Reloading: Measuring Bullets

A couple of recent letters, including this one from Richard prompted me to give some thought to bullet measuring.  I hope this article covers the topic effectively enough to make you do some thinking as well.  - GAS -


Measuring Bullets
by Germán A. Salazar

Germán:

I recently received a box of 80 gr. VLD Berger bullets and took measurements of four bullets.

From base to tip 3 measured 1.0985" and 1 measured 1.015".

From base to ogive they measured .4970", .4975", .4985" & .4990". This variance is what you previously said I could expect.

Next I used the Stoney Point LNL (with the metal rail not the plastic they furnish now). I figured I made a mistake with the results I got, so I did each one over three times but all four bullets measured the same from the base to the ogive at 1.848". I then checked from the base to the bullet tip and all four measured the same: 2.438".

STRANGE

So, if I seat 10 thousands (0.010") into the lands, I should be safe - I hope - as I never seem to get the same seating depth no matter what I try. I probably will first try seating at the lands.

I must be doing something wrong with the seating die. I've thought of going to the Wilson seater with the arbor press but I'm not sure if this will correct whatever I'm doing wrong.

It's really frustrating when one bullet is 1.848" depth, the next is 1.846" and the next is 1.847".

I also measured four 90 gr. Berger VLD's and have to do it over as the measurements are all over the place. Time to stop as I'm getting tired. Continuing is a bad idea.

Have not had the chance to fire a box of Remington to break in the barrel and then do a check with a fired round using the Sinclair Seating Depth Gauge.

Richard


Richard,

Your experience and questions bring up several points worthy of discussion.  I'll break them down into a few basic questions and give you my thoughts on them.

1.  What am I trying to accomplish?
2.  Will measuring bullets help me to reach my goal?
3.  If I choose to measure them, what should I be measuring?
4.  What are the problems and sources of error in measuring bullets?

1.  What am I trying to accomplish?
As always, I begin from the premise that we're strictly speaking about Highpower shooting, not any other discipline.  With that in mind, I believe that what were trying to accomplish is to load ammunition with a high (but not necessarily extreme) level of accuracy, in moderate volume, to be fired under a variety of conditions on a target with relatively generous scoring rings (our 2 moa 10 ring).  Accordingly, I tend to select high quality components (like Berger bullets) and do very little checking.  Over the years, I've found that this approach lets me use my limited reloading time to best effect, but it certainly isn't the only approach to high accuracy. 

The ultimate goal of any reloading process should be to create uniform and accurate ammunition.  Any measuring process is more geared towards uniformity than accuracy which is best handled through component selection, powder charge and other similar factors.  Uniformity of bullets, however, should lead to uniform seating depth which is certainly an element of an accurate load and a worthwhile goal.  So uniformity of seating depth is our objective.

2.  Will measuring bullets help me to reach my goal?
Maybe...  If the bullets you've selected have a significant degree of length variance (we'll discuss the critical dimension further down) then perhaps sorting would help.  However, I tend to think that if a bullet has significant length variance, that perhaps the quality of manufacturing isn't really up to my needs and I'd be better off with a different make of bullet.  For the record, I use Sierra, Lapua, Berger and Clinch River bullets with no reservations.

If the bullets has only a small amount of length variance, then I don't believe that measuring and sorting them will materially aid accuracy in a Highpower match.  Depending on the bullet, I will seat them in the case so that they are jumping to the rifling, or (more frequently) so they are jammed into the rifling.  In either circumstance, the amount of jump or jam is never less than 0.010" and usually 0.020"; that's enough to account for small variances in length.  The worst possible seating depth is right on the lands; at that point, any small variance will have some bullets jumping, some jammed and a few right on the lands; this will result in significant elevation dispersion.  By jumping or jamming a reasonable amount as described above, you ensure that all of your bullets are doing the same thing.  Small differences in the amount of jump or jam are far less significant that jumping some and jamming others!

3.  If I choose to measure them, what should I be measuring?
I know my process is not universal and some people will want to measure their bullets - maybe just because they can, maybe because it gives them confidence or maybe because their curiosity is insatiable.  That's fine, let's see what might be useful to measure in order to achieve our goal of uniform seating depth and well examine the principal problem that stands in your way.

First let's consider where the bullet contacts the rifling and how the seating die contacts the bullet.  The bullet, of course, contacts the rifling along the length of its full-diameter shank, beginning at the end of the ogive, where the curvature of the tangent or secant ogive shape flattens out.  There are plenty of tools that will indicate this location pretty closely, I use the Sinclair hex nut comparator for this task.  Although the inside diameter of the .30 hole isn't quite .308" (if it were, the bullet would slide through) it is close enough and in any event it provides a consistent point of reference. 

In this picture you see a bullet inserted into the Sinclair hex nut comparator and I've made a red mark on the bullet so that we can see just where the full diameter shank begins.  As I hope the picture shows clearly, the shank begins at the top of the red mark where it is against the hex nut.  The top of that red line is our first critical point, let's call it the shank line.




Next let's slide a case and the bullet into the seating die.  Here we're using an old Vickerman seating die because its cutaway front exposes the seating stem which contacts the bullet and is really the focus of our attention.  As you'll see, the stem contacts the bullet well above the shank line - that is precisely the source of most problems in bullet measuring.  If the stem contacts the tip of the bullet, the situation will be especially bad because the tips on hollow-point match bullets are somewhat irregular.  However, most match-grade dies have a deep enough cavity in the seating stem to avoid that further problem.

What are the problems and sources of error in measuring bullets?

Next let's make a blue mark on the bullet right where it contacts the seating stem.  let's call this point the stem line.  Obviously, making these marks with a marker leaves a bit of a smudge, but since I'm doing this just to illustrate a few concepts, it's of no great consequence.

Now here's the bullet with both marks.  I have the calipers open to show the distance between the shank line and the stem line, but there is no way to precisely measure this distance and no matter how precisely you scribe those lines, the actual measurement will be imprecise enough to make it a futile effort.  Unfortunately, this is the single most critical distance in a bullet as it will determine the uniformity of jump or jam to the rifling on the loaded cartridge.  It is the variance in this distance that we should be trying to measure, but I don't know of any way to do that with a useful degree of precision.  That's why I don't measure bullets.

Here's a frequently taken measurement: base to ogive line.  I don't see any value to this measurement because we really don't deal with the base as an element of seating the bullet and this distance is really not relevant to our goal of uniform jump or jam.  Imagine measuring a set of bullets made in two bullet-making dies which happened to make this dimension identically but had a 0.030" difference in the shank line to stem line dimension described above.  Did you measure the right thing?  Would it help reach the goal?  No.

Here's another frequently taken measurement.  Other than being easy to measure, I can't see that there is any reason at all for checking the overall length of a box of bullets.  The tips, and therefore the overall length, vary enough to give anyone heartburn.  But the tip is irrelevant to the seating process and thus its irregularity can be ignored.  Notice that the two lines in which we're most interested aren't being used at all in this measurement.  This measurement is a complete waste of time.

The case base to shank line measurement is ultimately what we're truly interested in.  This is the measure of jump or jam.  When you take this measurement and find variance, it is exclusively the result of variance in the unmeasurable shank line to stem line dimension.  If you were really dedicated (or simply nuts) you could seat all of your bullets about 0.010" longer than your desired dimension, measure each one and reseat it with an individualized setting on the die.  My eyes are glazing over just thinking about that process.  The simpler approach is to seat them to a reasonable level of jump or jam.  If some of my bullets are jammed 0.012" and some are 0.017" and a bunch are somewhere in between, I won't worry about it one tiny bit - they will all shoot to X ring elevation and that's my goal.

 

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