Don't be afraid to "jump" !

[jamesdmock]

Normally, I am not a big fan of jumping bullets, but one may find good accuracy by trying it. I have a 6mm BRA barrel that I thought was ready to be retired. It shot pretty good with Bart's Gungnirs seated +.005 into the lands and loaded with 30.6 grains of H4895 or 30.4 of 8208 XBR. (when it was new). Lately, I tried some of the same Gungnirs with increasing the jump in a test. I started with -.005, then .015, and .025. When I got to .025 jump, the old barrel seemed to come alive. It now has 1060 rounds and I plan to shoot it in a 600 yard match this Saturday. Yesterday, I checked my 600 yard zero and shot a 0.960 3-shot group at that distance. I may have a train wreck Saturday, but this load of 30.4 grains of H4895 will not be the cause. Good shooting.....James

 

[PatMiles]

Hope not!

 

[jackieschmidt]

I jump my 30 BR about .020. My 6BR shooting the 80 grn Bart’s likes about a .020 jump as well. The 65 Grn Bart’s Boat Tail in my 6PPC’s like even a little more than that.


Thr only bullet I “jam” now Is the Bart’s Ultra and Headhunter.

 

[shoot4fun]

Van Halen has been telling you that for years!
Van Halen - Jump (Official Music Video) - YouTube

 

[foxguy]

I jump my 30 BR about .020. My 6BR shooting the 80 grn Bart’s likes about a .020 jump as well. The 65 Grn Bart’s Boat Tail in my 6PPC’s like even a little more than that.


The only bullet I “jam” now Is the Bart’s Ultra and Headhunter.

What Powder are you using in the the 6MM BR with the 80 gr Barts?

 

[shoot4fun]

I was under the impression Gungnirs were a VLD profile bullet with a little different ogive. Berger has long said test VLDs off and that they have had them shoot extremely well as far as 50 thou off the lands.

 

[K22]

I've found this to be true in many factory rifles I've owned over the years; some indeed to better with more jump. Whether this is due to less run out because the bullet is seated deeper, greater neck tension via more contact, higher pressure, or some other reason I don't know.

Sierra published an article many years ago about this very subject noting that some rifle shoot better with more jump.

With Remington 700's (at least the vintages I own) you have no choice but to accept a long of jump due to the long free bore. I found no difficult at all in developing very precise loads in these rifles with the long jump.

Most factory ammo have the bullets are seated quite deep and I've seen some amazing groups shot at the range with factory ammo. Just a few weeks ago I witnessed a guy shoot a sub 1/2", 5 shot group with Federal 6.5 Creedmore ammo in a factory Savage Long Range Hunter model rifle.

 

[swimster]

I did a seating depth test at 500y with 2 different rifles. 1 was a 22 Brx shooting 75g Elds the other was a 22/250 Ai with 88g Elds . I was just looking for vertical dispersion. Both bullets seemed to have 2 nodes at about the same distance off the lands. 1st node was about 20th wide between. 005 to 25 th. The second was from .035 to.060. Vertical impact of both nodes were within 2 3/4 inch vertical. Just one trip out need to do a follow up to verify.

 

[RegionRat]

https://precisionrifleblog.com/2020/04/28/bullet-jump-research-and-load-development-tips/

A little nightstand reading for you on jump that just goes to show there isn't anything really new under the sun....

 

[swimster]

That's the article I read. Thought I would give it a try.

 

[INTJ]

To paste a quote from the article:

"What if instead of looking for the one exact bullet jump that provides 100% optimal precision and having to constantly adjust the seating depth as the lands of the barrel erodes, we instead looked for the bullet jump that is very forgiving AND still provided good precision over a wider range of jumps?"

The answer is if you choose do that, you will place poorly if you shoot BR. That might work for PRS, but not for a high accuracy discipline.

 

[dgeesaman]

Just a few weeks ago I witnessed a guy shoot a sub 1/2", 5 shot group with Federal 6.5 Creedmore ammo in a factory Savage Long Range Hunter model rifle.

That’s because Creedmoor

 

[jackieschmidt]

What Powder are you using in the the 6MM BR with the 80 gr Barts?

Accurate 2495. The best Load I have found for accuracy and SD is 33.5 grns.

 

[dnellans]

To paste a quote from the article:

"What if instead of looking for the one exact bullet jump that provides 100% optimal precision and having to constantly adjust the seating depth as the lands of the barrel erodes, we instead looked for the bullet jump that is very forgiving AND still provided good precision over a wider range of jumps?"

The answer is if you choose do that, you will place poorly if you shoot BR. That might work for PRS, but not for a high accuracy discipline.

IMHO that article grossly misstates what they actually tried to study. They talk about it as if they’re measuring average precision over a range of jumps. However they’re actually measuring the vertical average displacement of three shot groups. It provides no data on actual group sizes being shot, just where there are centered with no horizontal component even considered.

The conclusion that I believe you -could- actually reach from their data is that you should expect a ~.8 moa vertical shift in your zero over 200-300 rounds due to throat erosion if you use a “small” jump.

However if my zero shifted that far over the course of a 2 day match I would be missing most targets on day 2 even though we shoot at bigger targets than other disciplines.

My personal experience has been that if I check zero after a match (usually looking for a reason I sucked), it’s within a .1mil click which is range of adjustment on most of our scopes. If I get off and back on the gun between all groups, the center of my groups will also wander far more than if I shoot them all back to back. With as many guns, days, shooters they have, I suspect that is a lot of noise in their data.

Would be interested to hear @Sheldon N ’s experience as a PRS shooter and analytical guy.

 

[shoot4fun]

That’s because Creedmoor

Guess you don't know the reputation of those Savage rifles. They ALL shoot 1/4" groups all day long even when he shooter doesn't do their part!
That Creedmoor didn't have a chance to miss.

 

[Sheldon N]

IMHO that article grossly misstates what they actually tried to study. They talk about it as if they’re measuring average precision over a range of jumps. However they’re actually measuring the vertical average displacement of three shot groups. It provides no data on actual group sizes being shot, just where there are centered with no horizontal component even considered.

The conclusion that I believe you -could- actually reach from their data is that you should expect a ~.8 moa vertical shift in your zero over 200-300 rounds due to throat erosion if you use a “small” jump.

However if my zero shifted that far over the course of a 2 day match I would be missing most targets on day 2 even though we shoot at bigger targets than other disciplines.

My personal experience has been that if I check zero after a match (usually looking for a reason I sucked), it’s within a .1mil click which is range of adjustment on most of our scopes. If I get off and back on the gun between all groups, the center of my groups will also wander far more than if I shoot them all back to back. With as many guns, days, shooters they have, I suspect that is a lot of noise in their data.

Would be interested to hear @Sheldon N ’s experience as a PRS shooter and analytical guy.

They've got my interest in exploring longer jumps, but I haven't done it yet. Probably on the next barrel. I do know that I've heard things from other shooters that make me think there's something there, not for ultimate accuracy but rather for load forgiveness which is important for PRS game with 250 rounds in two days and no cleaning of the barrel.

A flaw with the article is that is assumes that changing your seating depth from 0.020 off to 0.050 off on a new barrel is the same as choosing a load at 0.020 off and shooting it until it erodes to 0.050 jump. I don't think that's necessarily going to be equivalent.

As far as the vertical displacement difference at distance, I suspect that it's not a zero shift but rather a combination of velocity change or barrel harmonics as to the timing of when the bullet leaves the barrel. There's a start-stop-start that happens when the bullet encounters the lands and changing variables can change the timing of it all. My guess is that longer jumps mitigate the sensitivity of that timing to changes, and that's where the load forgiveness comes in to play.

 

[2506]

I discovered the long jump with Berger VLD long before Berger started telling people to try it. The norm back then was right up to or into the lands. I had a rifle that had a looooog throat. I wanted to shoot out of the magazine but when I loaded up to the lands they were too long for the magazine. I tried some at magazine length which was a mile off the lands and BUG HOLES. I had already discovered that Sierra MK like to jump a good ways as well as other "hunting" bullets. Been hand loading 40 years.

 

[dogdude]

In '09, shooting a Dasher with Sierra 107's..60 off.took second place L/G group @ the IBS Nat's (Iowa)
Today my 300 WSM, shoots nice @ .081 off ,210 Matrix.

 

[INTJ]

IMHO that article grossly misstates what they actually tried to study. They talk about it as if they’re measuring average precision over a range of jumps. However they’re actually measuring the vertical average displacement of three shot groups. It provides no data on actual group sizes being shot, just where there are centered with no horizontal component even considered.

The conclusion that I believe you -could- actually reach from their data is that you should expect a ~.8 moa vertical shift in your zero over 200-300 rounds due to throat erosion if you use a “small” jump.

However if my zero shifted that far over the course of a 2 day match I would be missing most targets on day 2 even though we shoot at bigger targets than other disciplines.

My personal experience has been that if I check zero after a match (usually looking for a reason I sucked), it’s within a .1mil click which is range of adjustment on most of our scopes. If I get off and back on the gun between all groups, the center of my groups will also wander far more than if I shoot them all back to back. With as many guns, days, shooters they have, I suspect that is a lot of noise in their data.

Would be interested to hear @Sheldon N ’s experience as a PRS shooter and analytical guy.

A .8 MOA shift would be bad for most any shooting discipline.

Many of us have known for a very long time that the closer the bullet is to the lands, the more sensitive it is to changes in seating depth. To that end I like it when I find a node that is well off the lands. I don't worry about going out of tune during a 2-Day LR BR match.

With a hunting rifle I start .020 or more off the lands and don't even check seating depths close to the lands since I want a reasonably accurate load over a wide range of conditions.

However, many times the best accuracy node is small and close to the lands. In many competitions, a .1 MOA improvement is worth taking the the fussier node and it is absolutely not a big deal to chase seating depth.

 

[dnellans]

They've got my interest in exploring longer jumps, but I haven't done it yet. Probably on the next barrel. I do know that I've heard things from other shooters that make me think there's something there, not for ultimate accuracy but rather for load forgiveness which is important for PRS game with 250 rounds in two days and no cleaning of the barrel.

A flaw with the article is that is assumes that changing your seating depth from 0.020 off to 0.050 off on a new barrel is the same as choosing a load at 0.020 off and shooting it until it erodes to 0.050 jump. I don't think that's necessarily going to be equivalent.

As far as the vertical displacement difference at distance, I suspect that it's not a zero shift but rather a combination of velocity change or barrel harmonics as to the timing of when the bullet leaves the barrel. There's a start-stop-start that happens when the bullet encounters the lands and changing variables can change the timing of it all. My guess is that longer jumps mitigate the sensitivity of that timing to changes, and that's where the load forgiveness comes in to play.

I was comparing to a "zero shift", because you're gonna zero at the start of the match for whatever load you've got. Unless something goes really off the rails, you aren't changing it over the course of the match. So be it velocity, harmonics, or whatever else, that is causing consistent impacts low or high of your zero (and assuming you're doped right to start), that would sort of look like a zero shift over the course of the day. If you don't think of it that way, then you would be stuck wondering if your dope is wrong suddenly.

I could easily believe that a large jump smooths out the pressure spike when the charge ignites though, just as we all know that seating "at touch" can be well, touchy, if you're not consistently on or off them. I agree with Sheldon that the bullet starting at same depth and differing jump via erosion isn't the same as just changing your seating depth where internal volume of case is going to change some. that said, i've tried to do some systematic testing before and i haven't noticed seating depth make a huge difference on SD/ES, but it does change group sizes. so maybe its more about a harmonics thing than pressure anyways.