6.5 CM CBTO measurement

[gjb89]

Fairly new to reloading and I am measuring the cartridge base to the ogive/lands junction with the hornady OAL gauge and mitutoyo calipers. I'm getting a spread of readings from 2.2185" to 2.2495" with the 140 GR Hornady ELD-M. Rifle is a Defiance action and BT barrel. Any of these numbers look ok? Also how far off the lands are you loading the 140gr ELDs?

 

[Ned Ludd]

You should be able to get reproducible numbers with the Hornady OAL gauge. Typically for 10 measurements with the same bullet, I would expect no more than average +/- .002" with a little practice, probably even better. Your are currently talking about a total variance of .031" from high to low, which is totally unacceptable for use in seating depth determination. My suggestion would be to practice using the tool with a single bullet, learning to feel the light "touch" when it first encounters the lands, until such time as you can routinely and reproducibly obtain the same measurement +/- .001" or .002".

 

[Dusty Stevens]

That doesnt sound right for a comp match. What size insert are you using?

 

[RegionRat]

Agree with the others... that your reading variation is way too large.

To be clear, are you measuring your CBTO on a cartridge, or taking readings on the rifle’s chamber?

Many times the details of the chamber reamer can make getting a steady reading on the rifle a challenge, but if we are talking cartridges something went wrong.

 

[BeefyT11]

Hornady told me that they have heard a lot of great feedback with that bullet shooting .015 to .030 off the lands

 

[JFrank]

What’s the difference between a 6.5 Creedmoor and a 6.5 comp match?

 

[Bc'z]

What’s the difference between a 6.5 Creedmoor and a 6.5 comp match?

Marketing!!!!!
I looked it up once, it just never took off also comes in 6mm.

 

[JFrank]

No difference in chamber?

 

[Bc'z]

No difference in chamber?

Yes, I tried to bump a thread for ya, but not seeing it.
Search 6mm competition match.

 

[JFrank]

I think I got it
The Creedmoor is based on a 30 TC
The CM is from a 243 parent case
J

 

[gjb89]

That doesnt sound right for a comp match. What size insert are you using?

5-26 insert.

I tried using a little less pressure and I was able to bring the reading alot closer.

 

[McHaggis]

With the 140 ELD-M’s measured with the 5-26 insert my Howa 6.5CM is 2.271” just touching. I’m still playing with seating depth but 0.015” and 0.003” both look good.

 

[Fliers]

I wouldn't expect such a large change even with pressure.
Is this a single bullet giving you this variance, or is this measuring multiple loaded rounds?
Is your neck tension too light? Maybe you are pressing the bullet into the case.
You need to spin the bullet a little to get it flat and parallel on the base of the calipers.

If separate rounds, perhaps your neck tension is too high and you are getting variance in actual seating depth from brass hardness differences.
I noticed my gauge was cutting into the bullet a little as I tried to spin it to get minimum measurement. I took my chamfer tool lightly to it to take away the sharp edge. Helped with consistency.

 

[Dusty Stevens]

Since its based off the 243 case with the main changes being a 31deg neck pushed forward you should be getting the same ctbo measurements that you would get with a 260

 

[Bc'z]

Just finished loading 50 of the Carolina load.
140 grain berger vlds, sorted bbto
2.80 coal
2.155 cbto

143eldx un sorted
2.8315 coal
2.2005 cbto

260 rem
130 berger ar hybrids sorted
2.0030 cbto
2.8105 coal.
I put 260 up as referance only.
Its coal is longer by .01 compared to
140 berger

And all these #'s only mean anything to me and my gear.
Your comparitor might be a hornady as is mine, but there are variables in manufacturing and your finger pressure vs mine.
Just as in bullets from lot to lot it's why we sort. Hope this helps you a little in understanding.

 

[Dusty Stevens]

Just finished loading 50 of the Carolina load.
140 grain berger vlds, sorted bbto
2.80 coal
2.155 cbto

143eldx un sorted
2.8315 coal
2.2005 cbto

260 rem
130 berger ar hybrids sorted
2.0030 cbto
2.8105 coal.
I put 260 up as referance only.
Its coal is longer by .01 compared to
140 berger

And all these #'s only mean anything to me and my gear.
Your comparitor might be a hornady as is mine, but there are variables in manufacturing and your finger pressure vs mine.
Just as in bullets from lot to lot it's why we sort. Hope this helps you a little in understanding.

Yours is a creedmoor. Hes loading comp match

 

[Bc'z]

Yours is a creedmoor. Hes loading comp match

Well at least the 260 data wont go to waste