Measuring COAL???

[stradibarrius]

I am using a Hornady OAL gage with a Hornady modified case for 6.5cm to measure my Tikka T3 TAC A1. It seems to me that the measurement is dependent on the bullet used when measuring. I used a Berger 140 Hybrid Target and a Hornady 143 ELD X. The average of 10 measurements each was different, but also the measurement to the olive of each was different. That's no real surprise because the difference in the design of the bullets. Here is my question...when trying to seat the bullets to get the jump I want the COAL will not work due to the difference in shape of the bullets. Hornady directions say to measure COAL but it seems you should measure to the ogive???

 

[want2learn]

i believe you're absolutely correct....the ogive is where the projectile will first impact the lands so the measurement will vary based on design/contour of the projectile. i believe the measurement is called COTB where you measure the case from ogive to the base.

It is my impression that Hornady is advocating this specific measurement for a specific projectile.....and should not necessarily reflect the same value for a different projectile

there are several commercially available measuring devices to establish COTB, Hornady and Sinclair among others makes them....i've been using the Forster Datum Dial Kit and am very pleased with it.

there are some nice, quick videos here where Forster discusses this and the use of their tool...the concepts are the same should you choose a different manufacturers device: https://www.forsterproducts.com/product/datum-dial-kit/

 

[straightshooter1]

I am using a Hornady OAL gage with a Hornady modified case for 6.5cm to measure my Tikka T3 TAC A1. It seems to me that the measurement is dependent on the bullet used when measuring. I used a Berger 140 Hybrid Target and a Hornady 143 ELD X. The average of 10 measurements each was different, but also the measurement to the olive of each was different. That's no real surprise because the difference in the design of the bullets. Here is my question...when trying to seat the bullets to get the jump I want the COAL will not work due to the difference in shape of the bullets. Hornady directions say to measure COAL but it seems you should measure to the ogive???

Yes, to get the best measurement for the jump one needs to measure the CBTO (Case Base To Ojive) not COAL (Cartridge Overall Length). There is some correlation between the two and even the well known QuickLoad app will use the COAL measurement for its calculations though the CBTO is more accurate and appropriate.

 

[Steel head]

Tip to beginning of bearing surface can vary drastically even with similar weight class bullets.

 

[stradibarrius]

Thanks for the verification! Logic says it has to be measured to the Ogive.