Berger's method of finding the right seating depth

[Oldmauser]

I refer to this article:

Getting the Best Precision and Accuracy from VLD bullets in Your Rifle

VLD bullets are designed with a secant ogive. This ogive shape allows bullets to be more efficient in flight (retain more velocity = less drop and wind deflection). While this result is desirable for many rifle shooters the secant ogive on the VLD bullets produces another result in many rifle.

bergerbullets.com

Load 24 rounds at the following COAL if you are a target competition shooter who does not worry about jamming a bullet:
1. .010 into (touching) the lands (jam) 6 rounds
2. .040 off the lands (jump) 6 rounds
3. .080 off the lands (jump) 6 rounds
4. .120 off the lands (jump) 6 rounds

Why are they using COAL and not CBTO in their recommendation? If I perform the test using CBTO as reference, would it destroy the whole concept?

 

[Tokay444]

Both are simply used as reference dimensions for the method. Use whichever you’d like.

 

[salks]

This is from second paragraph of your link. They just call COAL, Base to ogive which would be the bearing surface I believe.

For years we encouraged shooters to use a base of cartridge to end of bearing surface OAL (I will use the term COAL to represent this dimension) which allows the VLD to touch the rifling or to be jammed in the rifling.

 

[Oldmauser]

You mean that COAL in Berger's version is the CBTO?

 

[Tokay444]

You mean that COAL in Berger's version is the CBTO?

Did you read the actual page, or the quote in your thread from the page?

 

[salks]

I think for the link you posted yes, they are saying COAL is the back of case to end of bearing surface which would be where ogive begins. If you read some of the other stuff on their site they talk about COAL and CBTO. The person who wrote that though, made it clear what they were talking about.

https://bergerbullets.com/wp-content/uploads/2013/03/COAL.pdf

 

[phlegethon]

It doesn’t matter, just be consistent. Also, that is for the VLDs, not the hybrids. The hybrids are less jump sensitive, though many find they shoot best around 70-80 from the lands. Read the articles on bullet jump at precisionrifleblog.

 

[Rocketmandb]

It doesn’t matter, just be consistent. Also, that is for the VLDs, not the hybrids. The hybrids are less jump sensitive, though many find they shoot best around 70-80 from the lands. Read the articles on bullet jump at precisionrifleblog.

I'd go so far as to say that some of their hybrids essentially care not for seating depth (within a realm of reason). I'm currently at about 1k 105 hybrids through my 6 BRA. I have experienced no loss in group size. I finally got around to measuring how much erosion there's been, and (give or take due to inaccuracies in measurement) it came out at about 15 thousandths.

 

[phlegethon]

I'd go so far as to say that some of their hybrids essentially care not for seating depth (within a realm of reason). I'm currently at about 1k 105 hybrids through my 6 BRA. I have experienced no loss in group size. I finally got around to measuring how much erosion there's been, and (give or take due to inaccuracies in measurement) it came out at about 15 thousandths.

I didn't want to start another argument by making too strong a statement, but I suspect the same. In particular, looking at the data from the famous PRB article, what I really see is just noise, and it would take more than a few three round groups to convince me that this bullet really cares about seating depth at all (it would be even clearer if they plotted the magnitude of displacement instead):

 

[DellaDog]

Well I will say with 105 Hybrids and about 900 rounds (BRA) on the barrel I decided to test seating at depths other than my typical 010-020. I stumbled on a very tight fairly wide node that shot better than any previously. It was -070 to -085.

That was before I read this article.

 

[salks]

Bullet Jump Research

www.shortactioncustoms.com

This is from short action customs web site. If you scroll down on the page they talk about jump. One of things i found interesting in the summit interview with Mr. Gordon is the "jump node" of a bullet stays the same for different calibers and different charges.