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Thread: Case head separation

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    Default Case head separation

    So a few days ago I responded to a thread and I think I may be wrong in my thinking. I said I believe the brass sticks to the front of the chamber upon firing because of pressure and then the thick non expanding head of the case pushes to the bolt and stretches the case where the thin part of the case meets the head. Then I got to thinking about straight wall cases and revolvers vs bottleneck cases. Straight wall cases don't stretch much nor is there a problem with case head separation. It would take very little pressure to push the case to the bolt face. Maybe only 50 or 100psi, which is way below brass expanding to grab the chamber wall. If that is true, then we would get no stretching of straight cases and lots of stretch and blow out of high case capacity small bore cases. This would also account for why bottle neck cases don't work well in revolvers. At high pressure the steel of the gun expands a little and then retracts to it's original size where the brass expands to fit the expanded chamber but does not shrink back quite to it's original size and becomes hard to extract. This leads me to believe there is little problem with very small amounts of lube left on a case from sizing. If you put enough grease/oil on a round it would be possible for the oil to be forced forward ( around the neck area) as the case expanded to prevent the neck from expanding and raising pressure of the fired round. I believe bolt face pressure will be the same as the interior of the case whether the case is lubed or not. I know there are some of you out there that know a lot more about this than I so, am I guilty of fuzzy thinking or am I on the right track?

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    Quote Originally Posted by rbuck351 View Post
    ...I believe bolt face pressure will be the same as the interior of the case whether the case is lubed or not. I know there are some of you out there that know a lot more about this than I so, am I guilty of fuzzy thinking or am I on the right track?
    I don't believe I know more about this than do you... Neither do I believe a tiny amount of residual case lube will have any discernible affect in a chamber.
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    I have been looking into this a lot lately. I read that passage in Smittyís book the other night. At this point I believe the writer is correct that lube (he is talking about oils in the book BTW) can increase pressure on the bolt face. But am also convinced he is all wet about how and why that would be, it has nothing to do with cases not sticking. He brushes with the truth but doesnít quite grasp it so canít explain it.
     
    Lube between the chamber wall and case will get extruded (squished) to the front and back of the chamber but mostly to the front because of the shape and relative strength of the bottleneck case, acts a bit like a piston driving it forward. At the front of the chamber it will find the end of the chamber cut and need to make a double 90* S turn to enter the space around the bullet. Fast moving things donít like to turn 90* corners so we are going to have a pressurized backup here constricting the neck around the bullet.
     
    Now, if there is enough lube/oil then the case neck could be constricted by a force just about the same as the force trying to move the bullet down the bore. This would definitely increase chamber pressure until something gives Most likely the bullet givs at some point but if enough pressure builds before that . . . Well KABOOM.
     
    So sure it can increase bolt face force but not just the bolt, it would increase the force on everything. How much lube/oil/liquid would it take? Well there must be enough to flow but it seems not as much as you would think at first glance. How much does it take to fill the void around the case neck for about .050Ē of its length? That ainít much volume at all but that would certainly be enough to be a problem to some degree.
     
    I donít think residual sizing wax or lube from reloading left on would be a safety issue unless you are unusually sloppy with it, there needs to be enough in there to flow. If sloppy enough it could (and apparently has) buildup in a chamber to the point it becomes a safety issue. But as an accuracy issue I think it is surely a significant thing long before a safety issue as it could give inconstant bullet pull and you just think itís a bad load, flyer, flinch or whatever.

    So my conclusion is that itís bad practice to leave excess lube on the case but there is no need to make them hospital clean ether. In other words I keep doing it the way I always have.
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    Andy, the only time i had a problem of the sort was with a 223 on a prairie dog hunt. My cases had been lubed with the old roll them on a pad method, RCBS lube was used. I was in a hurry and didn't get them wiped off good. It didn't take long until I had cases sticking and had to knock a couple out with a ram rod. Finally cleaned the chamber with a copper remover and got chunks of crud out of that chamber that looked like dried varnish. I never had any case separation issues though.

    Now-a-day I only use spray on lubes(other than when reforming brass like making 256 brass out of 357s, that takes more than a spray on lube) and then tumble them in a bath towel for a little while after sizing and never have any issues. I took a couple of terry bath towels and had mother sew up the sides to make bags out of them. I dump sized brass in them put a zip tie around the top and throw them in the clothes dryer on tumble only for a half hour. I'm lazy though

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    To add to what Andy said, and I apologize if I missed you saying this, I read quickly. Excess lube, or any foreign material is going to reduce the chamber dimensions and up the pressures where thousandths of an inch are significant. I think the greater contributor to case head separation is resizing too much, pushing the shoulder back more than necessary. The more the shoulder setback the more the ends of the case are going to be allowed to move away from each other with each firing, which is why I resize as minimaly as possible while still allowing for reliable functionality.

    Also, I think everyone who has any reloading experience has encountered what Andy was explaining about the case lube being forced throughout the chamber under pressure, but rather than a chamber, the resizing die instead. Get a little too much lube on a case, run it into the resizing die and extract only to find that a spot on the shoulder has collapsed, and this happened under compartively low pressure and low speed, yet the excesss lube could not spread out fast enough, nor thins enough not to damage the case. Looking at it this way might actualy have the reverse effect and prevent, or reduce the amount of stretch in the case due to the smaller dimension of the chamber per the space occupied by the excess lube, but could contribute to sticky extraction by the change in the lube under heat and pressure.

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    I didnít cover the tight chamber effect but it is surly there.
     
    The shoulder dents from reloading dies are a good example. In firing the case is full of pressure so rather than denting the shoulder the shoulder will act like a piston and drive the lube up into the neck aria.
     
    The piston effect I think is the case killer, driving the shoulder forward while the head is driven back. I donít know if the head moves back first or shoulder moves up first but the result would be the same, thinning of the case wall near the head where it is thinnest anyway. But if there is excess lube/oil in there it is going to be driven forward and back from that thin spot, the first place to expand. Then get pushed up to the shoulder area as the case expands outward. Then the pressure shoves that stuff at the shoulder forward to the neck area like a piston pump.
     
    Revolvers donít like bottlenecks because they fill the chamber completely and wedge lightly against the frame. The shoulder means the case canít slide back forward away from the frame and let the cylinder rotate freely. To rotate a revolver cylinder the case head moves sideways against the frame but to open a rifle bolt the bolt just rotates around the center axis of the case. Iíve been pondering a way to make the 256wm work in a revolver but so far I come up with very little. Best I have come up with is a bigger bushing around the firing pin to reduce the length of the fired chamber so fired cases could rotate freely around the rest of the frame . . . No idea if would work well enough.
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    I can't see anything wrong with the Original theory that was brought up.

    (Lubed cases, fail to stick to the sides of the chamber, and there is increased pressure on the bolt face.)

    In the other thread, I only brought up, and later researched, the Gun Blowups, that were concluded to be due to lube or grease on the necks, to support that Original primus.

    No-one is saying that every rifle with a greasy chamber or cartridge will BLOW UP, but just that it can cause problems depending, on the particulars.

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    Quote Originally Posted by elmerkeithclone View Post
    Andy, the only time i had a problem of the sort was with a 223 on a prairie dog hunt. My cases had been lubed with the old roll them on a pad method, RCBS lube was used. I was in a hurry and didn't get them wiped off good. It didn't take long until I had cases sticking and had to knock a couple out with a ram rod. Finally cleaned the chamber with a copper remover and got chunks of crud out of that chamber that looked like dried varnish. I never had any case separation issues though.

    Now-a-day I only use spray on lubes(other than when reforming brass like making 256 brass out of 357s, that takes more than a spray on lube) and then tumble them in a bath towel for a little while after sizing and never have any issues. I took a couple of terry bath towels and had mother sew up the sides to make bags out of them. I dump sized brass in them put a zip tie around the top and throw them in the clothes dryer on tumble only for a half hour. I'm lazy though
    It doesn't sound like a mystery to me, if one accepts that the lube, causes the neck to be unable to expand and release the bullet as easily. This resulting in higher pressure, and hence the sticky extraction.

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    What I'm thinking here is that If the case stuck to the chamber wall before being set back to the bolt face, then straight wall cases would have head separation just the same as bottleneck. This leads me to believe that the case slams to the bolt face before sticking to the chamber wall thus bolt face pressure remains the same whether the case is lubed or not. If enough lube were left on the case it could prevent the case from releasing the bullet and this could raise pressure or build up over time doing the same thing. But, I am now convinced that the case sticking to the chamber wall happens after the case has set against the bolt face.
    No doubt excessive resizing leads to case head separation and I size only far enough to keep from setting the shoulder back. Actually I stop sizing about .020 from the shoulder which leaves a little belt that fits the chambers neck area and helps center the case in the chamber. I used to size 7MM mag cases till the die completely stopped against the shell holder and ended up separating a few cases at the head. It seems the most belted case dies set the shoulder back more than needed.
    I don't think it's a good idea to leave much lube on the case but I don't think it needs to be hospital sterile either.
    I have a 92Win in 25/20 that gets shot a bunch with lead bullets and cases that are not completly free of lube and rarely ever gets the barrel/chamber cleaned because it's not easy to clean and I'm lazy. It has never given a hint of problem.

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    Quote Originally Posted by rbuck351 View Post
    ...I size only far enough to keep from setting the shoulder back. Actually I stop sizing about .020 from the shoulder which leaves a little belt that fits the chambers neck area and helps center the case in the chamber.
    I do exactly the same.

    Has anyone read last month's Handloader wherein Barsness wrote about measuring bolt face peak pressure using pressure sensitive film?
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    Quote Originally Posted by rbuck351 View Post
    What I'm thinking here is that If the case stuck to the chamber wall before being set back to the bolt face, then straight wall cases would have head separation just the same as bottleneck. This leads me to believe that the case slams to the bolt face before sticking to the chamber wall thus bolt face pressure remains the same whether the case is lubed or not. If enough lube were left on the case it could prevent the case from releasing the bullet and this could raise pressure or build up over time doing the same thing. But, I am now convinced that the case sticking to the chamber wall happens after the case has set against the bolt face.
    No doubt excessive resizing leads to case head separation and I size only far enough to keep from setting the shoulder back. Actually I stop sizing about .020 from the shoulder which leaves a little belt that fits the chambers neck area and helps center the case in the chamber. I used to size 7MM mag cases till the die completely stopped against the shell holder and ended up separating a few cases at the head. It seems the most belted case dies set the shoulder back more than needed.
    I don't think it's a good idea to leave much lube on the case but I don't think it needs to be hospital sterile either.
    I have a 92Win in 25/20 that gets shot a bunch with lead bullets and cases that are not completly free of lube and rarely ever gets the barrel/chamber cleaned because it's not easy to clean and I'm lazy. It has never given a hint of problem.
    There is quite a difference in pressure max, betwixt most Straight Wall and Bottle Neck cartridges. Also, the straight wall cartridges have much higher expansion ratios. Maybe that makes a difference.

    I can accept the following explanation for what happens on firing a bottle-neck cartridge...... [The case moves forward with the firing pin blow, and when he powder is ignited, the case expands and the sides of the case stick to the sides of the chamber, and the case head expands back, (rather than moves back) against the bolt face and flattens the primer. ]

    I have had the opposite experience with 7mm RM sizing. If I FL resize the cases (using either of my 2 different manufacture sizing dies, I can barely get them sized enough to fit the chamber. Plus, it's like an ordeal to do it. Same, with my other belted case rifle, 7mm Weatherby.

    What happens as near as I can tell, is that when the shoulder is contacted by the sizing die, it is squeezed and the shoulder moves forward, and then has to be set back AGAIN, enough to allow the case to chamber.

    It is not possible to set the shoulder back too far, on either. It's difficult to get the shoulder back ENOUGH.

    I'm thinking it is the chamber dimension that makes it so.

    Fired cases fit the chamber just fine. I've solved the problem by using Neck Only sizing dies.

    There exists, the theory that you can get better fireforming if you deliberately lube cases. I would not do that, unless I reduced the load to quite a bit less than maximum load.

    IIRC, the 303 British was a cartridge that benefited from this method, because it is one that can stretch because there is some give in the action.

    I don't recall more, and have no idea where I would look it up.

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    I haven't read that article but it would be an interesting read especially if he compares lubed vs non lubed cases.

    I believe the pressure to move a case to the rear of the chamber is a LOT less than the pressure required to expand the brass far enough to lock it to the chamber walls. I really believe that by the time the brass has released the bullet the pressure is way higher than it takes to push the brass to the bolt and still way lower than it takes to grab the chamber walls. Think of this in slow motion. As the brass is expanding just enough to release the bullet the brass now jets to the rear before the brass has expanded to the chamber walls. Pressure is still rising and if it gets high enough, will seal the chamber and stick to the walls. If there is a shoulder, it will now blow forward to fill any head space. I am sure the pressure required to push a case to the bolt is a LOT less than the pressure required to expand brass to the chamber sticking point.

    My 454 Casull runs at about 62,000 psi and it doesn't have problems with brass growing in length or case head separation. It also doesn't have a shoulder to push forward to stretch the brass. But, if the case was forward stuck to the chamber wall, it would certainly blow the head back to the bolt face causing head separation after a few rounds. It also uses a much faster powder (H110 or LIL,Gun ) than a bottleneck rifle round, which would give the brass even less oppertunity to move to the bolt face before sticking to the walls.

    I believe all this happens before much if any bullet movement happens which would leave out expansion raitos.

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    Quote Originally Posted by Smitty of the North View Post
    I can't see anything wrong with the Original theory that was brought up.

    (Lubed cases, fail to stick to the sides of the chamber, and there is increased pressure on the bolt face.)
    Smitty of the North
    I do, the inverse of that would be that dry cases stick to chamber walls and decrees bolt face thrust. The premise is that the case is what contains the pressure and somehow holds some force off the bolt face. But we know the brass case canít withstand the pressure, they have a 100% fail rate when not supported by a chamber. So it doesnít matter to bolt face thrust if the case sticks to the walls or not, ďXĒ amount of pressure in the chamber will give you ďYĒ amount of bolt face thrust . . . Directly proportionate to the presure and surface area of the bolt face because the brass is pushed about 5 times past the pressure load it can structurally hold.
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    Quote Originally Posted by ADfields View Post
    I do, the inverse of that would be that dry cases stick to chamber walls and decrees bolt face thrust. The premise is that the case is what contains the pressure and somehow holds some force off the bolt face. But we know the brass case canít withstand the pressure, they have a 100% fail rate when not supported by a chamber. So it doesnít matter to bolt face thrust if the case sticks to the walls or not, ďXĒ amount of pressure in the chamber will give you ďYĒ amount of bolt face thrust . . . Directly proportionate to the presure and surface area of the bolt face because the brass is pushed about 5 times past the pressure load it can structurally hold.
    .
    I concur. I think pressure exerts equally in all directions and onto all surfaces within the chamber. Pressure measurement tests I've read about seem to corroborate that. Seems like we're going to rehash the same things that were already hashed in the other thread...
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    Quote Originally Posted by rbuck351 View Post
    I haven't read that article but it would be an interesting read especially if he compares lubed vs non lubed cases.

    I believe the pressure to move a case to the rear of the chamber is a LOT less than the pressure required to expand the brass far enough to lock it to the chamber walls. I really believe that by the time the brass has released the bullet the pressure is way higher than it takes to push the brass to the bolt and still way lower than it takes to grab the chamber walls. Think of this in slow motion. As the brass is expanding just enough to release the bullet the brass now jets to the rear before the brass has expanded to the chamber walls. Pressure is still rising and if it gets high enough, will seal the chamber and stick to the walls. If there is a shoulder, it will now blow forward to fill any head space. I am sure the pressure required to push a case to the bolt is a LOT less than the pressure required to expand brass to the chamber sticking point.

    My 454 Casull runs at about 62,000 psi and it doesn't have problems with brass growing in length or case head separation. It also doesn't have a shoulder to push forward to stretch the brass. But, if the case was forward stuck to the chamber wall, it would certainly blow the head back to the bolt face causing head separation after a few rounds. It also uses a much faster powder (H110 or LIL,Gun ) than a bottleneck rifle round, which would give the brass even less oppertunity to move to the bolt face before sticking to the walls.

    I believe all this happens before much if any bullet movement happens which would leave out expansion raitos.
    Your theory seems valid to me, itís very hard to know what happen when in there.


    I have 460S&W brass that got overworked at the neck from the expand/crimp of reloading, it was cut to 454 and worn out there, then cut to 45 Colt. Still going strong as hot 45 Colt brass and not any signs of head separation. But in 357 brass I have seen the occasional case head separation over the years, some of that brass has put a lot of lead down range. I have gotten 3 of the dredged horizontal cracks so far in 357 that I necked to 256wm, add a bottleneck and the rate goes way up.
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    Quote Originally Posted by ADfields View Post
    I do, the inverse of that would be that dry cases stick to chamber walls and decrees bolt face thrust. The premise is that the case is what contains the pressure and somehow holds some force off the bolt face. But we know the brass case canít withstand the pressure, they have a 100% fail rate when not supported by a chamber. So it doesnít matter to bolt face thrust if the case sticks to the walls or not, ďXĒ amount of pressure in the chamber will give you ďYĒ amount of bolt face thrust . . . Directly proportionate to the presure and surface area of the bolt face because the brass is pushed about 5 times past the pressure load it can structurally hold.
    .
    The case DOES hold the pressure, because it is supported by the chamber walls and the bolt face. When it fails, it leaks the pressure.

    Reportedly, straightER walls in some case designs, like the AIs result in longer case life. Straight cases don't have the shoulder that moves forward, effectively causing the case to back up. AND, cases with more taper are more prone to back out, but in any case, they do stick. (Except, not as well, if there is some kind of lube on them.)

    Obviously, the case sides don't stick to the sides of the chamber walls until the pressure is high enough. Where in the pressure time frame, that would be, I'm sure, is a variable.

    Lube anywhere in the chamber, from any source, takes up volume and changes the pressure all through the curve.

    It can be problematic for the bullet release, which can also change pressure during the curve.

    Isn't case separation a function of excess headspace? And, NOT an indicator of WHEN the case moves back towards the bolt face?

    Doesn't expansion ratio effect how fast the powder burns in any cartridge? High Expansion Ratio cartridges use faster powders.

    If the pressure on the bolt face is increased, it doesn't need to be noticeable, to be there. Same with a tiny bit of lube left on the brass case, although, Rinker said that it takes VERY little to increase the pressure.

    WHEW!

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    The case only acts as a gasket, it isnít holding the pressure the chamber is because with no chamber there is a 100% fail rate of cases . . . Even without a bullet 100% fail.
     
    Excess headspace means too much room, too long a chamber. That can mean too long in front or back, it doesnít matter which for case life because ether way the case can not hold back the pressure and will stretch at the weakest point until filling the chamber. If it canít stretch that far it will rip and if ripped in the wrong place will leak just like blowing a gasket leaks.
     
    Yes anything taking up room in there will increase pressure and thereby force on the bolt face . . . And every other part of the chamber too. The force is everywhere in the chamber is equal due to the pressure applying equal force in every direction, the amount of surface area itís pushing on dictates the force applied to the bolt. The surface area of the bolt face portion doesnít change no matter how oiled up the chamber is, only the pressure in there applying the force to everything changes.
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    Ya know, this is a really good discussion. It makes you think a little. In the other thread, I said the ejector (for spring loaded plunger ejectors) pushed the case forward a little and the firing pin, when fired, pushed the shoulder (bottle neck cases) against the forward part of the chamber. Typically, we are talking only a few thou in head space and many of us only push the shoulder back a couple of thou. You neck sizers, also do this occasionally. So... back to inside the chamber... I said that when ignition occurs it pushes the bullet forward and the case back and outward, stretching the the fore part of the case near the shoulder. Hornady's description is different and they are probably right. They say the case presses against the chamber wall and the case head/web stretches back against the bolt face.

    http://www.hornady.com/ballistics-resource/internal

    Now, I suppose, if your cases were too "slippery" from left over lube, they might slide back, like I originally postulated, and the fore portion of the case would stretch and not the web.

    As I read it, there is some concern that any amount of lube left on the case inhibits it from gripping the chamber wall and leads to greater pressures on the bolt face and bolt in general. I can understand the reasoning behind that, but I just don't buy it. When the explosion occurs inside the case, pressure is exerted in all directions. The chamber wall, bolt lugs and receiver lug surfaces all contain those forces, leaving one exit. If we conclude that a slippery case would slide back with more pressure against the bolt face, then we must also conclude that the case itself also contains those forces. Case head separation is a good example of why that isn't the case The brass fills the gaps where ever they are because it is mailable and fluid. Sooo... it matters not if the brass slides or not... at some point it will stretch in whatever direction, to fill the voids, and the engineering of the bolt, lugs and chamber will contain the forces... within specs.

    As some of you know (especially Smitty), I like to run my loads near the ragged edge. And I've loaded them completely dry as well as with some residual lube and i have just not detected any difference between the two. If dry cases contained pressure better, then theoretically, I could load higher pressure loads with dry cases, and, if I maybe scuffed the case walls up a little with a scotch pad, I could load them even hotter.

    Now there are some better quality, stronger brass cases that can hold pressure a little better than the standard RP or FC, Lapua being a good example.

    As far as "any" amount of lube taking up space in the chamber, no one could even measure the thickness of lube I use on a case, and then I wipe 90% of it off. So the hydraulics is not a factor. I can see were excess grease or whatever, might cause pressure problems, depending on the amount and how tight the chamber, especially the neck, is.

    So I am curious, how do you all lube and size and ry your case off? Do you get them completely dry?
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    Quote Originally Posted by MontanaRifleman View Post
    So I am curious, how do you all lube and size and ry your case off? Do you get them completely dry?
    Well I can tell you from rust bluing wax and oil are very hard to truly remove. You think you have it with tons of alcohol, brake spray, acetone or whatever and it still gets you! A the minuet boil in dish soap water seems to do it . . . Put in what you think is a clean part and get reedy to be amassed whatís about to be floating on the water!
     
    With ammo I use One-Shot for normal loading or Impearl for forming or FL sizing of big cases. I apply them to the case and the die and donít make any effort to ďremoveĒ ether of them. I apply a lot of spray and very little wax and they seem to get removed through normal handling with no more than I use in the first place. Iíve handled a lot of Smittyís loads, they are spiffy clean but I donít think anyone could tell my non wiped-down rounds from his wiped-down loads from factory loads other than by color of the older brass.
    Andy
    On the web= C-lazy-F.co
    Email= Andy@C-lazy-F.co
    Call/Text 602-315-2406
    Phoenix Arizona

  20. #20
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    Apr 2006
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    SwampView AK, Overlooking Mt. Mckinley and Points Beyond.
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    I agree, it's a good discussion, and educational, too.

    I'm glad that you mentioned the Plunger type Ejectors. So many rifles have that mechanism. Most folks fail to consider it, when talking about headspace, etc. Of course, it would fully compress when the case expands backwards, but the plunger would likely be holding the case forward after chambering.

    Would there be sich a thang as case head separation without the case sticking?

    I don't know how much lube on the case it takes to cause a problem. I think if you wipe it off, you're good to go.

    Rinker didn't mention scuffing up the case walls but he did say that the chamber walls shouldn't be too smooth/polished. Surely, the same would apply to the brass.

    When I Neck Size my 7mm Mag. I don't use ANY lube. The neck is so SHORT, and if I brush out the Inside Neck, the expander passes smoothly, and effortlessly.

    I like to lube brass with One-Shot because some of the spray can be put inside the neck. Otherwise, I apply lube inside the necks with a Q Tip. Any time the expander doesn't come back up through the neck easily, the Q Tip allows you to put some on the inside shoulder of the neck, as that's where it's needed.

    I wipe lube off the outside with a cotton cloth or a paper towel, and wipe the Inside Necks with a cleaning patch on a cleaning loop, changing it when it gets dirty.

    Just the other night I used those Hand Wipes, and it must have done a pretty good job, as the wipes sure got doity.

    Smitty of the North
    Walk Slow, and Drink a Lotta Water.
    Has it ever occurred to you, that Nothing ever occurs to God? Adrien Rodgers.
    You can't out-give God.

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