Concentric bullet seating - tolerances?

Breach seated bullets probably enjoyed very good alignment. Bullets used there had quite
a bit of bearing surface, maybe 80% or more. Today in fixed ammunition, our bearin surface
is something just greater than a football, maybe 30-40%. Now clearly if you drop a .999 dia. pin
two inches long in a hole 1.000 dia and two inches deep you have great alignment. Shorten that
length to .045 or .050 and you have lots of room for error. That error could come to 10 degrees.
As pressure builds in a cartridge, does the bullet ease itself into better allignment, or does it slam
forward in its , as loaded attitude. Maybe its really a question of, does the neck give up its influence completelybefore the bullet moves, or after
 
If my rifle corrects to .0015, measured at some point on the bullet. Will not a bullet that is straighter than that be better aligned to the bore?

There is a chart in a book that was published by the NRA "Handloading" I believe, that shows the relationship between runout and accuracy. The article is on pages 86 and 87. I have no idea whether the data was simply calculated by an engineer, or was the result of actual tests. But if an engineer calculated it, that should be enough...right?
 
The discussion here is how bullet alignment with bore is determined not how good or bad it might be. The alignment depends on clearances and length between points of contact.

It's just a simple geometry problem. Exactly at what point this alignment is achieved is irrelevant except to note it happens just before the bullet starts down the bore and not back in the reloading process.

If you compare 2" long contact with .05" contact you will certainly get a wide spread in degree of alignment. This is unrealistic and tells you nothing. Use something like .2" compared to .15" and you will have a better idea of what really applies.

There's little doubt the bullet will change it's alignment as it goes from throat into the bore, No one can know if it gets better or worse but any reasonable analysis would lead one to believe it probably straightens the bullet up to where it is only slightly misaligned. No one knows also, how much of the group size is due to misalignment.
 
Pacecil,
If the chambering of a round can only straighten a bullet's alignment to a given point, and dies can achieve concentricity that is greater than that, then they rather than the chamber are the determining factor. I think that you have oversimplified the problem. Beyond the theoretical, how much hands on time (loading, in come cases straightening, chambering, and measuring) have you devoted to this little problem?
Goodgrouper,
I think that you should stop worrying about flags and tune and spend all of your bench time worrying about how straight your ammunition is. ;) One of the major advantages of bringing a concentriciy gauge to a match, and spending a lot of time intently fiddling with your ammunition, is that lots of other shooters are distracted by worrying about how their ammo will measure. We really don't spend enough time talking about mind games, in discussion of match strategy.:D
 
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I re-installed the kostyshn barrel on my VFS rifle last night and tested some new bullets today in it. That barrel is a very loose one until the last two inches at which point a patch becomes hard to be pushed through. Me thinks with a barrel of this configuration the last two inches will make up for any other ills in alignment either in the case or at release. This barrel might be an exageration of other more conventional bores but I think they react the same as this one.
 
To Boyd Allen....

I know only the big name shooters take a real hands-on shooting approach to these problems. Us "keyboard" shooters can just put forth the "theoretical" stuff!

I Ioad for everything from .17's to .45's including the BR calibers in between, and have been doing it for about 60 years. I have always had a problem with T I R in my loaded rounds. I feel good if I can keep it below .002 - most of the time it's around .003 - .004..... up around .005 - .007 I worry. I keep fooling with the dies and cases, but in spite of all I do it just seems impossible to consistently keep those little bullets straight in those cases. And for that matter it's hard to keep the necks straight.

However.... I've checked rounds with high runout and have never been able to measure a difference in group size that I could absolutely say was caused by runout. In addition.... I can't see anything in the "theory" that would indicate bullet runout would cause the bullet to misalign in the throat. Finally....a whole bunch of really good shooters say they can't see that runout enlarges their groups.

After all this, you know what? I still want to keep runout down as low as I can in my loaded rounds.
 
Pacecil,
Making straight ammo,is all about getting 3 points to land on the same straight line.
This is really a simple principle. Since we need some clearance in our seating dies to
allow assembly, zero runout is not practical, though it would be nice. Sizing necks
giving runout in .0001-.0002 is not complicated either, But you already know this
Runout in the area of .003-.004 and occassionally more, says somethng
is out of allignment
 
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Pacecil,
At the risk of being accused of adding to the supply of anecdotal somethingortheother (Actually, I forget...oblique reference to another thread.) Let me relate a story.

My first quasi bench rifle was a 722 that was in an old single shot 40x rimfire stock, that had had the bedding device cut off and the accessory rail slot filled in. It had a HV contour Hart barrel that started out 24" long. The chamber had a .244 neck, and it liked 53 gr Sierras, 205s, and, of all things,748. The chamber was designed around a one piece FL die, but most of the time I used custom fitted Wilson dies. I loaded at the range, Shot off a home made front rest, and used 6' 1x2s with surveyor's tape to try to read the wind. It was a steady performer in the area of 1/4 - 5/16 at 100 yd.

One afternoon, with mild temperatures and wind, I was shooting groups that were all touching and all of a sudden I had paper between. Surprised, i started looking for an explanation. Coindidentally I happeded to have taken a concentricity gauge (given to me by a friend) with me that day. Being familiar with the usual reading, I was surprised to find that the last few rounds from the small batch that I had just loaded were not to the usual standard. I figured that something was wrong with one of my dies. Upon inspection I found a particle of ball powder stuck to the inside of the seater, about half way down the body cavity. I removed it; the rounds went back to their previous readings, and all of the shots went back to touching. That was good enough for me. Now ask me if I can tell the difference between the 6PPC rounds that are .0015 or less out of my seater, and those that I have straightened to half of that......Heck if I know, but straighter makes me more confident, and confidence counts.

Once, when I took a new gauge to a match and was busily straightening as I loaded, I had several friends come other to check their ammo, and one fellow repeatedly exclaim that he didn't care what his measured, and wasn't going to check them. (Methinks he doth protest too much...(Wlm. who?))

Now about that runout...for factory chambers and unturned necks I have heard reports, and personally found that if you neck size with a Collet die and then use a body die with a slight bump, you will get the most consistently straight ammunition (measured on the bullet). Try it, you might like it, and do it in that order; it matters.

I have worked a lot on this problem, both for factory and a competition rifle. If money were no object, i would order a set of FL reamers, matching my chamber reamer, with a selection of neck diameters, and stick with one piece dies. These have given me the most consistently small runout. Whether the difference matters is another matter. Below a certain point, I don't know.

BTW I appreciate you telling us about your shooting history. Many of your posts have seemed to be about theory, so I didn't have a way to judge your "on the ground" experience, which, as you have explained, is considerable.
 
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Maybe a Pressure Ring Problem?

Have you checked the pressure ring on the bullet? A soft case neck and a good pressure ring will cause the bullet to "flop" around in the neck when you seat and the ring expands the neck more than it will spring back. If this is the case no amount of jamming into the lands will straighten your bullet, so I have discovered.
 
Have you tried shooting the non-concentric rounds? Straighten a half dozen to your desired runout and load a half dozen and dont check them for runout. Go to the range and shoot a few groups in good conditions. Thats the kind of knowledge that you can learn the most from. Straighten them if they shoot better, if the straightened rounds shoot worse or the same, sell your concentricity gauge and buy more bullets to shoot. And seating depth is a funny one, a critical measurement to some that load for a weekend shoot, bounce them down the roads of America to the range far away and shoot them without running them through the seater again. This works for alot of shooters, good shooters. Doesnt work for some. Find out what works for you and roll with it. Dont worry about things that have little or no effect. By the way, One over looked runout cause ,,, sharp or poorly tapered case mouth shaving a small amount of the pressure ring during seating can be a likely cause. was for me ..
Andy B
 
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