Do Ladder Test or CBTO Test First

[lgwatson]

I am developing loads for 6.5X47 Lapua. Should I ladder test first and then look for a good CBTO or do the CBTO test first?

 

[seymour fish]

I am developing loads for 6.5X47 Lapua. Should I ladder test first and then look for a good CBTO or do the CBTO test first?

Ladder first, using some middle of the road seating depth, say .020 off. Avoids the question whether some typical powder chg might be too hot for your rifle, as you monkey with seating depth

 

[mikecr]

If '.020 off' happens to be a really bad place, then you'll be interpreting your powder through a shotgun pattern..
And if you're going for best accuracy, which is what a ladder is for, better pay attention to both horiz and vert.
Vertical only is more of an OCW quest, which is often not most accurate, but most forgiving.
The optimum choice here shifting with distance and shooting format.

I vote CBTO first, full seating testing as recommended by Berger(works for any brand/bullet).
Can do this during fire forming of brass.
Then move to powder
Then tweak seating in it's window for group shaping
Then if this is a hunting gun, test and adjust powder for a best cold bore ACCURACY result (not the same as hot bore grouping).

 

[group therapy]

what is cbto?

 

[bloc]

what is cbto?

Cartridge Base To Ogive

 

[group therapy]

Cartridge Base To Ogive

thank you

 

[Lou Tenant]

Here's an interesting article from sierra :

https://sierrabulletsblog.com/2014/07

 

[dsculley]

I agree with Mike, especially if you are shooting VLD type bullets. Run the Berger test then load development. Once you find your load you might tweak the seating depth. I prefer the OCW test to the ladder test. Done correctly they will lead you to the same place but 1 errant shot in a ladder test can lead you to the wrong place.

 

[Jet]

Ladder first with bullet in the lands a good bit but not hard as to cause a stuck bullet if extracting an unfired case. Pick the powder charge you want to shoot based off the ladder then start adjusting seating depth out in .003 increments. Once you settled on a seating depth try different neck tension.

Good shooting

Rich

 

[lgwatson]

I agree with Mike, especially if you are shooting VLD type bullets. Run the Berger test then load development. Once you find your load you might tweak the seating depth. I prefer the OCW test to the ladder test. Done correctly they will lead you to the same place but 1 errant shot in a ladder test can lead you to the wrong place.

What is the OCW test?

 

[memilanuk]

What is the OCW test?

Here ya go...

 

[mikecr]

Ladder first with bullet in the lands a good bit but not hard as to cause a stuck bullet if extracting an unfired case. Pick the powder charge you want to shoot based off the ladder then start adjusting seating depth out in .003 increments.

The moment you clear the lands with seating adjustment here, you will completely invalidate what you had considered with your ladder(while ITL). So then you might re-reun a ladder, with bullets OTL. I used to, now I just test seating first.
You gotta know bullets in the lands(ITL) cause higher starting pressure, which influences everything about powder burn rate and barrel timing. This may be known to be what you desire, like with a 30br or other underbore, but way less likely with a normal hunting capacity cartridge.

 

[mikegaiz]

Ladder first, but not seating the bullet in the lands. In the lands will show pressure early and you will miss the harmonic. VLD's need to be jumped at least 10 off, usually 20 to 30.

 

[tuttlefarm]

CBTO............

 

[Jet]

Starting in the lands has not proven to me to invalidate ladder test results. It creates a base line for further tuning/development. A couple things I didn't add to my post above that maybe I should have.

- I always reevaluate tune windows through ladder tests throughout the life of the barrel. The powder charges in the "flat spot" will be reshot with the seating depth settled on previously to verify it is still the correct charge weight.
- Once that is verified or tweaked another seating depth test is accomplished. This is done to adjust for throat erosion. As the throat erodes I usually have to bump up powder charge slightly (still staying in the window) to keep the accuracy. Each barrel erodes differently. The barrel I shot at the NBRSA NW Regionals has 700rds through it and has eroded .040" since new. That's double what I normally experience with a Dasher. This barrel shoots very well but staying on top of it's tune takes more effort.

Regardless of the method used anyone seeking to get the best potential from their rifles needs to be methodical in their approach, check/test all variables and keep detailed notes.

Good Shooting

Rich

 

[barefooter56]

I am developing loads for 6.5X47 Lapua. Should I ladder test first and then look for a good CBTO or do the CBTO test first?

Try finding the bullet seating depth accuracy node first http://www.bergerbullets.com/vld-making-shoot/ . This will help also :http://www.bergerbullets.com/effect...coal-and-cartridge-base-to-ogive-cbto-part-1/
and
http://www.bergerbullets.com/effect...coal-and-cartridge-base-to-ogive-cbto-part-2/
Any bullet seating depth testing should be done at the lowest powder charge listed for the bullet/powder/cartridge combination you are testing. Once the bullet seating depth accuracy node is found. Work the load back up slowly checking for pressure signs and accuracy until your highest velocity accuracy node is found.
There are many ways to do load testing. This is just one that I use. Hope this helps.
Take care,

 

[mikecr]

That's why you can do full seating testing during fire forming(which also should be done prior to powder testing).

 

[jerseyjoe]

I'm not a competition shooter, but I have found that establishing the most accurrate bullet seating depth (CBTO) first will also be the most accurate load when testing for the optimum charge weight.

This works only if you are not constrained by magazine length.

 

[CharlieNC]

Well I run them both simultaneously using a proper "matrix" combination. Five charge weights plus five seating depths yields nine different loads.

 

[mtncwru]

Well I run them both simultaneously using a proper "matrix" combination. Five charge weights plus five seating depths yields nine different loads.

Can you share more detail on your methods here, Charlie? Off the top of my head I would expect 5 different charge weights and 5 different seating depths to produce 25 different loads to test.

I'm definitely interested in making the most of my range time, so any way to make my load development more efficient I'm all for!