How wide is a jump “sweet spot”? (6.5CR)

[EchoDeltaSierra]

Greetings all,

I’m revisiting jump on my 1700+ round 6.5CR Criterion barrel I’ve been shooting this summer. My load opened up and I decided to revisit things with some testing. Yesterday I ran 5-shot test groups (140gr ELD over 42.3gr H4350 with sub-10 ES) at 200y with .010, .020, .040, .060, .080, and .100 jumps with 34 pieces of brass left in my lot of 300. .020 was the clear winner, .080 opened way up and .100 seemed to start closing again. This afternoon, I’m headed to the long range to shoot and have 10 rounds loaded meticulously at .015, .020, and .025 to see what differences are perceived.

My question: how wide of a range (generally) is the jump sweet spot? Is that ten thousands of wiggle room, thirty thousandths, more narrow?

Just evaluating how often to track and adjust loads to stay within my desired accuracy. Thank!

 

[Supersubes]

I think it depends on your rifle/bullet combo. Use a chronograph during the eat if you have one.

 

[EchoDeltaSierra]

I think it depends on your rifle/bullet combo. Use a chronograph during the eat if you have one.

It obviously depends on that. Also, I have chronograph data since November (in Minnesota) with this new action. I know my node is good and just shot a 10 round string with a SD of 3 and an ES of 8. Only curious about the general range of tolerance for jump.

 

[Supersubes]

There’s no direct answer to your question. I think everything in the range you plan to test next will shoot fine, as it always has for me across numerous platforms. Any difference you see will likely be via the chrono, not the target.

 

[Steel head]

There’s no definitive answer for that.
Far too many variables.

 

[Jimgal62]

There’s no definitive answer for that.
Far too many variables.

Greetings all,

I’m revisiting jump on my 1700+ round 6.5CR Criterion barrel I’ve been shooting this summer. My load opened up and I decided to revisit things with some testing. Yesterday I ran 5-shot test groups (140gr ELD over 42.3gr H4350 with sub-10 ES) at 200y with .010, .020, .040, .060, .080, and .100 jumps with 34 pieces of brass left in my lot of 300. .020 was the clear winner, .080 opened way up and .100 seemed to start closing again. This afternoon, I’m headed to the long range to shoot and have 10 rounds loaded meticulously at .015, .020, and .025 to see what differences are perceived.

My question: how wide of a range (generally) is the jump sweet spot? Is that ten thousands of wiggle room, thirty thousandths, more narrow?

Just evaluating how often to track and adjust loads to stay within my desired accuracy. Thank!

Jump changes the grouping of the shots.

Once you have a node, the the groupings can collapse or expand depending on the bullet jump.

If you use 1st tier bullets, they usually perform well at 0.020”.

You run several jumps to determine when it loses the desired groupings at 100, 200 or 300 yards.

You monitor throat erosion to determine if you need to adjust seating depth to maintain your groupings.

 

[Steel head]

Jump changes the grouping of the shots.

Once you have a node, the the groupings can collapse or expand depending on the bullet jump.

If you use 1st tier bullets, they usually perform well at 0.020”.

You run several jumps to determine when it loses the desired groupings at 100, 200 or 300 yards.

You monitor throat erosion to determine if you need to adjust seating depth to maintain your groupings.

????
That’s not what I think the op is asking about

 

[EchoDeltaSierra]

Jump changes the grouping of the shots.

Once you have a node, the the groupings can collapse or expand depending on the bullet jump.

If you use 1st tier bullets, they usually perform well at 0.020”.

You run several jumps to determine when it loses the desired groupings at 100, 200 or 300 yards.

You monitor throat erosion to determine if you need to adjust seating depth to maintain your groupings.

This I have learned. Let me try to clarify my curiosity.

I have about .040" throat erosion. What was a "good load" fell apart on me. I re-ran jump tests yesterday at .010, .020, .040, .060, .080, and .100... .020" performed clearly the best.

That said, when loading lots of ammo, I like to know what the range of tolerance is for a sweet spot. As example, I know I can throw a charge at plus or minus 0.2 grains of power around 42.3 grains and still be in the node, thus there is a 0.4gr range of tolerance.

In respect to jump, if .020" shoots well, is that range of tolerance plus or minus .002" or plus or minus .010", thus giving my .004" or .020" of tolerance to work with. (these are just arbitrary numbers for example)

I hope that clarifies my first post, and again, I'm just looking for some general information to guide my personal testing.

 

[65shootmoor]

Completely depends on the bullet and rifle. SMK's, and lately, A-Tips don't seem to care at all in my rifle, but it may be different in another rifle. Only thing I would caution on is chasing perfection. You will waste a lot of ammo and risk more erosion at a point and it won't necessarily net you anything. Your rifle may have an accuracy standard from the maker or a track record you've noticed. Of course, you can chase it all you like, but I bet you won't see a substantial increase, if any, from the second test. With 1,700 down the pipe, if you are already meeting your standards or beating them, I'd stop.

 

[EchoDeltaSierra]

Completely depends on the bullet and rifle. SMK's, and lately, A-Tips don't seem to care at all in my rifle, but it may be different in another rifle. Only thing I would caution on is chasing perfection. You will waste a lot of ammo and risk more erosion at a point and it won't necessarily net you anything. Your rifle may have an accuracy standard from the maker or a track record you've noticed. Of course, you can chase it all you like, but I bet you won't see a substantial increase, if any, from the second test. With 1,700 down the pipe, if you are already meeting your standards or beating them, I'd stop.

This is a full custom and I installed the barrel myself. It was a 1/2 minute shooter and those are my expectations, but I notices it opening up around 1400 rounds. Ammo was already loaded, I didn't want to or have time to pull down bullets even though a few weeks ago I suspected things weren't as accurate as they could be. Now that I've shot through the last lot of ammo and had 34 pieces of brass left, I loaded/shot a jump test. Best group was 1/2 minute with .020" jump, the worst was .080" at just over 1.5 minutes. I know what I would choose for my match in two weeks... that said, I still will make another couple of long range trips for practice before then, and might as well gather some data while I'm at it.

Also, this is a nitride barrel, and per Criterion, we're hoping for close to 3000 rounds. And, yes, I have another matched barrel waiting to install, and a third on order.

I should know more later tonight... especially if we're shooting 800 or 1000 tonight and running the electronic targets.

 

[spife7980]

Some tangent bullets seemingly never are effected, some vlds go to crap in .005”. And of course there’s an exception to every rule.

I ran this test awhile back when I noticed my 6xc opening up at 1500 rounds and I was about done with the barrel. I did some public testing with input from hiders and this was a weight suggestion (but this powder weight is outside of my node, at 500 it goes to complete crap) but it shows how slight changes can effect things.

 

[MarinePMI]

As I understand it, bullets with a tangent ogive tend to tolerate jump better, but have a less desirable BC (hence hybrid bullet designs).

Your question is going to vary widely, since there are a wide variety of bullet forms out there for sale, even in just one weight, of one caliber.

 

[ken4570tc in WY]

Berger has a tech paper on this subject. It says it's possible to find one or more sweet spots as large as .030. Also, test out to as much as .150 from the lands. As noted above, there's no set answer for a given combination. Testing is the only way to find what your equipment and ammo will be capable of. I'm working on a Ruger Precision project, just finished primer tests and moving on to long range heavy bullet testing.

 

[EchoDeltaSierra]

Good test results last night. Checked zero and chronographed my previous best tested jump (.020”) at 100y then moved to 1000y with e-targets. .025 was clearly the best group at that distance. Shot one was expected shift and shot 8 was a flyer because of a flinch from the person next to me firing a fraction of a second before I broke the shot. The grids are .2 mil reference. I’m looking forward to running this load at the next match. Also, I want to test 10 rounds at .030 and .035, but my guess is the range of acceptable tolerance will be about .010” wide

 

[ken4570tc in WY]

Good shooting! I'm interested if anyone has tested the Berger recommendation to look for seating depth sweet spots out to .150 off the lands and what their results were? I plan on doing it after picking my preferred long range bullet.

 

[918v]

I have and it works, but it’s s rough process that still needs fine tuning.

One of my loads jumps 130 thousandths, another 100. I have some that jump 85. It all depends on the components an lot to lot variation.