Seating depth & velocity variation. Is this normal?

[Boatschool02]

6mmBR. 30" Brux / 95VLD-H / 30.0 Varget / CCI 450
Hard Jam = 0.000
Seating variance working back from 0.006 in 0.003" increments.
Interesting to see the group shift down at 0.018, start opening at 0.021 and then DOUBLE in size at 0.024 off even though the ES for 0.021 & 0.024 were 7 and 5 respectively.
-
Shooting and reloading concessions that can skew my results:
- 42x with a Phoenix Bipod and squeeze bag... I'm causing +/- 1/8" of movement, shot to shot
- Charges weighted with Gempro 250... which is only so-so
- Not yet using a custom FL resize die
- Primers seated on Forster Coax. Will be able to assess 21st century seater impact next session.
- Shots fired about one per minute. HV contour mildly warm when complete.
- Labradar chrono
- Green line represents the average velocity of three shot groups
- ES opens up considerably to the right.

Just wondering if others have observed similar results when graphing velocity vs seating depth?
Is this confirmatory data for jamming VLD bullets? (Would the graph flip and converge to the right with a notoriously jump tolerant bullet?)
Anyone actually inform load decisions based on this info or do most run with Mr. Cortina's methodology which prioritizes vertical consistency in and between groups on the target?
Thanks,
Luke

 

[GrocMax]

Yup, longer jump = faster. To verify shoot enough of each depth (3? 5? more?) to feel comfortable with the data, .000". .010" jump, .020" jump, .030" jump significantly faster each step. The expansion ratio is getting larger.

 

[RonAKA]

My gut feel is that you may be just looking at normal random variation in velocity. Berger recommends taking much larger steps in jump of VLD bullets to find the optimum.

 

['Freak]

http://bulletin.accurateshooter.com/2016/11/how-changes-in-cartridge-oal-can-alter-pressure-and-velocity/

Or the whole shootin’ match …
http://www.bergerbullets.com/effects-of-cartridge-over-all-length-coal-and-cartridge-base-to-ogive-cbto-part-1/

&&
http://www.bergerbullets.com/effects-of-cartridge-over-all-length-coal-and-cartridge-base-to-ogive-cbto-part-2/

&&
http://www.bergerbullets.com/getting-the-best-precision-and-accuracy-from-vld-bullets-in-your-rifle/
Finds with fewer shots fired the vicinity from within to begin testing using smaller increments, like .003”.

 

[foxguy]

http://bulletin.accurateshooter.com/2016/11/how-changes-in-cartridge-oal-can-alter-pressure-and-velocity/

Or the whole shootin’ match …
http://www.bergerbullets.com/effects-of-cartridge-over-all-length-coal-and-cartridge-base-to-ogive-cbto-part-1/

&&
http://www.bergerbullets.com/effects-of-cartridge-over-all-length-coal-and-cartridge-base-to-ogive-cbto-part-2/

&&
http://www.bergerbullets.com/getting-the-best-precision-and-accuracy-from-vld-bullets-in-your-rifle/
Finds with fewer shots fired the vicinity from within to begin testing using smaller increments, like .003”.

Freak, thanks for posting the links. I see I have a lot of reading to do as I too am interested in this.

 

[Zero333]

Can't determine the true average velocity with only 3 shots.

10 shots is what I consider good enough for a dependable average.

 

[Boatschool02]

Can't determine the true average velocity with only 3 shots.

10 shots is what I consider good enough for a dependable average.

Thanks for the input.
Will work to collect more data on subsequent seating depth tests.

 

[fm1947]

Are you measuring seating from ogive or from tip of bullet, for your seating depth ??

 

[savagedasher]

The more you push the bullet back it is like adding more pressure . Your takeing away from used case capacity . Larry

 

[Boatschool02]

Hello,
Measurements to ogive with hornady comparator. Wilson inline seater.
Thanks,

 

[FrankG]

The more you push the bullet back it is like adding more pressure . Your takeing away from used case capacity . Larry

It can but not usually. Usually the more you jam the bullet or closer to the throat/rifling it drives pressure up more. The more you jump it the more it drops the pressure.

Unless your running a pressure test barrel you don't always know though.

Later, Frank
Bartlein Barrels

 

[savagedasher]

It can but not usually. Usually the more you jam the bullet or closer to the throat/rifling it drives pressure up more. The more you jump it the more it drops the pressure.

Unless your running a pressure test barrel you don't always know though.

Later, Frank
Bartlein Barrels

Frank
A little off topic do you sunnon hone your barrels ? Larry

 

[FrankG]

Frank
A little off topic do you sunnon hone your barrels ? Larry

We always prelapped our barrels before rifling and did it by hand. Sunnen contacted us and asked if we would work with them as they wanted to come out with a honing machine for the gun barrel makers/manufacturers. We did all the R&D for them on the prototype machine. We like it so much we bough 2! Nothing else to say. They are nice. One or two other makers called us and asked our opinion on them. They went and bought one also. It takes the human element out of it.

Later, Frank