Advice on using Hornady OAL gauge

[aggiejet]

I just bought a Hornady OAL gauge and a set of bullet comparators. I attempted to use them for the first time today and I am a little bewildered at the results. I used two different bullets and took 10 measurements using each bullet. I got a divergence (difference between longest and shortest measurements) of .080 with one bullet and .120 using the other one. I was expecting to see only .001 or .002 difference between measurements.

To the best of my ability I am following the directions; lightly (using 2-3 pounds of pressure) pushing the plastic rod to seat the bullet ogive against the lands/grooves then locking the thumbscrew and removing the case/bullet for measure. It looked simple enough on all the YouTube videos I watched. The rifle is a Savage 111 25-06.

I measured three different Hornady factory cartridges. It was very interesting to note that there was .076 difference between the shortest and longest (3.680-3.604) as measured from base to the ogive.

I think there is a lot of merit to using a tool like this to make cartridges to fit your rifle. I look forward to using it properly.

Thanks for help,
Mark

 

[RAT807]

I like to spin the round or bullet as to center the object being measured. You also need to be aware of how you secure it to the caliper and how far away from the tip you anchor or secure it.
I put the set screw on the flat side of the blade on the thickest part. I think it gives me more area to center the object being measured, vs the knife edges at the tips. The blades are knife edged for a short distance from the tips, then go to a larger flate area. I mount the comparator on the blade that slides and hold the round upside down to measure it. It's easier to spin the round this way as it rests in the hole of the comparator

 

[fguffey]

I measured three different Hornady factory cartridges. It was very interesting to note that there was .076 difference between the shortest and longest (3.680-3.604) as measured from base to the ogive.

I have the bent tool, I have 4 test cases that screw into the tool and hold the bullet, I do not use it but I have it.

I drill the flash of a fired case hole/primer pocket to a diameter that accommodates a cleaning rod. After drilling the flash hole/primer pocket I neck size the case. I want all the bullet hold I can get, I do not want bullets moving.

After seating a bullet I remove the bolt then chamber the test round, after chambering the test round I use a cleaning rod to push the bullet out of the case. When the bullet contact the rifling I quit pushing the bullet.

Instead of measuring the length of the test round from the rifling contact point to the head of the case I install the test case into the shell holder and raise the ram to the top.

Next, I adjust the seating die to the test case. After adjusting the seating die to the test case I measure the height of the seating stem. The height of the seating stem indicates 'ZERO"' off the lands. If I want ..035" off the lands I lower the stem .035".

If I do not want to start over the next day I save the test case.

F. Guffey

 

[bush3755]

With that much spread in your measurements, try measuring the same loaded round several times. If you don't get the same reading every time, you're not using your tools the same way each time.

As bullet's ogives are not all shaped exactly the same, it's normal to have bullets seated to a few thousandths inch spread as measured to some reference. That's not enough to get concerned about because the barrel's rifling wears away from normal erosion from burning powder. And very little force is needed to move the bullet another thousandth deeper into the rifling whose angle is only one or two degrees relative to the bore axis. The distance from the point where the bullet touches the rifling to its tip also has a few thousandths (or more) spread; but where the tip is doesn't matter anyway because it touches nothing but the air it goes through and the target.

The .25-06 case shoulder stops against the chamber shoulder when it fires. So, the distance from the chamber shoulder to some reference point on the bullet determines how far it jumps to the rifling when fired. Case dimensions from head to the shoulder will vary a few thousandths, so their shoulders won't be at the same place when seating bullets in conventional seaters. Whatever the spread is in case headspace (head to shoulder) will be transferred to the bullet jump distance.

The case head's away from the bolt face by a few thousandths and it's not the same for every shot fired. Only when bullets are seated out far enough to jam into the rifling when seated does the case head bear against the bolt face. Even then, sometimes the spring loaded ejector in the bolt face pushes it away a little bit if the bullet's not gripped tight enough by the case neck.

This all adds up such that even with bullets seated to a few thousandths spread measured to the case shoulder, their spread to the case head is typically more.

It's not all bad news. Extremely accurate ammunition can have several thousandths spread in its jump distance to the rifling. Commercial match ammo's got that much and it shoots very accurate in good barrels.

 

[gamestalker]

I have been doing it very much like Fguffeydoes. I can't really say I've discovered a more accurate manner of determining where zero is, and how far off the lands I'm seating.

Once I determine zero for each bullet and rifle, I log the seating stem zero measurement, which saves me a bunch of time next time I load using that same bullet for that rifle.

GS

 

[aggiejet]

What a great idea. What you describe is the heart of what I am trying to learn about. I find it difficult to find the point where the bullet is just touching the lands. I can sometimes feel the bullet "snap" into place. And really without using any force.

What I find intriguing about your process is the fact that you have sized your neck, which I think would make pushing the bullet to the lands more of a challenge because of the resistance of the bullet and the neck.

Hornady intentionally makes their test case a little larger so the bullet can travel freely, allowing the user to be able to find the lands with a degree of finesse. I am not able to due that with any reliability, as noted in the 10 measurements I made using the Hornady Bullet Comparator and a 117 gr SST bullet: 3.658, 3.640, 3.653, 3.672, 3.684, 3.660, 3.672, 3.714, 3.718, 3.720

For reference, a Hornady factory cartridge of the same bullet measures 3.660.

Thanks for the replies. Always learn a lot from you guys

 

[bush3755]

Seat your bullets relative to the case shoulder if you want them to have a consistent jump to the rifling. The case shoulder is the only thing on all .25-06 rounds that's at the same place in the chamber when they're fired. Case head and mouth have a few to several thousandths spread relative to the shoulder. Measure them to see how much.

I think the least amount of bullet grip by the case neck suitable for handling and functioning is best for accuracy. Muzzle velocity spread is smaller with less grip.

 

[aggiejet]

Seat your bullets relative to the case shoulder if you want them to have a consistent jump to the rifling. The case shoulder is the only thing on all .25-06 rounds that's at the same place in the chamber when they're fired. Case head and mouth have a few to several thousandths spread relative to the shoulder. Measure them to see how much.

I think the least amount of bullet grip by the case neck suitable for handling and functioning is best for accuracy. Muzzle velocity spread is smaller with less grip.

So how do you determine what the proper amount of jump is for any particular rifle? I thought that was the beauty of the Hornady OAL gauge (or a similar device) was that it could determine the jump for a specific rifle and a specific bullet.

Can you describe the process and tools you use for measuring from the case shoulder?