Brass Separation Above Belt
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J E Custom
Well-Known Member
This IS about case head separation and what causes it and how to prevent it or at least minimize it. It is also a discussion to help the original Poster understand the cause and answer his questing.
I am still having trouble with the term aligned. If a bullet is aligned, it does not touch anything and is held in place by the neck. Free bore is there to allow the bullet to move reducing the initial pressure,before the bullet strikes the lands, not to align the bullet. good concentric necks and chambers have that job.
To answer your question Edd, NO The bullet should not be out of the neck before the bullet strikes the lands. This is the reason that good concentric load are so important to accuracy. if the case neck is not perfectly "aligned", it can cause the bullet to yaw and lose accuracy.
Also the word perfect must mean different things to different people.
As a rifle builder,it means I have to try to get everything as "Perfect"
as I can and can have NO run out of any kind. The same thing goes for my loaded ammo. Why build a custom rifle with zero tolerances and then feed it sloppy loaded ammo with poorly aligned bullets that are "Good enough".
If a person can load perfect ammo buy whatever means, That is the goal. also loading great ammo Is not easy and preventing case head separation is part loading and good Gunsmithing.
I was told that I was born with two ears and one mouth. And that I should listen twice as much as I talked. Sounds like good advice and it has served me well.
PS: I will post when and where I want to and about what I want to, at least until I get as many post as Scooterbum Has and becomes an expert like him. (Take a shot, give a shot).
J E CUSTOM
He did not mention to me what the actual measurement was. He did keep several of the fires brass to measure, but considering the circumstances and common knowledge that it will take 1-3 firings for brass to be fully formed in a chamber that is within specs, I doubt those measurements will tell much of a story.
Alex Wheeler
Well-Known Member
Alignment of the bullet or case will come from the places with the least clearance around them. So unless your necks are fitted to the chamber with less clearance than the bullet has in the freebore diameter the guidance on the front end comes from the bullet in the freebore. Usually less than .00025" per side. If we could build a perfectly straight full length sized round and it was resting in a chamber it would have 2 points of contact. The side of the bullet in the free bore and the back end of the case about .150" from the base.
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bigngreen
Well-Known Member
In this case where the guage functions of the belt not the shoulder and that area of the case does not stretch you have to use the guage to verify headspace, on a beltless case where the guage and datum are on the shoulder you can get some rough measurements using fired cases.
Not all guages are equal either, I have one set from two manufactures that one is on the right side one loose while both are in spec so having an actual measurements is more useful.
J E Custom
Well-Known Member
This is where we disagree with each other, (Which really does not matter) and as I have said. I don't want the bullet resting on anything and same goes for the case. If it is not centered it is not acceptable To ME and if that's ok for others, fine.
Depending on the cartridge design and its intended use, Freebore diameter is .0004 to .0025 larger than the bullet diameter. The .0004 to .0005 requires very careful loading and is paramount in my opinion. The best case scenario Is to have the bullet centered in this space, not touching one side or the other looking straight down the center of the bore. turning the neck and carful sizing will accomplish this and the use of a concentricity gauge will verify this. And if the case is a perfect fit in the chamber and against the bolt face where it cant move.
Another downside to having a loose fit in the chamber aside from any head space is when a case doesn't fit the chamber and when fired, it can cant the case head when fired and cause uneven web stretch even if very slight and over time start case head separation This is common on loose cases and excessive head space. One easy way to check for this phenomena is to take a fired case and load it into the chamber, If this occurred, it doesn't wont to chamber the same in most positions except where it was when fired and bolt closing will be different depending on the head stamp position of the case.
On semi auto firearms, these clearances must be enlarged in order to function correctly and normally brass life and accuracy are not the prime requirements as long as they are expectable. case head separations are not expectable in combat situations or dangerous game hunts because they will prevent the use of the weapon and its usefulness At the worst time. And also it is normally not a concern because the cases are not re used and the field gauge that limits the amount of head space in these weapons determines the rejection of this weapon for use while allowing the round to be chambered and fire under the worst conditions.
This is also why most cartridges for combat use are sized to small base dimensions Like the belted case body's are also smaller than required in order to chamber with little if any effort in a poorly maintained/cleaned chamber. But the belted cases can maintain head space even with the case body grossly undersized, This can lead to work hardening and case head separation if not minimized.
Another question was ask about the shoulder angle contributing to less chance of case head separation. Yes it does. The 40o shoulder appears to all but eliminate case head separation by controlling case lengthening. When sized properly, the cases with a 40o shoulder seem to grow very little in length. I have cartridge cases that have been loaded 8 to 10 times and have been annealed 2 to 3 times that have not changed length from the original trim length enough to re trim.
This means little if any brass thinning and the risk of case head separation. That's the reason that I load the way I do. I haven't had a case head separation for the last 40 years since I changed my loading
procedures to reflect the needs of the rifle.
J E CUSTOM
Alex Wheeler
Well-Known Member
If you want to center a bullet in its freebore which has a clearance of .00025" per side then your necks must be fitted to the chamber tighter than that. Or the case body would have to be fitted tighter than that and neck sized with zero runout. Either way its not happening. What I am trying to say is for something to take control of centering the front of the round it has to have less clearance in the chamber than the bullet does. In Benchrest years ago they ran "fitted" necks. They fit the necks so tight they did not expand and could be reloaded without neck sizing. The idea was to center the bullet. Its no longer common practice because it does not produce better accuracy than a neck with generous clearance. Myself as well as others have tested neck clearance in 1k Br. They is no change in accuracy, unless you get too tight then things get worse. I have also test case/bullet runout on target at 1k.
I subscribe to the theory of not sizing the neck all the way to the shoulder. I leave 25% unsized to help center the bullet in the throat. Plus, FL sized and a .002 bump.
Alex Wheeler
Well-Known Member
Clearances. Look at a reamer print. The bullet has .00025" on each side of it (usually less) in a custom rifle. The bullet will allow .00025" of movement after that you have to start bending the case neck if the shoulder is going to do any centering.
Im just going to leave this alone. Im out.
bigedp51
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With a full length resized case the shoulder is the only part of the case that touches the chamber walls. The ejector pushes the case shoulder into contact with the chambers shoulder and has some centering effect.
The bullet centers the front of the cartridge in the throat and the recessed bolt face holds and centers the case in the rear. And this is what "the cartridge should fit the chamber like a rat turd in the violin case" means. Meaning the full length resized case gives the bullet "wiggle room" to be self aligning with the axis of the bore. Meaning the full length resizing and shoulder bump greatly reduces the chance of a warped banana shape case causing the bullet to be misaligned with the bore.
Also I would like to add that on a semi-auto the full length resized case should be .003 to .005 smaller in diameter than its fired diameter. This allows the case to "spring back" from the chamber walls and extract reliably. A semi-auto is not like a bolt action with primary extraction when the bolt is raised straight up that loosens the case grip on the chamber walls.
Kinda kills the partial neck sizing theory...
Not really. How much freebore do you have? .100", .200"? You think that is enough to completely locate a 3" long cartridge completely concentric to the bore? .00025" is quite a bit larger in the X axis 3" away. I could tell you exactly what that equates to but I'm not at my computer and dont feel like doing the math honestly.
