Loaded round concentricity !!

B

Bryce

Guest
Just another thread about something other than tuners and personal issues ! Lets push those ones down the board and over to page 2 to be forgotten !!

I have a little test that I am going to run this weekend if the weather is kind enough.

I have some ammo preloaded with 30.1 grains N133 and a 68 Ultra jammed hard. This load has been shooting well lately and with the late Autumn conditions here at present should work well again, all things being equal.

I ran all my ammo over a concentricity gauge, nothing fancy just a RCBS one set up so that the tip of the dial indicator sits just below the case shoulder with the round supported on the blocks at the rear of the case and out near the tip of the bullet. The spring pressure from the indicator holds the round in place and it is easy to get accurate readings.

Most of the rounds ran pretty good but I gave some a little nudge from my thumb to tweak them straight so that they have less than 1 thou TIR.

I also took some ammo and gently bent the bullet over in the neck with my fingers so that they have 5 - 7 thou runout.

Any predictions as to whether those with the very obvious runout will shoot notably worse ? How much worse ? I have a hunch that they will be damn close to the straight ammo groups.

I'll get back here with what I find.

Anybody else done this test ? Any dramatic reduction in accuracy ??

Bryce
 
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Bryce, I would bet that the rounds that have .005-.007" run out will shoot very close to those with .001-.002" runout...I believe the chamber if tight neck will remove most of the miss-alignment...I hope..:D
 
Id guess that jammed hard the loads .005-.007 out might straighten themselves out somewhat when chambered.
 
Guys,

I must admit I was surprised how easy it was to straighten the slight runout to have pretty much none. It did however take a decent but if finger power to bend straight rounds to have 5 thou plus, the thick necks for a 0.269 chamber and all. I can easily see maybe 2 - 3 thou being kinked straight in the chamber but 5 - 7 thou I am not so sure. :)

Will be interesting to see just how much this matters.

5 thou is a BUNCH of crooked ! I rolled them on the loading bench and the bullets are flapping up and down like flappy thing on a windy day !!

Bryce
 
Did It A While Back

When I first got that little Bruno Checker, I sat down with my Rail Gun on a good day and tried,as best I could, to ascertain just how much runnout is "too much".
My dies will typically produce rounds that are .002 or less. I delibertly shot rounds that exibited .004 runnout into a group, and for all general purposes, they went in.
I did what you plan on doing, tapped a few around to where they showed .005 runnout or worse. That seemed to be about the break point,as it was very difficult to shoot sub .200 groups.
But then, I repeated the same test, shot another five shot group with some rounds running "zero', and some running .005. That group was about .100 flat. Go figure.
I honestly cannot say one way or another what is "too much" runnout. Unless you are in a tunnel, in a perfectly controled atmosphere, it is darned difficult to get any results that you can take to the bank. Truthfully speaking Tomball is not the ideal place to attempt things such as this.
But, since we take all the pains that we do in chambering to "tenths", turn necks to exact standards, demand bullets that are "zero", demand that our actions be dead on true, then it would only make since to load rounds that reflect this same committment to accuracy.
The whole idea is to arrive at a round that, when chambered, has the bullet as close to "zero" alignment to the bore as possible. If the chamber is crooked, it won't be. If the action is not truly straight, it won't be. If the necks are not consistant in wall thickness, it won't be.
I guess it is the old, "a chain is only as strong as the weakest link" thing. It makes no difference where the culprit lies if the result is that a bullet that is not in dead true alignment when chambered. Saying, "I can chamber a barrel to within .0001" doesn't make much sense if you then cram rounds into it that exibit .005+ runnout.
There is a pretty good number of shooters who believe all of this is just a bunch of hype. If you have a great barrel, great bullets,and know how to arrive at a great tune, than all of this other "stuff" just doesn't make much difference. I sort of bounce from one crowd to the other, depending on how "anal" I feel at the moment. The truth be known, there are times when I can sit down with my Rail Gun and absolutly amaze myself in how easilly I can shoot small groups. Then, there are other times when I feel like my entire program is demon possessed.
But, we keep trying........jackie
 
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Thanks for the input Jackie.

I totally follow your logic on this. My set up usually produces around 1 thou runout with the ocassional round up near 2 thou. If I can shoot good groups with more than twice the runout my set up prduces then I figure I can retire the concentricty gauge !! :)

I'll post back when I have shot the wobbly rounds, I swear you can see the crooked just holding the rounds between thumb and finger and spinning them !!

Bryce
 
Francis,

I first set the gauge up to read on the back end of the neck on a sized case, then at the front edge of the neck where it has been sized and then out on the bullet about 3/16 above the neck and again out near the tip.

Finally I set up so that the rear of the case and near the tip of the bullet were supporting the round and the reading being taken more or less mid way just below the shoulder.

What I found was the cases were straight as best I could tell and only when I got well out on the bullet did I get readings that were getting up above 2 thou maximum on the ocassional round.

Reading below the shoulder were less than out near the tip just due to the geometry but where a lot easier to read accurately so were chosen as the best method for comparison purposes.

In every case the rounds showing the worst run out were always the same rounds regardless of how they were measured and the best were always the best. It seems that the cases are so close to perfectly straight that it doesn't matter and the run out is all in the sized part of the neck and maybe the seating.

I previously seated some rounds with a PPC-USA Redding competition die (so the round was a bit sloppy in their) and they only gauged slightly worse than those seated with a custom chambered Wilson seater.

Gee it's nice talking benchrest stuff !!

Bryce
 
Bryce,
My set up is very similiar, Bullet supported in a center drilled
hole at a point .060 back from tip. Rear of case sets on 2 ball
bearings and dial ind. .0001 just in front of case mouth. I have
a 40tpi. screw centered over neck that allows me to straighten
and I do . I straighten to about .0005 TIR.
Above .0025 in ideal conditions I can see a difference, though not
much. Many dies will load an occasional round above .004 and
they will go out. I must say that I believe some bullet are more tolerant
than others. I think the ultra may be one of them. Those with a true
cylindrical body may be the worst. try jumping bullets that are loaded
crooked and you will have an eye opener.
I'm presently working on a champhering tool that cuts a pecise
angle at any given depth that it is set for and it helps the TIR
a little more. We really have no way of keeping that chamfer
straight. File a case mouth crooked and then seat a bullet. The
mouth of the case is really much like a crown as the bullet leaves it.
Experiments are fun !!
 
My loaded rounds typically have about 0.0015 to 0.0020 runout. It bothered me until one day I chambered a typical loaded round with a fair amount of jam. Then removed that round and checked the runout. It was less than 0.0005. Apparently the bullet was centered when I chambered that round. Try it yourself and see what results you get.....you might just be suprised........Donald
 
Donald ...

Donald said:
My loaded rounds typically have about 0.0015 to 0.0020 runout. It bothered me until one day I chambered a typical loaded round with a fair amount of jam. Then removed that round and checked the runout. It was less than 0.0005. Apparently the bullet was centered when I chambered that round. Try it yourself and see what results you get.....you might just be suprised........Donald
Click to expand...
Interesting. How much neck tension did you have on the bullet ??? How much jam did you use ??? Art
 
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