Precision Hand Loading For Long Range-Chapter Two: Bullet Prep
Now for another abbreviated test. This is probably only worthwhile if you have a very fine set of mechanical balance type scales or digital scales. Let’s weight 25 or so and make sure the weight is running pretty much spot on. I have never had much of an issue with weight variation in bullets coming out of a Yellow or Green box though I will say on semi-frequent occasion you will get a few nonconformists when working through a box. So as long as a small test batch looks good, we’ll assume the lot is fine unless you deem your time, and rifle’s potential worth splitting hairs. If so, weigh EVERY bullet and sort them in .2 grain (or finer) lots
Now we move to a critical test. We’re going to measure the length of the bearing surface of the bullet. Evidently this spec is far harder for the manufacturers to hold than weight or diameter. The bearing surface is the only part of the bullet that touches the bore/rifling. Let say we have a standard bearing surface length of (.500”) a half inch for the sake of round numbers. Great. But if a bullet shows up with .490” bearing surface, which is .010” (10 thousandths) short of standard, we know it will not have as much surface rubbing the bore, which will not cause as much pressure buildup, so that bullet will achieve a lower muzzle velocity and it will impact low. Ah ha! Now we are learning.
And the same can be said if a bullet shows up with a .510 bearing surface or +.010” longer than standard. We know it has a little more surface area contacting our bore, which equates to more resistance, which equates higher pressure and more velocity. Yep, you guessed it. This bullet will achieve higher MV and it will impact high. So let’s make a pact we are going to sort our bullets into groups of bearing surface lengths so that when we shoot long range we are all smiles, deal?
How do we measure bearing surface lengths? Glad you asked! There are several ways, but since we most likely already have a set of dial/digital calipers, let’s just got that route. It’s a little cheaper too. Hopefully by now you have received in the mail your bump gauge attachment for your calipers that we spoke of in Chapter One: Brass Prep. But let’s revisit the tool because we’re gonna need an additional one as well as two inserts.
You’ll need two of these to measure the bearing surface of your bullet. (or one if you already have one for measuring you case headspace/bump length as spoke of in Chapter One: Case Prep.
And you’ll need two of these. They are bullet caliber/diameter specific!
So to measure the length of the bearing surface, we insert the bullet comparator inserts into the bodies and just slightly snug the set screw. Now place a body onto each jaw of the calipers and snug the thumbscrew. Make sure the comparator inserts are lined up with each other as closely as you possibly can. Do this by feel, dragging a finger across from the end of one to the start of the other where they meet.
Now with the comparators gently slid together zero your calipers. Take a couple of dozen or so bullets and measure the bearing length. Write down the most consistent reading of the bunch and call this the measurement “they are supposed to be.” I get several containers and place a yellow sticky note on them. This one we’ll call “nominal” or “supposed to be.” But then we need a -.002” (minus two thousandths) container, a -.004”, and God forbid there be a need for a -.006” container. Do this with + (positive) +2 +,4, and + ? thousandths as well. It’s okay that not all the bullets are exactly the same as far as the whole batch goes. We just want to have a specific bearing length per trip in the field/range/match so they all have as near identical MV as possible.
In this next picture are my two bodies (holders,) two 30 cal bullet comparator inserts and in the center is my headspace/bump gauge which is used to measure from the head of the case to the datum of the shoulder- See Chapter One: Brass Prep
Next we have the comparators installed and aligned on the caliper jaws in the picture below:
and finally the bearing surface actually being measured (below)