June 2, 2002, 12:00 AM | #1 | |
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Bullet Pull/Bullet Runout
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June 2, 2002, 12:19 AM | #2 |
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Rotational runout ?
I don't see a connection. Either bullet is straight and centered in the case or not......neck tension should have no bearing. I think. Sam |
June 2, 2002, 03:32 AM | #3 |
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First off - there's a couple (at least) types of runout = axial & linear (if you will). Axial is that variance of a spinning plate's "wobble" perpendicular to an axis. Linear would be more related to the "concentricity" of a bullet held in the brass neck.
Linear, for the sake of bullet-smithing (as axial really doesn't apply here) & concentricity is not the same as runout. Runout is the total indicated measure by your instruments relative to your baseline/datum (most likely your brass). We could further complicate it by doing the total runout versus the "regular" runout - one takes into account the entire surface under rotation versus only a specific axial diameter - it matters. Concentricity is the deviant of the two centers as averaged by your instruments & something not easily measured by common handloaders. Yes, it is different, subtley measured & does matter what you call it & how it is measured. Total linear runout should be considered for proper bullet alignment, throughout complete bullet length, which is usually called concentricity - except it isn't. Most all reloading "concentricity gages" merely measure one section/diameter of a bullet's linear runout as related to the brass & doesn't encompass the entire bullet length & still not fully capturing concentricity (which would more accurately be called total linear runout). To further exacerbate the measurement error, the brass itself is not in full compliance with the chamber (not an interference fit) so to not gain a complete understanding of chamber-to-bore/lands interface. Too, bore-to-chamber fit is likely not concentric, which obviates the whole discussion untill one has completely blueprinted the rifle. Confused yet? But, Sam did hit on it. The bullet should be straight in the brass' neck & aligned best you can with the bore. I don't see how neck tension, by & in itself matters as long as it is exactly the same. Ideally, the bullet should be held by neck tension just (& only) enough to preclude any deviance from perfect alignment. Of course, you need to start with that alignment to get there as an end result. Measuring it might be more trouble than it's worth. & arguing about the methods & definitions are right up there as well. Hope the answer was satisfactory & helpful. BTW, isn't the Lyman M die a flaring tool essentially for cast bullets? (this thread could go anywhere .... ) |
June 2, 2002, 10:51 AM | #4 |
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Grumble...
I just recently read an article by Mic McPherson on "Increasing accuracy by Increasing Bullet Pull" or something like that... Leaky old memory will not give up the magazine, probably Rifle/Handloader/TAR... If I find it, I'll post it later. I molyplate all my bullets, and have found that more bullet pull -- tighter bushing -- does improve my accuracy, for what that's worth. Agree with Sam: Straight is straight. Tom
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June 2, 2002, 02:20 PM | #5 |
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Perhaps...just perhaps...
That Lee is talking about their "factory crimp" die. This die crimps in 3 places around the bullet and it is suppose to replicate a factory crimp. Lets say that you crimp it too hard. Perhaps a hard pull forces the bullet out of round....sorta like a 3 jaw chuck on a lathe forcing a thin piece of pipe out of round. Now things are messed up. Your bullet is out of round, your neck is out of round and its possible that when chambering the round it could knock something out of alignment. This is not fact, it is just speculation on my part. I could be all wet. If so, I suspect I'll hear about it, but thats what make this place a great way to learn... |
June 2, 2002, 03:01 PM | #6 |
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Waste of time tryin to confuse me, I beat ya to it years ago.
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June 2, 2002, 03:59 PM | #7 |
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Concentricity is the deviant of the two centers as averaged by your instruments & something not easily measured by common handloaders.
Labgrade...correct me if Im wrong... Cant the concentricity of the bullet relative to the casing be established by resting the case upon 2 "v" blocks and the slowly spinning it be measured by a dial indicator ? What you call "axial" we call "perpendicular"...I think.... Also, if you are using a fired case specific to that rifle, it should take care of concentricity problem as the case is now the same size as the chamber. Thus your case should almost have an interfence fit on everything but the neck as it was only sized to hold the bullet. As for the chamber being lined up to the bore, there just aint much we can do about that except perhaps orient our cases exactly the same way each time. Maybe that works... |
June 3, 2002, 08:41 AM | #8 |
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I could not for the life of me remember the correct term for "linear" runout (in my last post - insomnia & the brain went first). The term is radial runout.
Watchman, it can, but you'd have to have dial indicators on the case as well to determine any of their radial runout simulaneously. Like I said, concentricity isn't an easy one to do with home-shop instruments. What you get when doing a "concentricity" check with V-blocks, is radial runout relative to the datum expressed by the outer profile/feature of the brass. Axial is perpendicular pretty much. Figure if you'd mount a shaft in a V-block rotate & measure the runout of a disc face perpendicular to the shaft - that's axial. Radila'd be measuring part of the shaft itself as it rotates, or anything in it same axis. A fired case will take on the shape of the chamber, which may (or not) be concentric itself). Too, the complete case has to (does) shrink somewhat or extraction would be way difficult. Every bit of the case (except head/web area) shrinks at the same relative rate. The reason we have to neck size is for proper bullet retention/neck tension. Agree though that measuring radial runout with standard reloading stuff will tell you amount of bullet wobble. Less is better ... |
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