consistent measurement with Hornaday case length comparator.

[goblbustr]

Let me preface this by saying I am new to this tool. When measuring cases I cannot get a consistent measurement. Spin the case inside the comparator and you get measurements that vary by .003 or more. This is brand new Lapua brass and brand new Peterson brass. I bought this to check my shoulder bump but with these results its pretty much useless. Any ideas what I'm doing wrong?

 

[Fullbore92]

What brand of calipers are you using?

 

[LRNut]

Let me preface this by saying I am new to this tool. When measuring cases I cannot get a consistent measurement. Spin the case inside the comparator and you get measurements that vary by .003 or more. This is brand new Lapua brass and brand new Peterson brass. I bought this to check my shoulder bump but with these results its pretty much useless. Any ideas what I'm doing wrong?

Are you sure the insert for the caliber you are using is not moving? Is the screw tight? FWIW, I don't have that problem.

 

[crashlanding]

You need to fire the brass to get a starting measurement, it will help to blow the case out

 

[trout004]

Are you sure the insert for the caliber you are using is not moving? Is the screw tight? FWIW, I don't have that problem.

Also, adding to this, making sure the calipers are closed so the gauge contacts the flat part of the caliper on both sides, when it is being mounted makes sure it stays square.

 

[Bob Wright]

You need to fire the brass to get a starting measurement

Yep.

 

[YZ-80]

I use the Hornady OAL guage. About 80% of the time, I get consistent measurements. I don't know how far you are seating off the lands but I'm typically .015 to .020, so I don't typically sweat .003 of variance. I usually take the average of 3 to 5 measurements, as long as they are within a 5 one thousandths. One thing to watch out for is that sometimes, with a secant ogive (slimmer bullet) you might not get a "hard stop" when you push into the lands. This may (sometimes) be due to throat errosion and you can be dealing with .050 to .060 of "slop" trying to figure out where the lands are. Very frustrating at times.

 

[MagnumManiac]

These comparator tools are only as precise as you are using them…
If you are turning the case and it is reading different, you may have dodgy callipers or nicks, bent rims or other damage on your brass.
The best measuring tools I have found and use are RCBS Precision Mics, they will show you between .001" variation in your brass. It is not marked to show 'tenths' but is easy to see in between the hash marks.
You need to take averages from several pieces, not just one.

Cheers.

 

[sedancowboy]

One trick I have learned is to take a deburring tool and lightly chamfer the comparator. It will increase consistency by a lot.

 

[Ryeguy]

Make sure battery is good on calipers.. My guess would be faulty calipers.

 

[Phil Rizzo]

The Hornady inserts aren't famous for perfectly round holes. Beware.
Always use the exact same insert, they can vary quite a bit even though stamped with the same numbers.
Shoot the brass until you can feel tension closing the bolt on a fired case. Hopefully your first firing is a reduced load, at least 5% off published maximum charges for case life consideration. It may take more than 1 firing.
Once all the cases form to your chamber length, the headspace measurement will be more consistent.
Then try to bump the shoulder 1.5-2 thousandths, average. They should chamber like you need them to. Good luck, and remember it's best to average measurements of multiple cases for a "target" number.

 

[huntinghuasna]

No batteries required. 1.5581"…?

 

[VinceMule]

If you use a fire formed case, drill and tap the back end, you will be in a different world when it comes to getting uniform results with the Hornady. Hornady was slick when they made the drill size and tap a bastard size.

 

[bluedog69]

Let me preface this by saying I am new to this tool. When measuring cases I cannot get a consistent measurement. Spin the case inside the comparator and you get measurements that vary by .003 or more. This is brand new Lapua brass and brand new Peterson brass. I bought this to check my shoulder bump but with these results its pretty much useless. Any ideas what I'm doing wrong?

Probably nothing wrong. You do have to spin the case until you get the shortest measurement to make sure the case is in perfect alignment.
Just like measuring COAL you spin the shell until you know the base is flush with the tool. If it is a little crooked it will measure longer.
If you want to go to a whole other level some guys take out the ejector spring and pin and seat bullets into the lands to make sure the brass is being pushed back against the bolt face as it is fire formed the first shot. This minimizes case stretch in the base area and lengthens case life. No case head separation down the road.
You do need to fire form it and may have to fire it twice without any shoulder bump at all to get them stretched to where they are tight and don't want to go back in the gun after being reloaded.
A tight tight shell is what you want to get your measurement off of. Then figure out where .0015 or .002 is at when you resize.