Cases and Enfields and lube - Oh my!

[Edward Horton]

If you take the time to do some simple math with the figures below in blue you will see that there is approximately a 40% increase in bolt thrust with an oiled or greased cartridge. (Forgive me I rounded up, the actual figure from U.S.Military is 39.21568 % increase in pressure or bolt thrust.)

I keep furnishing data for you all to look at and you keep ignoring what I post and then complain I’m just parroting a bunch of garbage or what I’m posting isn’t useful. This information was first published in 1921 by the U.S. Military BUT the people who advocate greasing their cartridge cases seem to want to overlook this piece of vital information.

Then I ask myself why other people can’t figure out that an oiled or greased case adds 40% to you pressure or bolt thrust figures with all the data and information I have provided. The only difference between the 30-06 and .303 British is the .303 British is .010 smaller in base diameter and the pressure-bolt thrust figures would be very slightly less. (it might even drop to 39.2XXXX)

The real question here is do we believe the testing done at Springfield Armory and Frankford Arsenal or do we believe the people who say its safe to grease your cases.

And don’t tell me what Dick Culver wrote here is garbage or doesn’t apply to this subject.

When the "Tin Can" Changed History
By Dick Culver


While the 1920 NM Ammunition was accurate, it was still using a standard cupro-nickel jacketed bullet, although of the same 170 flat-based design as the 1921 projectile. The shooters of course, were solving the fouling problem with liberal applications of grease. Experiments at Springfield and Frankford disclosed that the 1920 NM Ammunition fired in a dry chamber gave approximately 51,000 psi, well within normal specifications. By carefully lubricating the bullet and case neck, the pressures rose to 59,000 psi. When the entire case was lubricated along with the chamber which was common (if unintended) when the cartridges were used in rapid-fire strings, the chamber pressure rose to a dangerous 71,000+ psi, the pressure normally attributed to a proof test load.

Physics and the Rifle Shooter

The inadvertently lubricated cartridge case was the worst problem as its sides were tapered. Normal ammunition forms a gas seal in the chamber due to a process known as obturation. Obturation is simply the expansion of the brass case, tightly sealing the chamber when the round is fired. This case expansion forces little fingers of brass to occupy unseen microscopic irregularities in the chamber walls. This is truly a good thing as it seals the chamber until the gas pressure has subsided. Unsealed chambers allow gas to blow back into the receiver, possibly injuring the shooter. The greasy cartridge case in a tapered chamber had two disastrous consequences. First, grease is incompressible and will not allow the case to expand
within the chamber as it was meant to do. Since the grease decreases the coefficient of friction and allows the cartridge case to slide in and out of the chamber more easily it precipitates what I call "the watermelon seed effect". This equates to the squeezing a fresh, wet watermelon seed between your fingers and having it squirt out into the grass. The greased, (and tapered) chamber has much the same effect on a brass cartridge case. Since the lack of compressibility of the grease prevents the case from expanding against the chamber walls and thus sealing the gas with normal obturation, the tapered case "squirts" to the rear with virtually all of the force of the combustion gasses being directed straight rearward against the bolt.