Measuring CBTO. Consistently inconsistent

[michiman]

Hello all,

I recently purchased some Hornady A-tip 153’s. I’m using a Hornady OAL length gauge but I’m having a pretty significant variation in results. Anywhere from 2.6500 to 2.700. It all really depends on how much pressure I apply to the rod. Any advice on getting a more accurate measurement?? How much pressure to apppy?

Thanks

 

[Huskydriver]

@spife7980 where's the link to the video dude lol?

The hornady guage is garbage.

 

[Precision Underground]

I get perfectly consistent results from my hornady gauge. Make sure your caliper is GTG and spin the bullet a little to make sure it’s centered as you measure.

 

[spife7980]

@spife7980 where's the link to the video dude lol?

The hornady guage is garbage.

Wheeler accuracy

 

[Huskydriver]

Wheeler accuracy

Op this is the best and most accurate way for me to get consistent cbto.

 

[daylate]

Wheeler accuracy

This.....might take longer but I feel that it works better for me....

 

[Precision Underground]

I thought the OP was just asking how to measure to the ogive on a round, I was picturing the hornady OAL gauge as the caliper insert, carry on lol.

 

[michiman]

This is great. I’m gonna give it a try. Anyone have any info on how to remove the firing pin and extractor from a Sako TRG? I have never done it before.

 

[ZiaHunter]

Erik Cortina who an excellent competitive shooter has a good video on using the Hornady gauge. I have used it with consistent results for many different rifles. I use the Wheeler method for setting my dies but not have had the best results when determining distance to lands. Use whatever works for you.

 

[918v]

This is great. I’m gonna give it a try. Anyone have any info on how to remove the firing pin and extractor from a Sako TRG? I have never done it before.

Don’t do dat. There are simpler ways of doing this.

 

[michiman]

Don’t do dat. There are simpler ways of doing this.

Please share

 

[918v]

Take a sized case and cut a slit down the length of the neck. Insert your bullet into the neck and push the dummy round into the chamber until it bottoms out. Then push out the dummy round with a cleaning rod. The rifling will seat the bullet.

 

[Precision Underground]

Exactly where you barely start touching the lands is really not information that you have to have. As long as you know where your jam is, you know to not make any bullet longer than that. You still have to load test and decide what shoots best. Knowing the jam number, which the hornady OAL can easily give you, gives you a ceiling that you know not to go past and a reference to chase when the lands move. If I know my jam is 2.35, I am going to do OAL length tests at .010 or .020 intervals until I find what shoots best. All you need is a reference number. It doesn’t matter if the reference is the jam number or the barely touching number. That’s all IMO anyway.

Of course jamming can increase pressure so make sure you know what you are doing.

 

[spife7980]

And I would say that knowing where your “jam” point is not really important information. That’s an arbitrary number. Unless you know where the lands start then you have no idea how much you are jamming them.
Knowing the touch point gives you a benchmark that is exact, it allows for repeatable measurements that don’t depend on “maybe I pushed it harder or softer last time”


If you want to jam go for it, I just wouldn’t say that it’s the metric that matters. I’d say it’s the metric that matters least to me.

Forming dasher brass I had my bullets jamming .2 into the lands. It was tough but still functional. Seated them a bit deeper to .1 of jam since that much just wasn’t necessary and could work the bolt just as easily as I could with .020 of jam. Jamming is arbitrary, it really doesn’t tell you much.

 

[Precision Underground]

And I would say that knowing where your “jam” point is not really important information. That’s an arbitrary number. Unless you know where the lands start then you have no idea how much you are jamming them.
Knowing the touch point gives you a benchmark that is exact, it allows for repeatable measurements that don’t depend on “maybe I pushed it harder or softer last time”


If you want to jam go for it, I just wouldn’t say that it’s the metric that matters. I’d say it’s the metric that matters least to me.

Forming dasher brass I had my bullets jamming .2 into the lands. It was tough but still functional. Seated them a bit deeper to .1 of jam since that much just wasn’t necessary and could work the bolt just as easily as I could with .020 of jam. Jamming is arbitrary, it really doesn’t tell you much.

You are missing my point. I’m not saying the jam number is more important. I’m saying the important number is what shoots well in relation to the jam or the kiss. A few others were bashing the hornady gauge as if it is an inferior way to load. As you said, it’s an arbitrary number.

You still have to run tests to know what shoots best. That’s the number that matters. Whether that number is .020 jammed or .020 off of fully jammed it does not matter. Whether you know the jam number or the kiss number, it’s just a reference to follow as the lands move forward.

I measure the fully jammed number because as the lands move you can take a new measurement in 2 minutes rather than having to disassemble your bolt and spend 30 minutes trying to split hairs while finding the kiss number. All you need is a reference to follow. So when I find the length that shoots best I note it as “jam -.020” or whatever it might be. Then as the lands move I can quickly remeasure where the jam is and back off it the correct number.

For the hornady tool- Sure if you ram the crap out of it one time and not the second time you will get vastly different numbers. But it’s really not that hard to apply a normal amount of pressure and come up with consistent numbers.

 

[michiman]

Take a sized case and cut a slit down the length of the neck. Insert your bullet into the neck and push the dummy round into the chamber until it bottoms out. Then push out the dummy round with a cleaning rod. The rifling will seat the bullet.

Do you have an example? Or a video?

 

[918v]

Do you have an example? Or a video?

 

[Deleted member 10043]

First, did you check the bullets for variation? Also, you can just measure several times and get the average. That'll work. Come to think about it there is probably an acceptable SD and extreme spread thread on this topic, lol.

 

[michiman]

First, did you check the bullets for variation? Also, you can just measure several times and get the average. That'll work. Come to think about it there is probably an acceptable SD and extreme spread thread on this topic, lol.

I used the same bullet and measured about 10 times. With variance of 2.650-2.700.

Are you implying measuring cbto with multiple bullets?

 

[Deleted member 10043]

Never mind. Just realized you are using the same single bullet. My bad. Nevertheless...

2.675

I'm having trouble calculating the average.