pressure signs

[bigedp51]

Even the military tells you to not lube your ammo, military chambers are larger in diameter and LONGER in headspace than standard SAAMI chambers.

Just one of the reasons that military headspace is longer is because the brass cartridge case is expendable. The longer headspaced military chamber reduces the dwell time the rear of the case is in contact with the bolt face and the force applied to the bolt face.

A lubed case increases bolt thrust, a dry case reduces bolt thrust due to the lower dwell time the rear of the case is in contact with the bolt face.

In simple English the dry cartridge case is acting like a shock absorber and reducing the force applied to the bolt face and and the dwell time the case in in contact with the bolt face.

Rifle Chamber Finish & Friction Effects
on Bolt Load and Case Head Thinning.
FEA Calculations done with LS-DYNA

http://www.varmintal.com/a243z.htm

The British used the base crusher system described below, and in order to measure total chamber pressure the cartridge had to be oiled to apply 100% of the chamber pressure to the copper crusher.

In Britain, a third set of crusher standards were developed, using a "base" crusher. The crusher was a short, thick tube placed behind a piston at the base of the cartridge, and the firing pin passed through the center. The cartridge case was well oiled before firing, to minimize cling to the chamber walls (if not oiled, the indicated pressures were about 40% lower). The units were generally stated in British long tons per square inch, or tsi. Pressures indicated by this method run 10 to 20% below those indicated by radial crushers. Kynamco in England still rates their production cartridges with this method.


From the British "Textbook of Small Arms" dated 1929

 

[mikecr]

IMO both sides in discussion are right -provided neither are taken to extremes.
Varmint Al covers it pretty well here: http://www.varmintal.net/a243z.htm

 

[bigedp51]

mikecr, look at my post above yours and the link I provided.
(we have two varmints running loose in the forum)

IMO both sides in discussion are right -provided neither are taken to extremes.
Varmint Al covers it pretty well here: http://www.varmintal.net/a243z.htm

You are correct, and there are intelligent people shooting in this forum who understand the word "bolt thrust" and how strong their "MODERN BOLT ACTION" rifles are. The problem is "just lube your cases" has spread far and wide and is getting out of hand.

The problem with lubing your case is its like being in the boxing ring, dropping your guard and leaning forward into a right hook and hoping for the best. And my point being there are other ways to get the job done without taking it on the chin every time you pull the trigger.

What many people forget is that P.O. Ackley with his improved cartridges reduced bolt thrust while increasing chamber pressure.

"Handbook for Shooters and Reloaders" Vol. 1 1962 P.O.Ackley
Chapter 7 "Pressure" page 140
"To further illustrate this principal, and old, discarded, beat up Winchester Model 94 rifle was resurrected from the junk pile. The barrel was rechambered for the "improved" 30-30 with a 40 [degrees] shoulder and minimum body taper... [Ackley went on to get case separation with factory 30-30 ammo in a an oiled improved chamber with the barrel unscrewed 2 turns, but with a dry chamber the case formed but did not separate]"
Chapter 7 "Pressure" page 147
"To further prove the point, the locking lug was removed from the action entirely leaving the breech block or bolt with no means of support other than the finger lever. See illustrations. The rifle was fired several times with the barrel tight. All cases appeared to be normal except for excessive primer protrusion. Now to state that this action will handle only certain pressers, or that the brass case will not support any amount of pressure seems to be out of order. There is plenty of room for further testing along these lines but the tests described seem to indicate that a very small percentage of the CHAMBER pressure was transferred to the breech bolt in the form of thrust. In this test the barrel absorbed the pressure while the action merely furnish the means for detonating the cartridge except when the chamber was oily."


And again, NATO requirements for proofing military small arms requires two proof cartridges, one dry cartridge to proof the barrel and one oiled proof cartridge to proof the bolt and reciever and simulate the worst possible combat conditions.