FireForming Brass and oil lubricity

[Slamfire]

I was reading the May 2013 article “Fireforming Brass” by John Barsness from Guns Magazine, and I am a bit confused by this statement:



If the headspace is a little long but cases will still fire consistently, oiling the case will allow it to slip rearward without stretching. No, this doesn’t increase bolt-thrust. Any suitable oil loses its lubricity at pressures below 10,000 psi. Once pressure rises to 10,000 psi, the case grips the chamber wall firm.

https://gunsmagazine.com/fireforming-brass/

What I am confused about is the “loses its lubricity at pressures below 10,000 psia”, I think he means above 10,000 psia, but if it is above, what happens between the case and chamber above 10,000 psia? Does the case lock in? I have been looking on the web for information to find if at high pressures “oil loses its lubricity” but I have not found anything to verify this. Anyone know?


I did find this historical account from General Thompson, the inventor of the “Tommy Gun” . This sort of supports the idea that something happens at high pressure with oil. General Thompson's early designs must have relied on oil for the “Blish effect” to work. His later design used dissimilar materials: the bronze locking wedge in a carbon steel incline, where the wedge was fixed in position at high pressure. I have attached pictures of this incase someone has never seen this locking mechanism.

From Arms and the Man 1 Nov 1920

“John Thompson’s surprise Party” by Capt E. C. Crossman

General John Thompson:

So the submachine gun was fitted out with felt oil pads in the rear of the receiver housing, over which or by which the bolt slides at each stroke. The “gun crew” has nothing to do with the oiling beyond squirting some more into the pads every 500 rounds or so. …

The locking bolt is the working out of a theory which I have followed for some years with much interest. Some years ago, trying to blow up a Winchester Model 1886, one of the best and most popular of the lever action type, I found much to my surprise that the bolt would unlock, and would back out of the length of the shell in firing. The conditions permitting this, were, the removal of the lever catch on the tang, and second the oiling of the cse, combined with an action pretty old and worn smooth and free of extra friction.

The gun did not blow open, it did not open under heavy pressure, it was entirely safe so far as that is concerned. It unlocked when the pressure was nearly off, and the bolt slid gently open, taking the fired case with it.

I wrote up this peculiarity, and a Navy Officer, Commander Blish, called on me, and discussed the matter. It developed that he had found by experimental work, combined to a few cases of inexplicable opening of the breech bolts of big guns, firing blank cartridges that any arm which has a bolt cammed entirely shut, as by a locking bolt of the type the M1886 referred to, is likely to cam itself open again when the breech pressure falls enough to “unlock” the friction surfaces the locking bolt in its grooves in the receiver and breech bolt.

[Brian Pfleuger]

I think he means that the point that they lose the lubricity is below 10,000, like 6 or 8,000, for example.

I'm pretty sure he's wrong about it not increasing bolt thrust. I fireformed some cases in my 243AI and I still had some oil in the chamber. The extractor marks were scary and went away completely as soon as the oil was removed.

I've heard his theory in several places but I'm not convinced it's true and my experience tells me it's not.

I think the best way to fireform cases is to jam the bullet in the lands, which forces the head against the breach, and use starting loads or loads that generate at least 30,000psi, as appropriate for the cartridge.

[BumbleBug]

I recently bought a heavy 7x30 Waters contender carbine barrel to replace a light weight one in the same caliber. As usual, I began with lower pressure starter loads in the new barrel using brass originally fire formed in the old barrel. Cases were full length sized with standard Redding dies. Surprisingly, about 10% didn’t fire & some of the lighter loads backed the primers out & left them well rounded. I immediately remembered that I read somewhere that slightly lubing the case would aide in Fire Forming. After contemplating this for a while, I finally realized that safety trumps dollars & ordered 100 brand-new Win cases from Bruno’s (the only place I could find brass). Using my $.50 each cases, my scarce $.05 each primers, my $.28 each Sierra bullets, & charges of some older H322 powder my new cases cost me about $.90 each! I lost only 1 case during resizing. From here on my sizing will be to a snap-fit in the contender. If I wasn’t such a penny pincher & reloading snob, I’d buy a box of Federal factory ammo & test the new barrel with it.
Since the Waters headspaces on the rim, either the Contender is a bit loose (doesn’t feel like it), my new barrel has a larger chamber or my Redding dies size a bit short. I suspect the later, which no problem for a handloader

[SL1]

When making .30 Herret cases for my Contender, I have found that they still shrink in length when fired for the first time, so long as I use modest-pressure loads for fire-forming. The cases are already sized so that the shoulder produces the "just closes easily" type fit in the chamber. But, the Contender break-open action is somewhat "springy" (especially if it isn't a G2 frame). So, after each firing, the shoulder always gets pushed foreward enough to require set-back during resizing for the proper fit.

The reason that the cases grow on the first firing is that shoulders and body need to be blown-out for minimum taper of the body, and the brass has to come from somewhere. If the case does not slip a little in the neck area then the extra brass comes from stretcing the body down near the case head where it does not expand enough to grip the chamber wall. That is the area where stretching reduces case life by starting case head separation.
So, I ususally fire-form with unoiled cases and modest loads to get the most reloads out of my cases.

Loss of length on the first firing is about 0.008" to 0.010" when forming from .30-30 brass. I usually allow for this when cutting-down my .30-30 cases, because a cast of my chamber revealed that it is long enough to accomodate somewhat over-length brass. Subsequent firings with full-power loads typically increase case length by about 0.002" to 0.004" per firing. (Contenders are notorious for short brass life with bottlenecked cases and stiff loads.)

SL1

[Slamfire]

Brian, thanks for the reply

I'm pretty sure he's wrong about it not increasing bolt thrust. I fireformed some cases in my 243AI and I still had some oil in the chamber. The extractor marks were scary and went away completely as soon as the oil was removed.

I can’t explain that unless your pressures were way above SAAMI limits. I now conduct my load development with lubricated cases as I don’t want friction between the case and chamber to disguise pressure indications. I want sticky extraction when the load is too hot. When I get a sticky case I back off on my loads. Primer indications are unreliable with dry cases. I have found, particularly in semi autos, after I started shooting lubricated cases, loads that gave flat primers with dry cases, with lubricated cases the primers were nice and round. Everything else was the same so either lubrication on the outside of the case reduced combustion pressure (ridiculous) or dry cases give false indications of primer condition. With lubed cases, as I increase the powder charge, I often see the point at which primers go from rounded to flat. This is not a 100% and sometimes loads with slightly rounded primers leak or blow primers, but I believe when I see the change in primer shape, I am getting close to a maximum load. Whenever I get a leaking primer or blown primer I know I am way past a maximum load and I cut the powder charge.

As for bolt thrust. Cases are made of brass which has a yield point around 45,000 psia (though the sidewalls of the case are about 0.05” thick and can’t hold a load more than 650 psia without rupture). Remington M1903 bolts were made out of 8620 steel with this heat treatment.

“Single quenched and tempered: carburized at 925°C (1700°F) for 8 hrs., pot cooled, reheated to 845°C (1550°F), quenched in agitated oil, 150°C (300°F) temper. 1.9 mm case depth. Core properties.”

Tensile Strength, Ultimate 189, 000 psi
Tensile Strength, Yield 149, 800 psi
Elongation at Break 11.5 %

I am not concerned about bolt thrust given that the material yield of bolt lugs are almost 3.5 times greater than that of brass. I am far more concerned about brass integrity and reducing the load on the brass.

I think he means that the point that they lose the lubricity is below 10,000, like 6 or 8,000, for example.

Is that true, that around 6000 pounds the oil is squeezed out or neutralized in some way so that the case to chamber friction dominates? I have not found any data on the web to verify this phenomena and I thought oil is incompressible and therefore there will always be a lubricating film between the case and chamber.

[eldermike]

Lubricity means effectiveness. All lubricants have pressure ratings. But zero effectiveness/lubricity would be impossible. Pressure derates the effectiveness of lubricants.

However, when brass cases are drawn or formed lubricant is used and is very important in that original manufacturing process.

Intresting idea but I think I will stick with jamming the bullet into the lands and using a fire forming load.

[SL1]

There are "high-pressure" lubricants that maintain a film between metal surfaces at higher pressures than oil can. The lubricants that we use to size brass cases are examples. Think of the two metal surfaces as being vey rough on a microscopic scale, and think of the lubricant as being forced out of the places where a "high spot" on ones side is adjacent to a "high spot" on the other side. The ability of the lubricant to "stick together" under those conditions rather than part to allow metal-to-metal contact is what you want for a high-pressure lube.

As for the effects on cartridge cases while firing ammo, I think it is more complicated. The pressure at which the lubricity effect is lost could occur at different parts of the sequence involving (1) case moving forward due to firing pin impact, (2) primer moving back to bolt face due to pressure in primer pocket, (3) case head moving back to bolt face due to pressure in case. If lubricity is maintained (on ALL case surfaces) past stage 3, then the case will not stretch.

In the situation of Slamfire seeing primers that are remaining rounded at higher pressures when his cases are lubed, it would seem that the lubrication is allowing the case to get back against the bolt face EARLIER because the pressure needs to be higher before the cases can grab the chamber wall.

I am guessing that would mean that the UNSUPPORTED part of the primer sees a little less pressure BEFORE it is pushed back into the primer pocket and receives more support on its sidewalls. So, the unsupported edges of the primer can probably expand a little less in the less-supported condition when the case are lubed, giving them a more rounded corner when pushed back into the pockets while still under (increasing) pressure. When the primers are fully reseated within their pockets and the pressure is still increasing, it seems that the pressure will have to go substantially higher for the lubed-case situation in order to make the edges expand to the point where they look sharper than they appear to be with an unlubed case. That is suggesting that the bulk of the primer edge expansion occurs when the primers are slightly out of their pockets unless the peak pressure is unusually high.

Exactly how that relates to judging PEAK pressure in the case would seem to be HIGHLY dependent on MANY factors, including the lubricant's graph of lubricity vs pressure, the roughness of the chamber, the properties of the primer cup, and maybe even the amount of camfer on the primer pocket in each case.

Since Slamfire wrote that he sometimes pierces primers with edges that are not flat when using oiled cases, the logic above seems to make sense. It is also consistent with the observation that flattened primers can appear with even low-pressure loads if the cases are not headspacing properly.

SL1

[Slamfire]

Intresting idea but I think I will stick with jamming the bullet into the lands and using a fire forming load.

Thanks for the reply. When fireforming, lets say 30-06 to 35 Whelen, I use a light load even though I lubricate the case. I don't want peening. When cases with excessively large headspace are fired they peen the action. Actually the bolt loading is an impact load, not a "thrust".

Jamming the bullet in the throat will push the case head against the bolt face and that will reduce peening.

[Brian Pfleuger]

Originally Posted by SlamFire

I can’t explain that unless your pressures were way above SAAMI limits.

I can't either, except that the oil dramatically increased the pressure against the breachface. The loads were no where close to "SAAMI" pressure, even though there is no true SAAMI pressure for the 243AI. The suggested starting loads for the AI are max loads for 243Win. I got these marks on loads that were so low that they didn't even fully form the brass.

[F. Guffey]

I am a case former, I form cases then fire, after firing a formed case I eject once fired cases. The example given: Forming 30/06 to 35 Whelan is necking up, there is nothing about the case body that changes, the change is between the case body/shoulder juncture and the shoulder/neck juncture, meaning? the neck gets longer and the case length gets shorter. Then there is that magic number when necking 30/06 cases up to 35 Whelen. the case shortens .035”. (Meaning) Using 30/06 cases for 35 Whelen and or 338/06 cases is a bad habit if the purpose of the case is to cover the chamber, I want the case to cover the chamber, I want the case to cover all the chamber possible.

When forming cases for chambers I choose the longest case available, I have no reservations about purchasing once fired cases from a range, when purchasing cases from a range I want the cases that have been fired in the trashiest of chambers, when forming cases I want cases with additional length between the shoulder of the case to the head of the case.

Protrusion, I am the fan of protrusion, when sorting cases with the Wilson case gage I want protrusion, someone had to fire the case to get the shoulder flattened against the chamber (FIRST!) and a new shoulder formed forward of the old shoulder. I am not the fan of unnecessary sizing, once the shoulder is formed of the old shoulder I apply the ‘leaver policy’ I leaver where I formed-er. To be a case former the reloader must know the length of the chamber from the shoulder of the chamber back to the bolt face. After determining the length of the chamber from the shoulder back to the bolt face it is a matter of transferring that measurement to the press, die and shell holder, again, moving the shoulder back is the easy part, knowing when to stop ‘bumping? is the difficult part.

I choose to use 280 Remington cases when forming 35 Whelen and 338/06 cases to determine the length of the chamber. The bolt of a 35 Whelen and or 338/06 rifle will not close on a 280 Remington case, the 280 Remington case is longer by .051” from the shoulder of the case back to the head of the case than the 35 Whelen and or 338/06 case. What does this mean? For the fire former? That is a lot of guessing, for the case former it is a matter of adjusting the die off the shell holder ..045” to size a case that will JUST allow the bolt to close if the chamber is go-gage length with a slight amount of resistance.

Greasing my bullets? I want nothing between the case and chamber but air, I want air between the case and chamber, not a lot of air, just a little, I would be most pleased with .0005” worth, again, I want nothing but air, I want clean air, I do not want dirt, grit and or grime with the air, I know, the case is embeddable but when my case fills the chamber I want 100% contact, nothing holds and or stops better than 100% contact so I do not want ridges or cross hatches, again, I am the fan of 100% contact between the case and chamber. And, I d I do not have a lot of air between the case and chamber the amount of time for the air to exit (get out of the way) time as a factor is reduced.

I know, bench resters, they do wonders with full length sizing, difference??? The difference between the length of their chambers from the shoulder to the bolt face when compared with the length of the case from the shoulder of the case to the head of the case is ‘NOT VERY MUCH! when compared to the chamber I load for. AGAIN, I know, I have rifles that shoot magnificent groups with new ammo and or my reloads, if it was about full length sizing and or new ammo all of my rifles would shoot magnificent groups. Unlike others I have rifles that do not like anything.

F. Guffey

[F. Guffey]

March 22, 2013, 09:38 AM #8
Slamfire
Senior Member


Join Date: May 27, 2007
Posts: 3,300 Quote:
Interesting idea but I think I will stick with jamming the bullet into the lands and using a fire forming load.

Thanks for the reply. When fire forming, lets say 30-06 to 35 Whelen, I use a light load even though I lubricate the case. I don't want peening. When cases with excessively large headspace are fired they peen the action. Actually the bolt loading is an impact load, not a "thrust".

Jamming the bullet in the throat will push the case head against the bolt face and that will reduce peening.
__________________
If I'm not shooting, I'm reloading.



I am the fan of bullet jump, I want my bullets to have a running start, I know, sounds cool, “I seat my bullet to the lands and or .002” off the lands”, Me? I do not want my bullet past the lands before it realizes it is there, I do not want my bullets to even think about slowing down or starting from a dead stop to full speed in .002” of travel, again, I am the fan of the running start.

And, again, I am the fan of cutting down on all that case travel, then there is the other bundle of information that must be disregarded, the firing pin and the story about the firing pin driving the case forward causing the shoulder of the case to be driven into the shoulder of the chamber causing the case to shorten between the shoulder of the case and case head and if the story continues we are back to peening, I want my case length to match the chamber length,

Then there is that part where it is assumed the case travels to the front of the chamber when the firing pin strikes the primer. Again, Hatcher increased the length of the chamber .080” knowing he would experience case head separation when firing the rifle, he did not have case head separation, and I have fired 8mm57 ammo in an 8/06 chamber, no stretch, no case head separation etc.. The trickey part, a friend built a magnificent 7mm wildcat, he had 4 case head seperations out of 10 firings, he used the 03 Springfield, something like Hatcher, my friend proved hatcher correct, both my friend and Hatcher were shooting and modifying the 03 Springfield.

Anyhow, he informed me I was wrong, and I said I could have told you it was going to happen before you left the shop or I could have meat you at the range and corrected the problem long enough for you to form your cases with out case head separation, and? he did not ask me ‘HOW?’

F. Guffey