what does lightly lubricating cases to conform to the chamber do that non lubricated cases do not do (firing a light load)?
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what does lightly lubricating cases to conform to the chamber do that non lubricated cases do not do (firing a light load)?
Two things.
1 it gives a very slight cushion between the case and the bore.
2nd it makes for easier removal of said case.
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And they may not form correctly.....if I understand the question correctly. I make sure my cases are wiped down before I fire form them. I haven't had any problems with extraction, but my fire form loads are generally fairly light loads. I do like to see holes on my targets, so I don't shoot cornmeal or wadded up cotton or anything like that, just mild loads. I have two Ackley Improved rifles that I load for.
Last edited by Tom W.; 09-13-2019 at 09:59 PM.
Tom
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Did I ever mention that I hate to trim brass?
When the firing pin digs into the primer the case is driven forwards in the chamber.
On a normal load the front part of the case will expand and grip the chamber and the rear part will stretch the brass to fill the space in front of the bolt.
Lube let the case slide back towards the bolt and the shoulder to form for maximum chamber fit.
Lube used on standard loads will increase bolt pressure to dangerous levels and are a big nono!
When I was fire forming some 8x56mm cases for my Swede roller that was chambered for 8x58mmRD I would, (1) Load light load of 8 grain of Unique, (2) lightly oil back half of case so the rim and base are against breach block so the base and the back half of the case is fully formed to the chamber shape. You want to be sure the load is light if fire forming with a lubricated case.
You might want to review the finite element analysis at Varmit Al's site. http://www.varmintal.com/amod7.htm
1. Many of us use brass that has been mechanically formed to fit the chamber with a little friction when the bolt is closed so those cases are not really driven forward.
2. Want to explain exactly how a thin film of oil raises pressure to a dangerous level?
I can understand a large quantity of grease blocking the bore causing problems but a little oil on the case is not a problem. Most guys that shoot rifles do not clean the oil out of the chamber and they never have a problem. In fact entire armies do just that.
Originally Posted by 17nut
EDG
Believe the issue of oil on the cases with full power loads is the case will not seize to the chamber walls and increase thrust on the bolt face. When forming cases with light loads oil will let the base of the case move into full contact with the bolt and the shoulder area will move forward. If forming rimmed or belted cases oiling is not needed as headspace is controlled by the rim or belt. Have only fire formed 30/40AI so don't know how true this theory of oiling cases is in reality.
Given that the pressure is the same in all directions, oiling the case can not increase “thrust” on the bolt face. Pressure in a closed vessel is the same in all directions. To claim otherwise is to violate a well understood principle of physics.
Pressure of full power loads is sufficient to move or stretch case to touch bolt whether oil is present or not.
A number of military arms deliberately oiled the case prior to firing.
Lube on the case will not and cannot increase pressure on the bolt to dangerous levels. If the pressure developed by the load is already safe for the rifle in question, oil will not change that.
Lubing the case is the only way to push the shoulder back forward when it's been moved too far back by improper sizing or use with light loads.
It is the explosion of the primer that drives the case forward, not the impact of the firing pin. Only a problem with bottleneck cases headspacing on the shoulder. Fix is to drill out the flash hole bigger, and use less energetic pistol primers.
Both things I learned of necessity when shooting plinking loads in my Dad's .35 Remington-chambered Marlin. My first cast-bullet rifle. Forty-odd years ago....egad how time flies! And how ignorant I was then, despite being almost 40 myself!
There's a lot of top authorities who say that lubed cases risk increasing bolt thrust. I'm not prepared to say more than that. Hatcher said it; I believe it.
Yes, there were a couple of machine gun designs that oiled the chamber. I've always assumed to solve an extraction problem inherent in weak design. The Italian Breda is the only name I can remember. It was a terrible solution - the chambers got fouled with dust very quickly, and extraction became far worse. British soldiers said to have gathered up dozens of jammed Bredas in Africa.
Cognitive Dissident
That is my understanding as well that lubed cases that have not been cleaned off would increase bolt thrust.
A hot number like a 22-250 cartridge with lots of body taper would compound that problem.
Add an action like a Remington 788 with rear locking lugs with all the above issues and now the bolt is getting swaged ever so shorter each shot.
In my case I have one of those but my brass stays dry because mostly I use the Lee Collet sizer die and you run your cases without lube on those.
Best regards
Three44s
Last edited by Three44s; 09-21-2019 at 08:57 PM.
Quote Originally Posted by Bret4207
“There is more to this than dumping lead in a hole.”
Hatcher confused their buildup of grease which is incompressible in the neck area of the bullet with something else. The grease he claimed increased “bolt thrust” (competitors were smearing on the cases at Camp Perry) actually left no room for the case to expand and release the bullet. This caused the problems he claimed to see, not “bolt thrust.”
The idea of lubricant increasing bolt thrust has been thoroughly discredited. By the same reasoning the idea of an improved case shape with less case taper such as an Ackley Improved reducing bolt thrust is also discredited. Whether a case be tapered or straight, once pressure reaches a level that exceeds the yield strength of the brass, the brass will stretch and allow the case head to touch the bolt. A straighter case wall will not help in that regard.
In other words, the two ideas are effectively refuted using the same valid reasoning. Also remember pressure cannot be multiplied in one direction and not others. As long as the pressure developed is within the rifle’s limits the case can be in a frictionless state as it lies in the chamber and the rifle will be fine because the pressure is fine, and pressure is the only outward force on the chamber and bolt that is present.
Pressure is the only thing acting on the case interior, and due to physical laws it is impossible to multiply pressure, especially pressure in one direction, by putting something lubricative on the outside of the case provided room to release the bullet exists.
Top authorities of the recent area don’t support the idea; the referenced Varmint Al study also thoroughly refutes it, the conclusion being even highly improbable polishing of the chamber and lubrication of the case cannot increase “thrust” on the bolt to levels the rifle cannot stand.
The point that case lube used with with the military arms did not increase “bolt thrust” to dangerous levels is self evident. If lube increased bolt thrust to dangerous levels the guns that oiled the cases would have never lasted through trials to be accepted into service. Oiling cases is undesirable for reasons including that of dirt ingress, but bolt thrust increase is not among them.
I might add the some of the most improbable suppositions on this topic could be avoided if the people postulating on the topic attempted to answer a simple question.
If physical gas law says pressure in a closed vessel is the same in all directions, and it is, how is it possible to multiply the force exerted in one direction when pressure must be the same in all directions? The only thing that is acting is pressure, nothing else.
A further refutation of Hatcher:
Recall just why competitors that had problems were greasing their cartridges, and where. The intent was to reduce the cupronickel jacket fouling of the barrel using the bullets of the era. The competitors were daubing grease on the bullet and neck area. Of course a bottlenecked case will tend to pack grease in this area when done repeatedly. Problems are not hard to see developing after repeatedly so doing, but bolt thrust increase was the wrong answer to the puzzle.
Thus the observation of nearly ninety years ago promoted a mistaken cause and effect that exists in folklore in erroneous supposition to this day.
Hatcher could have avoided making the mistake that supposing bolt thrust was the cause had he remembered the physical principles governing how pressure is exerted in closed containers. PO Ackley could have realized his case shape reducing bolt thrust idea was in error had he pondered on the tensile strength of cartridge brass.
It is easy to criticize with hindsight, but to correct errors in determining cause and effect hindsight is all we have. Someone has to promulgate an incorrect idea before it can be explained to be wrong. No smear is intended on two men who had such a great influence on firearms in this country. But at the same time nobody is perfect.
It is also somewhat ludicrous to assume that the designer of a firearm figures that the bolt of the gun by design has to contain less pressure or force than the chamber walls. Pressure is the only force exerted.
Stating that a gun relies on a brass case with a tensile strength far lower than the steel the gun is made from to “save” the gun or risk “damaging it” if said weak case does or does not grip the chamber is pretty obviously a nonsensical statement and a clearly false examination of the issue.
Guns are designed under the assumption that the full rated pressure of a correctly loaded cartridge will be contained when said pressure is exerted in all direction as physics says it must. Including the full rated pressure in the rearward direction.
My understanding----The cartridge is fired. In a dry/clean chamber, the cartridge wall grips the chamber momentarily, causing a nano-seconds delay before the case is slammed back against the bolt-face. This, albeit slight delay, allows pressure to begin to drop, thereby minimizing the force of the backward thrust of the case against the bolt-face. My belief is that describing an oil generated chamber insult as somehow being a massive increase of pressure, is simply wrong. It is not that a one time “wet” chamber or a single oily cartridge is going to blow your firearm up, rather damage can occur “long-term” from repeated insult to the bolt-face/locking lugs. As an example, the 303 British cases are infamous for separating just ahead of the case-web. I would ask you to consider that when forming 303 brass to fit an individual chamber, a light coating of lubrication usually prevents (or at least delays) case failure due to the dreaded separation just ahead of the web. These cases so formed will last considerably longer before separation as long as they are only neck-sized after forming them to that firearm’s chamber. If, on the other hand, cases are full length reformed after each firing and dry-fired, case separations will rather quickly occur. I am just an old country boy, don’t know much either, but I have and will continue to err on the side of caution and limit using lubed cases as much as possible.
R.D.M.
I don’t lubricate cases either but not because I think the gun will fail in so doing.
The error is in thinking a flimsy brass case shields a set of bolt lugs specifically designed to hold against such pressure from damage. If pressure is high enough to stretch a case, that full pressure is delivered to all parts of the chamber.
The case stretches to touch the bolt face long before pressure peaks due to the fact that brass tensile strength in most rifle cartridges is much lower than peak chamber pressure, so the “delay element” to “shield” the bolt from peak pressure does not exist. The bolt sees whatever pressure the rest of the chamber sees in any practical analysis.
The yield strength of brass is far less than the working pressure of most rifle cartridges, and there is no significant attenuation of pressure on the bolt by the movement of the brass as pressure peaks.
This is rather like claiming lining the interior of a safe with an expandable balloon by placing it in a certain orientation and setting off a small bomb inside somehow reduces the force on the safe interior in only one direction (where the door is perhaps) and makes it more resistant to damage in that one direction.
A weak low strength lining does not reduce the pressure forces in a unidirectional way in a closed container. Pressure is the only force present.
303 case separation has much to do with cases that poorly fit chambers. We appear to agree that lubricating the case to prevent separation when forming the case does no harm to the rifle.
As I said, as long as the pressure did not exceed rifle design whether the case grabs or not will cause no harm.
Last edited by 35remington; 09-15-2019 at 06:52 PM.
I can't prove this but I believe a case moves to the bolt before it seals to the chamber. The case is relatively light and as soon as the pressure rises enough to push it away from the bullet it scoots to the bolt. I don't know how much pressure it takes to release the case from the bullet but it can't be much, maybe a few hundred psi. As soon as the pressure is high enough to separate the case from the bullet the case will move the .001/.002 to the bolt. I believe the release pressure is much less than what it takes to seal/stick the case to the chamber. I have seen blackened cases when shooting relatively low pressure loads. Apparently these blackened cases are caused by blowback because the cases haven't sealed completely to the chamber. This makes me think it takes a substantial amount of pressure before the case sticks to the chamber giving the case plenty of time to move to the bolt and then push the front of the case forward. Also straight wall cases don't seem to stretch like bottle neck cases. I believe this is because there is little to push forward. If cases stuck to the chamber and then stretched to the rear, straight wall cases would stretch as badly as bottleneck cases. And no, I don't believe oil on a case has any affect on bolt pressure
Some stress analysis of Rifle Chamber Finish & Friction Effects on Bolt Load and Case Head Thinning here. Interesting read.
http://www.varmintal.com/a243z.htm
If does correctly identify that the case acts as a piston in a cylinder and how it is affected by friction and the ultimate affect on the force of movement that the case (piston) has on bolt loading.
Last edited by M-Tecs; 09-24-2019 at 12:09 AM.
2nd Amendment of the U.S. Constitution. - "A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."
"Before you argue with someone, ask yourself, is that person even mentally mature enough to grasp the concept of different perspectives? Because if not, there’s absolutely no point."
– Amber Veal
"The Highest form of ignorance is when your reject something you don't know anything about".
- Wayne Dyer
The thought is that a lightly lubricated case allows the case to expand more evenly with less possibility of creating a thinned spot in the brass. Without actually testing its hard to tell if and how much it makes a difference. I do give is some credibility based on the following example.
When I first start shooting NRA Highpower two of my buddies were using State Association M-14 DCM rifles. Both rifles had excessive head space. They would complete head separate LC brass on the 3rd fire about 50% of the time. Surprisingly both pieces would always eject. My buddies put thousands of round thru those rifles at a minimum and they had hundreds of head separations.
They started lightly oiling the cases and they would get one or two more loadings out of the case.
When forming 22-225 AI, 240NMC, 6XC and 243 AI when I lube the case I tend to get just a little better results. When I formed 6XC from Winchester brass the differences in the sholder forming completely was noticeable.
Last edited by M-Tecs; 09-23-2019 at 04:33 PM.
2nd Amendment of the U.S. Constitution. - "A well regulated Militia, being necessary to the security of a free State, the right of the people to keep and bear Arms, shall not be infringed."
"Before you argue with someone, ask yourself, is that person even mentally mature enough to grasp the concept of different perspectives? Because if not, there’s absolutely no point."
– Amber Veal
"The Highest form of ignorance is when your reject something you don't know anything about".
- Wayne Dyer
I think a lot of what you say is correct.
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