Bullet jump tuning

[Harvey_NW]

Interesting article with lots of awesome data from highly accredited shooters about seating depth tuning. Pretty conflicting with traditional ideologies of finding a reliable long range load. Will definitely be integrating new methods in my load development.

Bullet Jump Research: Executive Summary & Load Development Tips

This is the last post in a series of articles focused on bullet jump research that has been conduct...

precisionrifleblog.com

 

[JFK]

Good read. Thanks for posting.

 

[AK_Skeeter]

Jump can depend on the type of bullet your loading.
Barnes recommends a jump 0.050" - .125" off the lands.
In rifles that have long throats Barnes found it was not uncommon
to find the best accuracy with a jump of .200” or more
Other bonded hunting bullets may do better seated closer to the lands.

I like bench rest champion Eric Cortina's approach,
where the relative distance is more important than the absolute distance.
His approach is to resize a fired case, load a dummy road and
find the Cartridge Base to Ogive distance to jam.
Then back seating depth off .020" off jam and
find the best node by incremental bullet jumps:

 

[rayporter]

Eric it a hell of an F class shooter but i have never seen him shoot a benchrest match.

benchrest is much different that F class.

it might be that F class is closer to a hunting scenario.
.

 

[Marble]

I read an article several years ago that explained this, but more in the sense of attempting to shorten the reloading process to find the round that works best for your gun.

I've used this method, finding seating depth first, then switching to different powders. It has worked well and I've been surprised at the results.

After getting a load figured out, I would start messing around with seating depth again to see if anything changed. Sometimes it needed fine tuning but mostly it was super accurate.

Sent from my SM-G986U using Tapatalk

 

[AK_Skeeter]

I read an article several years ago that explained this, but more in the sense of attempting to shorten the reloading process to find the round that works best for your gun.

I've used this method, finding seating depth first, then switching to different powders. It has worked well and I've been surprised at the results.

After getting a load figured out, I would start messing around with seating depth again to see if anything changed. Sometimes it needed fine tuning but mostly it was super accurate.

Sent from my SM-G986U using Tapatalk

Erick Cortina explains this well in his video.
Variation in velocity (too high standard deviation/extreme spread) = inconsistent combustion problem..
work on primer, powder type or charge, case capacity variatiion, neck tension, etc.

Low extreme spread/standard deviation but poor groups = barrel harmonics problem.
work on bullet seating and/or barrel tuner

 

[lyle_destroys]

Erick Cortina explains this well in his video.
Variation in velocity (too high standard deviation/extreme spread) = inconsistent combustion problem..
work on primer, powder type or charge, case capacity variatiion, neck tension, etc.

Low extreme spread/standard deviation but poor groups = barrel harmonics problem.
work on bullet seating and/or barrel tuner

I've never though about that but it makes a lot of sense.

 

[Marble]

Erick Cortina explains this well in his video.
Variation in velocity (too high standard deviation/extreme spread) = inconsistent combustion problem..
work on primer, powder type or charge, case capacity variatiion, neck tension, etc.

Low extreme spread/standard deviation but poor groups = barrel harmonics problem.
work on bullet seating and/or barrel tuner

Good to know thanks!

Sent from my SM-G986U using Tapatalk

 

[Harvey_NW]

Erick Cortina explains this well in his video.
Variation in velocity (too high standard deviation/extreme spread) = inconsistent combustion problem..
work on primer, powder type or charge, case capacity variatiion, neck tension, etc.

Low extreme spread/standard deviation but poor groups = barrel harmonics problem.
work on bullet seating and/or barrel tuner

I'm definitely familiar with Cortina's methodology and information but the data in this article both highlights, and disproves parts of his approach. Which is why I posted this. A lot of Cortina's advice is based on his personal methodology loading F-class rounds in extremely custom competition rifles. This data was from multiple combinations of shooters, calibers, and bullets, that disproves some of the old theories and actually identifies a statistical advantage of finding a forgiving window farther off the lands.

 

[wind gypsy]

Cortina to Randy?

 

[Hill Difficulty]

In 2018 I paid SAC/Mark Gordon (featured in OP's link) to build me a barreled action in 6CM. He instructed that I seat 105 VLDs at .070" jump, then work on charge. He politely insisted my setup to be (not should be) extremely accurate based on how he put things together. He was right. It only took a handful of VLDs to determine charge (have since moved on to 108 EHs, same jump). The rifle's accuracy/consistency has been very impressive.

 

[cooperjd]

very interesting, thank you

 

[Harvey_NW]

In 2018 I paid SAC/Mark Gordon (featured in OP's link) to build me a barreled action in 6CM. He instructed that I seat 105 VLDs at .070" jump, then work on charge. He politely insisted my setup to be (not should be) extremely accurate based on how he put things together. He was right. It only took a handful of VLDs to determine charge (have since moved on to 108 EHs, same jump). The rifle's accuracy/consistency has been very

I'm maybe a novice level reloader, but I like to go full send and geek out on whatever it is I'm doing. My mentor advised that I don't get caught up in the hype of jamming or staying close to/chasing lands. Coincidentally through my own development I found a window from roughly .050-.100 off the lands in my 6cm with 105 bergers that consistently shoots avg 1/2 moa, and it's just a Ruger American Predator I bought to practice and learn with. I figured it was a fluke until I read this article!

 

[Hill Difficulty]

I'm maybe a novice level reloader, but I like to go full send and geek out on whatever it is I'm doing. My mentor advised that I don't get caught up in the hype of jamming or staying close to/chasing lands. Coincidentally through my own development I found a window from roughly .050-.100 off the lands in my 6cm with 105 bergers that consistently shoots avg 1/2 moa, and it's just a Ruger American Predator I bought to practice and learn with. I figured it was a fluke until I read this article!

From the PRB series on the jump testing, the easy takeaway for me (that proved true) is that A LOT of 6 and 6.5 Creedmoor rifles do well with a jump at .060" to 070" and to load with H4350. Seems if a Creedmoor chamber/throat is cut w/enough jump can load at SAAMI length and be in the optimum accuracy ballpark + no issues w/magazine COAL.

Of course, the powder and jump consistency thing that works for Creedmoor cals does not apply to other cartridges. My other calibers are all over the place on seating, most either near the lands or jammed a bit.

[edit: ...does not necessarily apply to other cartridges.]