correctly.

 

[Dusty Stevens]

I'm pretty sure that little dimple is a headspace indicator so they could match up bolts to barrels so that headspace is correct. Seems like Butch Lambert forwarded that info from Remington if I remember correctly.

I thought thats what the serial number on the bolt did?

 

[STS]