Big jump or little jump

[Matt Jacobs]

I was doing some testing on a new barrel yesterday (100) rounds. Im fairley new to this stuff so I dont know alot.

I have one load at:
Lapua brass
105 hybrids
30.2 N150
jumping .020

Second load is exact same but jumping .056

Both loads are producing acceptable groups and sd/es numbers
Is there a reason to go with one over another?

 

[FeMan]

I have nothing scientific to add but can say that in my personal experience, I have found that nodes with greater jump seem to be more tolerant of changes to temp and throat erosion and therefore tend to be stable longer. I shoot loads from 0.020" jam to 0.150" jump in various rifles so this is just a general (and somewhat weekly supported) observation. In the end, I shoot the load with the jump that the target approves of. If they are the same, I typically declare the longer jump the winner by tie-breaker.

 

[Eagle Six]

As @FeMan said ^^^^^

 

[Clancy]

Shoot them at distance, one should be better than the other. If not, I’d pick the one with the most forgiveness on either side of it.

 

[Gary C]

I'm kinda new myself.
I started with a factory Savage barrel 8 twist and found it liked Berger 108s
and Sierra 107s and Varget.
I tested them at touch and in the lands .010 and backed out in .002 steps.
In my barrel, the groups opened up some jumping .010 and up.
I got no improvment by backing out of the lands from .010 in and none jamming in
more so I stuck with the .010 in.

I'm testing a new barrel with 68 gr bullets and have started at .010 in.
The powder testing is just starting but i'm getting single digit SDs and groups in the threes with H322
I will move on to seating depth testing when the wind calms down here in New England.

 

[boltfluter]

I'm kinda new myself.
I started with a factory Savage barrel 8 twist and found it liked Berger 108s
and Sierra 107s and Varget.
I tested them at touch and in the lands .010 and backed out in .002 steps.
In my barrel, the groups opened up some jumping .010 and up.
I got no improvment by backing out of the lands from .010 in and none jamming in
more so I stuck with the .010 in.

I'm testing a new barrel with 68 gr bullets and have started at .010 in.
The powder testing is just starting but i'm getting single digit SDs and groups in the threes with H322
I will move on to seating depth testing when the wind calms down here in New England.

Gary,
You are on the right track at .010 in, at least in my experience. Carry on.
Paul

 

[Straightshooter1]

I was doing some testing on a new barrel yesterday (100) rounds. Im fairley new to this stuff so I dont know alot.

I have one load at:
Lapua brass
105 hybrids
30.2 N150
jumping .020

Second load is exact same but jumping .056

Both loads are producing acceptable groups and sd/es numbers
Is there a reason to go with one over another?

Because "jump" isn't the thing that really important here, it's better to think in terms of seating depths than jump. Whatever seating depth you have for .020 or .056 jump, keep the seating depth you choose as the jump increases due to throat erosion. If you've got a good seating depth that has a wide accuracy "node", you should be able to maintain good results as the throat erodes for quite a while.

PS: And surely don't try and compare you're jump to someone else's, as their seating depth can be very different given the same jump due to differences in chamber configuration.

 

[7x57]

I was doing some testing on a new barrel yesterday (100) rounds. Im fairley new to this stuff so I dont know alot.

I have one load at:
Lapua brass
105 hybrids
30.2 N150
jumping .020

Second load is exact same but jumping .056

Both loads are producing acceptable groups and sd/es numbers
Is there a reason to go with one over another?

then there is this:

Bullet Jump: Is Less Always Better?

About 2 years ago, Mark Gordon shared some preliminary research he’d conducted with the Applied Bal...

precisionrifleblog.com

 

[Fire Dog]

then there is this:

Bullet Jump: Is Less Always Better?

About 2 years ago, Mark Gordon shared some preliminary research he’d conducted with the Applied Bal...

precisionrifleblog.com

You beat me to it... I was going to post the same link.
A real "must read" and a quote:
At least based on this data, there seems to be evidence to suggest the Berger 105gr Hybrid may “prefer” a jump around 0.070 to 0.080”,at least that might be the most forgiving range of bullet jumps that provide consistent vertical points of impact across the variety of rifles tested.
I know someone that has found Berger 184's {7mm} going best at 100 thousand jump in his 6PRCW...
To quote Erik C "don't chase the lands..." find the seating depth that gives the most flexibility and stay with it the life of you barrel.