Upon ignition, does the bullet leave the case first, or does the case seal the chamber first?

Good question Ralph!!!!!!!!!!
Would like to here from a lab on this but, I would think that if the bullet is crimped the seal would come first. If no crimp I would think that almost simultanously (sp?) with the resistance as the bullet hit the lands which would also, for most chambers, before the bullet acctually exits the case.
Although, under that much sudden pressure is there enough neck tension to hold the bullet while the soft walls of the case expand to seal?

If it is not apparent, I am just guessing!!!

Smedley

Because here lies the problem with runout:

If the case seals first, then it will induce runout, and render my efforts to minimize runout useless

But looking at my case necks, I see powder fouling. The higher the pressure, the less fouling and it stops higher up on the neck. This implies that the bullet is out of the neck before the brass seals the chamber.

When the firing pin hits the case, the case is shoved forward until it contacts the forward end of the chamber, at which time the firing pin continues forward and ignites the primer. The expanding gases push the case back against the case head, taking up the extra length in the chamber that originally allowed the case to be chambered. The case expands laterally until there is no room for expansion left, at which time the gas from the continuing propellant burn begins to expel the bullet from the case.

quote:

Originally posted by Doubless:
The expanding gases push the case back against the case head [you mean bolt face?], taking up the extra length in the chamber that originally allowed the case to be chambered.

What are the gasses pushing against on the opposite end?

I am no engineer, but in my way of reasoning I would expect that the bullet is pushed out of the case into the lands where there is a sudden resistence that slows the bullet down.

At this instance, the gases are slammed against the bullet and begin to divert to the edge of the case mouth where there's less resistence.

The force of the gases crowding at the back of the bullet causes the case mouth to expand to the chamber walls, thus forming a seal. As soon as the case mouth creates its seal, the bullet gets a push from the compressed gases and everybody in the chamber starts their journey toward the muzzle.

That is an awful lot of stuff to happen in a very short period of time.....

So the bullet is first jammed into the lands, then the case is pushed back against the bolt face, as the case walls continue to expand to seal the chamber?

.

You da man, ALF!

Where did you obtain this precious intelligence?

quote:

Originally posted by Doubless:
The expanding gases push the case back against the case head [you mean bolt face?], taking up the extra length in the chamber that originally allowed the case to be chambered.


What are the gasses pushing against on the opposite end?

My reply is probably moot, but yes, I meant bolt face, and the gases are pushing on the inside of the case, at the web. That is where the ~.005" of difference comes from between a new factory (or full length re-sized) case and a fired case. It is case stretch, caused by gas expansion before the bullet ever moves.

.

quote:

Originally posted by Ralph Hyrlik:
Because here lies the problem with runout:

If the case seals first, then it will induce runout, and render my efforts to minimize runout useless ...

Hey Ralph, Have you ever tried Partial-Full Length Resizing(P-FLR)?

The reason I ask is because most people concerned with Run-Out seem to be Neck Sizing their cases.

I P-FLR and never give Run-Out a thought.

When you do a partial full length do you follow up with a neck sizer or settle for a partial neck resize?

I neck size, but bump the shoulder back with a Redding Body Die. Whatever runout I get I can fix with my Bersin tool, but I was thinking that all my efforts would be countered by the brass being reformed during ignition. Now, I feel better.

Ralph-If you are neck sizing in your primary operation and then bumping the shoulder back in a full-length die (which you referred to as a "body die"), you are NOT neck sizing and in fact are being quite counterproductive.

You are full-length sizing.

You can't bump the shoulder in a FL die without fully sizing the case unless you have a die made up with custom dimensions.

Also, soot on cases is common in low-pressure loads or on heavy-necked brass (such as 5.6x57 rimmed) right up to the point of reaching max pressures. It is really nothing to worry about as accuracy can be exceptional at lower pressures as well as with full-throttle loads.

The Redding Body Die does not size the neck, just the body and not as much as their FL die does. I don't have any issues with runout anymore. My question concerned what happens to runout upon ignition.

Ralph-I was just trying to save you some effort. The body die combined with the neck sizing still equals full length sizing and an additional step that can be eliminated. Even though the Redding die may not size it as far down as a true FL setup, it still reduces the diameter somewhat.

Just a question.......

How does the cases position at the bottom of the chamber relate to the runout we are trying to avoid? The case must be to some degree smaller then the chamber, and gravity will cause it to lay on the lowest point in the chamber. The bullet must then enter the throat at a angle of some sort when leaving the case unless the case has fully expanded and centered itself in the chamber first.
Maybe all this effort to eliminate runout is for naught??

quote:

Originally posted by Dwight:
When you do a partial full length do you follow up with a neck sizer or settle for a partial neck resize?

Hey Dwight, I agree with Bobby, when you P-FLR, the entire Caseneck is resized. So you do not need to use a Neck Sizer then.

quote:

Originally posted by Ol` Joe:
...How does the cases position at the bottom of the chamber relate to the runout we are trying to avoid? The case must be to some degree smaller then the chamber, and gravity will cause it to lay on the lowest point in the chamber. The bullet must then enter the throat at a angle of some sort when leaving the case unless the case has fully expanded and centered itself in the chamber first.
Maybe all this effort to eliminate runout is for naught??

Hey Ol` Joe, That is right on the nose for a Controlled Feed rifle with a Fixed Ejector. If the rifle has a Spring type Ejector, then that pushes the Case to the Chamber wall, opposite the Ejector.

With a proper P-FLR that has a slight Interferance Fit(aka Crush Fit which equals Zero Headspace), a Bottleneck shaped Case is held in Compression between the Boltface and Chamber shoulder. That "forces" the CenterLine of the Case to be closer to the CenterLine of the Bore and results in slightly better accuracy for me.

The really nice thing about P-FLR vs. Neck Sizing is that anyone can prove it to themselves by simply running a Blind Test. Make some up both ways and have a buddy hand them to you without telling you which type is which. Then see what the Targets tell you.

That said, for the folks that still prefer Neck Sizing, I'm all for them. People should use the Method that they like the most.

quote:

Originally posted by Bobby Tomek:
Ralph-I was just trying to save you some effort. The body die combined with the neck sizing still equals full length sizing and an additional step that can be eliminated. Even though the Redding die may not size it as far down as a true FL setup, it still reduces the diameter somewhat.

I disagree.

I found that if I size in three steps, I maintain .001"-.002" runout. If I size in one step, some cases are .001" and some are .006". This was with the same batch of Norma brass.

My finding is that the less brass you move, the more concentric the case remains. I Body size first. No change in concentricity. I then neck-size and decap with a bushing .003" smaller than the fired case. Concentricity does not change. I then finish with a .006" undersized bushing. Concentricity may change by .001", but not any more than that.

quote:

Originally posted by Ol` Joe:
Just a question.......

How does the cases position at the bottom of the chamber relate to the runout we are trying to avoid? The case must be to some degree smaller then the chamber, and gravity will cause it to lay on the lowest point in the chamber. The bullet must then enter the throat at a angle of some sort when leaving the case unless the case has fully expanded and centered itself in the chamber first.
Maybe all this effort to eliminate runout is for naught??

True, but if you have .007" runout, and .002" airspace between the chamber wall and the case wall, the bullet may be badly mangled by the throat as it leaves the case neck.
If you seat into the lands, the bullet will be mangled during chambering.

Ralph Hyrlik wrote: "If I size in one step, some cases are .001" and some are .006"


If that's the case (pardon the pun), you have other issues to deal with. That much discrepancy is not the norm if you are maintaining consistency in your techniques.

If that was the case, then I would have the same results in my multi-step process.

There is nothing wrong in my technique. Same press, same die adjustment.

quote:

Originally posted by Ralph Hyrlik:
Upon ignition, does the bullet leave the case first, or does the case seal the chamber first?

Probably depends on which cartridge you're talking about and the load being used. Since a high-powered rifle cartridge develops its highest pressure after the bullet is at least 4" down the bore, it is likely that the cartridge case doesn't expand enough to seal the breech while the bullet is still in the case.

Speaking of technique,

Partial FL sizing sizes only half the neck, no?

quote:

Originally posted by Ralph Hyrlik:
Speaking of technique,

Partial FL sizing sizes only half the neck, no?

Hey Ralph, No, that would be Partial-Neck Sizing. And nit picking a bit, it can be done with a Neck Sizing Die all the time. Or if the Die and Chamber dimensions are compatable it can be done with a Full Length Die.

I'm not on a crusade to get you to quit Neck Sizing, because if you are happy with it, I'm all for it. If you want to try Partial-Full Length Resizing(P-FLR) you will need a Full Length Die.

Maybe this will help a bit:

Here we go for the vast majority of Die Sets. This does not include the Lee Swaging/Crimping Die Sets which are unique unto themselves:

Full Length Resizing (FLR)
1. Reforms a Case to fit within any Chamber that meets SAAMI Specifications.
2. It has some unknown amount of Headspace.
3. The CenterLine of the Case and the CenterLine of the chamber are not in alignment. On Fixed Ejector rifles, the Case lays on the bottom of the Chamber. On Spring Ejector rifles, the Case is skewed to the opposite side of the Chamber from where the Ejector is pushing against the Case Head.
4. You set the FL Die by screwing it in until it touches the Shell Holder on a raised Ram, lower the Ram, screw the FL Die in an additional 1/4 turn and set the FL Die Lock Ring.
5. You have short Case Life due to Incipient Case Head Separations.
6. Accuracy is generally acceptable to fine.
7. You only need a Full Length Resizing Die Set.
8. Intended for use in Dangerous Game Rifles, semi-autos, pumps and most single shots.
9. You must Lube the cases and then remove it.
10. No need to ever Re-adjust the Fl Die Setting for use in any rifle of the same caliber.

Partial-Full Length Resizing (P-FLR)
1. Custom fits a Case to a specific Chamber.
2. It has a slight "crush fit" to eliminate all Headspace.
3. The CenterLine of the Case and the CenterLine of the Chamber are forced to be in perfect alignment. The Case is held in Tension between the Bolt Face and Chamber Shoulder, regardless of the Ejector type.
4. You set the FL Die by screwing it in until it is about the thickness of a Nickel above the Shell Holder on a raised Ram. You Lube and Resize a Case, remove the Lube and try it in the Chamber. Lower the FL Die 1/8th turn or so and repeat the process. You might reach a point where you CAN NOT close the Bolt or where it is very difficult to close. Screw the FL Die in 1/16th turn and repeat until the Bolt closes with "snug" resistance. If you go too far, back the FL Die up 1/8th turn and try again on a different Case.
5. You have the longest possible Case Life due to Zero Headspace.
6. Accuracy is generally fine to excellent.
7. You only need a Full Length Resizing Die Set.
8. Intended for use in Bolt Action Rifles and some single shots.
9. You must Lube the cases and then remove it.
10. You may need to Fine Tune the FL Die adjustment the first couple of Reloads.

Partial-Neck Sizing (with a FL Die) (P-NS w/FL)
1. May or may not reform part of the Case Body depending on how closely the FL Die dimensions match-up with the Chamber dimensions and is best used in one specific Chamber.
2. It has some unknown amount of Headspace which varies with each shot until the Bolt will no longer close and then the Shoulder must be “Bumped Backâ€.
3. The CenterLine of the Case and the CenterLine of the chamber are not in alignment, but become closer with each shot until the Bolt will no longer close. On Fixed Ejector rifles, the Case lays on the bottom of the Chamber. On Spring Ejector rifles, the Case is skewed to the opposite side of the Chamber from where the Ejector is pushing against the Case Head.
4. You set the FL Die by screwing it in until it Resizes approximately 1/2 of the Case Neck or less.
5. You have shorter Case Life than P-FLR, but longer than FLR.
6. Accuracy is generally fine to very good.
7. You only need a Full Length Resizing Die Set.
8. Intended for use in Bolt Action Rifles.
9. You may or may not need to Lube the cases and then remove it.
10. You may need to Fine Tune the FL Die adjustment the first couple of Reloads.

Neck Sizing (NS)
1. Only reforms the Case Neck and is best used in one specific Chamber.
2. It has some unknown amount of Headspace which varies with each shot until the Bolt will no longer close and then the Shoulder must be “Bumped Backâ€.
3. The CenterLine of the Case and the CenterLine of the chamber are not in alignment, but become closer with each shot until the Bolt will no longer close. On Fixed Ejector rifles, the Case lays on the bottom of the Chamber. On Spring Ejector rifles, the Case is skewed to the opposite side of the Chamber from where the Ejector is pushing against the Case Head.
4. You set the Neck Sizing Die by screwing it in until it Resizes any amount of the Case Neck you desire.
5. You have shorter Case Life than P-FLR, but longer than FLR.
6. Accuracy is generally fine and gets better with each shot "until" the Case Shoulder needs to be "Bumped Back" slightly.
7. You need a Neck Sizing Die and will eventually need a Full Length Resizing Die unless you trash the Cases once they need the Case Shoulder moved back.
8. Intended for use in Bolt Action Rifles.
9. No need to Lube the cases.
10. No need to ever Re-adjust the NS Die Setting.

Hot Core,
Thanks for that lengthy but clear description. I do a P-FL but I set my die a little closer to the ram than you describe for hunting purposes. It is a good habit to check all the loaded rounds for fit prior to a hunting trip.

I fully agree that partial neck sizing works wonders, but it is not an option on a WSM hunting rifle. There the whole neck needs to be sized, and therein lies the problem. The only way to get a straight neck from a factory chamber is to size it a little at a time.

quote:

Originally posted by Dwight:
Hot Core,
Thanks for that lengthy but clear description. I do a P-FL but I set my die a little closer to the ram than you describe for hunting purposes. It is a good habit to check all the loaded rounds for fit prior to a hunting trip.

Hey Dwight, You are welcome. I do agree that in order for P-FLR to work properly, the adjustment is slightly different for each rifle and set of Dies. It does make it real nice that we can "adjust" the set-up for a Custom Fit.

quote:

Originally posted by Ralph Hyrlik:
I fully agree that partial neck sizing works wonders, but it is not an option on a WSM hunting rifle. There the whole neck needs to be sized, and therein lies the problem. The only way to get a straight neck from a factory chamber is to size it a little at a time.

Hey Ralph, Any idea why you are noticing that being different for the WSMs than other cartridges?

Because they don't feed as smoothly from the magazine, and sizing half the neck does not provide adequate tension.

Hey Ralph, Interesting observation. Thank you.