Measuring devices and issues with swaged bullets

[Cat Whisperer]

A few years back I picked up a jig to measure runout of bullets.  It had 2 double ended centers (into which one end of the bullet would fit inside) that were tapered inside to accomodate a variety of bullets.  In the middle off to one side was a dial indicator (.0001").

I've heard tell of bullet makers talk about watching the 1/10,000ths.

What are your experiences on relating the quality to accuracy?  In other words how good does it have to be to get consistancy or to squeeze the group down under 1/2 minute of angle?

[HWooldridge]

CW,

Articles I've read over the years indicate the the base of the bullet is the absolute and overriding important quality to accuracy.  I built my swage dies in a machine shop on modern equipment so there may be some runout but I can't detect any deterioration to performance.  IMHO, consistent bullet weight and bases will tighten groups more than runout of .0001 or more.

[Cat Whisperer]

HW -
  I whole heartedly agree with the flat base theory - it's one of those "thou shalt's".

  My question still stands, how important is variation in runout?  In terms of machining, should I hone (to make more round) after reaming (for size).  I probably will anyway for finish quality.  But with cast bullets - just because you're a .001 out of round with a cast bullet it doesn't make much difference as the bullet is so soft it conforms easily to the barrel.

But with copper jacketed bullets the resistance to being 'swaged' in going through the throat may affect chamber pressure - maybe not.  That is my curiosity.

[Donna]

Runout is not the amount of out-of-round a bullet is, it is the amount of how much the bullet is cocked or tilt it has in the case. This seems to have an effect on accuracy but I forgot what the articles said about it now, it has been many years. But it is on the order of a few 1/1000th of an inch or a few 0.001 of an inch. That is all I can say about it at this point. Let us know what you find out. :wink:

Donna

[HWooldridge]

CW,

Runout is the variation in the tip's alignment with true center.  In other words, chuck a loaded cartridge in a lathe and spin it against an indicator at the tip will measure runout but I think you are talking about an out of round condition in the bullet body.

I make finish cuts with a carbide-tipped boring bar using a light cut, plenty of oil and slow speed.  Without changing the setup, the hole should be as round as the lathe chuck's tolerances.  Although not likely, a reamer can be induced to cut out of round so I typically don't use them for fine work.  Some might disagree but I've had success doing it my way...HW

[talon]

The writings I've seen stated that polishing, and then hardening, the die cavity is mainly to ensure the walls are absolutely clean of tooling marks so that they don't hold the bullet from being easily pushed out by the punch. From experience I know this is much more important when working with annealed brass (or copper) jackets. Live brass jackets have springback and will most probably clear any minor wall imperfections, but those annealed ones really can hold tight if the walls are even slightly dirty let alone scored.  This has little if anything  to do with 'runout', but I believe your concern was to see what we had to say about the need to hone or polish the internal die wall when it is being manufactured  

[Cat Whisperer]

To me runout (per ANSI/ASME Standard Y14.5M 1994 and later) is any/all variation that can be measured by turning.  So it depends on what direction and the location of the dial indicator as to what's being measured.  It includes all sources, variation in surface, holding devices and bearings.  Therefore it is an incredibly usefull tool to use as it is easily done, but it's limitations are that it includes all sources of variation.

To specify something that runout esitimates, one could specify:
  roundness (circularity) where all points are equadistant about a point;
  cylindricity, where all points are equadistant about an axis; or
  perhaps coaxiality wherein the two axes in question coincide.

The problem of measuring those is that one has to make many measurements and calculations taking 30 to 40 minutes for each set done.  Obviously enough reason to use runout unless you're getting paid cost plus.

So the issue is in measuring runout two fold.  One the location and direction of the measurements and two, the devices (and the error introduced by them) used to hold the bullets.

This is why we have fixtures, with very precise bearings, for holding round elements for measuring - to avoid the error caused from the wear on the production equipment bearings.

One can devise all kinds of fixtures for measuring runout which can, if designed right, be indicative the bullet being out of round or when loaded whether or not it is reasonably aligned with the axis of the bore.  If the design is right it will have the same measurement as roundess or coaxiality PLUS the error of the bearings and fixturing.

[PaulS]

I can see that run-out can be in a bullet, case and loaded ammo. If there is run-out in each, it can multiply the over-all run-out or cancel it out. To me a bullet that has run-out is of more concern than case run-out because the bullet with run-out has little chance of being corrected once it is fired and will cause an out- of- balance condition that will adversely affect it's flight. If a cartridge fit a chamber well and the chamber has a neck and throat that fit close enough it can correct a bullet mis-alignment in the case to some degree, correcting the run-out problem so long as the bullet itself is true and symetrical along it's major axis.

PaulS

[Cat Whisperer]

Paul -

Agreed with the stackup.  

When I load, I neck size only 1/2 way down the neck.  That centers the case - wide at the base eliminating variation and wide at the neck with the sized portion holding the bullet centered in the chamber (with necks of the cartridge outside turned to increase coaxiality of the bullet to the bore).

In addition, by measuring each round in a jig, I sort on two criteria.  Those with bullet runout (putting the cartridge in vee blocks) with .001 or so are for match use; with .002 .003 or more for less rigorous applications.  I will also mark the high point of each loaded round and orient them all the same way - to decrease the group size by placing all the variation in the same direction.

That leaves the variation of the operator - the loose nut behind the rifle.

Dr. Mann in his book, The Bullet's Fllight, had much to say about the orientation (and orientation of defects) of the bullet and it's effect as it flew down range.  An oldie but a goodie.

[PaulS]

Cat-wisperer,
I tend to be anal about some aspects of shooting and not others. This is not to say that anyone else is, or is not, anal in aspects of their shooting, it is only to say this is the way that I see myself.

I neck size my cases to alloy about 1/8 inch of neck to fit the chamber and leave the body as it comes from the chamber as fired. I don't as a general rule check bullet or case run-out. I have in the past and even returned some bullets to Speer because they were out of round. My ammo is built for me to shoot at paper and game and all of the loads that I shoot are sub-MOA. (well the rifle rounds anyway) I don't index rounds because I load from a magazine (lazy).  I do segregate cases by weight, weigh each charge with stick powders, and double check each loaded cartridge. When I get a new weapon I spend the time to work up a load that is accurate in it - I have records of every load I have ever loaded for each weapon that I have owned or still do own.

So I do have my little "quirks" like everyone does.

PaulS