CBTO measurement

[Totosdad]

I loaded some 308 Nosler 150 grain Accubond to SAMMI specs.
wanting to improve my grouping, I began measuring CBTO,
I am getting way different measurements, checking 5 times.
Am I pushing the rod on the Hornady seating depth tool to hard?

[Dave Hoback]

Possibly. Tough to really say without seeing your tools & technique. Do you mean you’re getting different measurements on each same loaded round? I ask because if you are talking about different bullets, yes, they will have different measurements. I measure ogive as well and can only say if you get different values on the same cartridge, it’s either the measurement tool or user error.

[Full Chisel]

Agree with Dave. Can you give a little more detail on your process as I am also not certain I understand what measurement technique you're using. When you say the Hornady seating depth tool rod, if it's what I think it is, I'm confused as to how you're using that for CBTO. If you're getting different CBTO between say a 150 accubond and 168 Hornady ELD, then that would be quite normal as the bullet profiles are different. But, if you're getting way different CBTO between different rounds of the same 150 accubond loads, then something is definitely up. You may see a little difference in the latter just due to bullet to bullet variation and which comparator you're using, but it shouldn't be more than a few thousandths.

Have you checked that your primers are fully seated?

[Robinhood]

There has been a lot of discussion about this in reloading discussions using the Hornady and having an inconsistent feel. I now use the Hornady gauge to get a baseline. I leave the CBTO .020" long then creep into it with my seater die in .002 increments until the bolt closes with little to no effort. I leave that Empty case with the bullet in my die set for future reference.

If you purchase the Hornady modified case you will find it to be a different dimension than your shoulder bumped brass anyway.

[Totosdad]

Not on a loaded round, I am using the Hornady comparator
with a Hornady modified case & The Accubond bullets and I am getting a wide variety of CBTO
measurements.

[Full Chisel]

Repeating the measurement 5X on the same once seated round, correct? Or Are you repeating the measurement on the same round 5X after pulling bullet then reseating it into Hornady test case each time? Did you seat the bullet to the lands like Robinhood was describing above where the rifle may actually do the final seat? Or, are you seating to a different OAL with seating die only? How different are the measurements? Sorry, just a lot to read into this.

[Dave Hoback]

Also, what differences are you seeing? A couple of Thous. Is pretty normal. Especially using a Vernier Caliper. They are not as accurate as a Micrometer. I do typically see a Thou. or haps 2. I always measure at least 3 times and take an average. To me, within a couple Thous. is perfectly fine. Now, if you are seeing .004”, .005”+, well yeah, there is something going on.

[Blue Avenger]

Mitutoyo or harbor freight caliper?

[yobuck]

There has been a lot of discussion about this in reloading discussions using the Hornady and having an inconsistent feel. I now use the Hornady gauge to get a baseline. I leave the CBTO .020" long then creep into it with my seater die in .002 increments until the bolt closes with little to no effort. I leave that Empty case with the bullet in my die set for future reference.

If you purchase the Hornady modified case you will find it to be a different dimension than your shoulder bumped brass anyway.
By using this method, why is the Hornady tool even necessary?

[pdshooter2]

By using this method, why is the Hornady tool even necessary?


so you can measure the finished product( if i read the series correct)
i do the opposite, start short until i see the first marks from all lands.
then back off till i see just touching marks...that disappear if i back off .001.
that is touch..not any jam.

sounds like he needs to PRACTICE to get uniform readings

[Dave Hoback]

Precisely. Actually need a combination of the Hornady Lock-n-load & comparator. I just made my own lock-n-load with aluminum tubing & I thread my own cases.

[yobuck]

so you can measure the finished product( if i read the series correct)
i do the opposite, start short until i see the first marks from all lands.
then back off till i see just touching marks...that disappear if i back off .001.
that is touch..not any jam.

sounds like he needs to PRACTICE to get uniform readings
But didnt you just produce something to measure by chambering the round?
The goal is (what) ?
Why is one method better than another that requires no special tools?

[sharpshooter]

Using a Hornady modified case is probably the culprit. I've seen it numerous times that the case has an oversize neck, not letting the cartridge case seat completely when pushing it in with a bullet.

[PhilC]

I have the Hornady comparator but use a fire formed case that has been drilled and tapped to fit comparator. Frankly, after going through that exercise, I went back to my original procedure as described by Robinhood.

[pdshooter2]

But didnt you just produce something to measure by chambering the round?
The goal is (what) ?
Why is one method better than another that requires no special tools?

the hornady/stoneypoint TOOL is just that a TOOL. it will get you a very close STARTING POINT for finding the lands,,how ever you want it, touch, off or jam.

once you have a starting point you can move in or out to get what you want with a dummy
stoney point with home converter fired case from the original chamber work pretty good...hunter plinker.

no one is forcing you to do it any specific way, don't try forcing us to do it your way.

[GrenGuy]

I use the Alex Wheeler method :(

[yobuck]

the hornady/stoneypoint TOOL is just that a TOOL. it will get you a very close STARTING POINT for finding the lands,,how ever you want it, touch, off or jam.

once you have a starting point you can move in or out to get what you want with a dummy
stoney point with home converter fired case from the original chamber work pretty good...hunter plinker.

no one is forcing you to do it any specific way, don't try forcing us to do it your way.
Well i would fall under the hunter plinker category as well, and im not attempting to force anyone to do anything.
I actually could care less how others go about doing things so long as it makes them happy.
But there are other ways of doing most things, and fact is it isnt always necessary to have a box full of tools and gadgets in order to do some of those things. Having a collection of special cases in order to load ammo is one of them.
Problem is much of the younger or newer shooters never got to learn how to do things like this before somebody created a must have gadget for doing it.
Once the overall length for a specific cartridge/bullet combination is established most of us at least never need to reset it again.
And assuming one might use different bullets requiring a different seating depth, a dummy round in an old case for each bullet works just fine for resetting the seating die. Making things more difficult or complicated dosent necessarily indicate one being more informed.

[South Prairie jim]

I loaded some 308 Nosler 150 grain Accubond to SAMMI specs.
wanting to improve my grouping, I began measuring CBTO,
I am getting way different measurements, checking 5 times.
Am I pushing the rod on the Hornady seating depth tool to hard?
Maybe so, you could insert the modified case as normal then point the muzzle down to allow the bullet to drop to the rifling then adjust the rod carefully. Let gravity do the work.

[pdshooter2]

Well i would fall under the hunter plinker category as well, and im not attempting to force anyone to do anything.
I actually could care less how others go about doing things so long as it makes them happy.
But there are other ways of doing most things, and fact is it isnt always necessary to have a box full of tools and gadgets in order to do some of those things. Having a collection of special cases in order to load ammo is one of them.
Problem is much of the younger or newer shooters never got to learn how to do things like this before somebody created a must have gadget for doing it.
Once the overall length for a specific cartridge/bullet combination is established most of us at least never need to reset it again.
And assuming one might use different bullets requiring a different seating depth, a dummy round in an old case for each bullet works just fine for resetting the seating die. Making things more difficult or complicated dosent necessarily indicate one being more informed.


you can change the tire/wheel on a car with a pair of vise grips and a hammer also.
in spite or your OPINION, just because it works does not mean it is the best way.
using the best tool for the job is what technicians do, back yard mechanics not so much

yes i am a technician, with an education, a lic and a degree.......i try to use the best tool i can afford.

[Dave Hoback]

I do agree in not using the Hornady cases. Like I said, I made my own tool like the C1000 Lock-N-Load. And I tap my own cases to use with it. The cases I actually use. I also don’t use a Mitutoyo Caliper. But I don’t use a Harbor Freight either, LOL! It measures perfectly & repeatedly sighing .001”, which is just fine with me.