Too Jump...or NOT too jump?
- Thread starter broncman
- Start date
Not saying this is the rule or anything but the higher the bc or the higher the secent the more the bullet should like to jump. Its not always the case and i have seen the opposite happen a few times but that is going to depend more on your specific barrel then anything. So the VLD bullets in most of my guns like to have more jump then the non vld hunting bullets i shoot like to be jammed just a little bit. I dont like jamming unless i can't get the accuracy that i want out of the rifle. Its alot tougher on the throat and that in turn causes alot more work when trying to keep up with what the gun is wanting for seating depth. Hope this help.
bobby
bobby
spclark
Gold $$ Contributor
I don't think there's a hard and fast rule though some claim tangent ogive bullets are more forgiving while secant ogive prefer seating into the lands. As Notaguru said it depends so much on a given barrel - perhaps more specifically on the reamer profile used to cut any given chamber - it's really up to the shooter to determine what works for his particular conditions.
Up until last season I'd been shooting 6mm >100 grain bullets seated into the lands. Then I took a box of ammo loaded for another rifle to the range & proceeded to shoot better than ever... but with a different rifle! So I learned a lesson there: sometimes a jump - in this case .050" - is what works!
Up until last season I'd been shooting 6mm >100 grain bullets seated into the lands. Then I took a box of ammo loaded for another rifle to the range & proceeded to shoot better than ever... but with a different rifle! So I learned a lesson there: sometimes a jump - in this case .050" - is what works!
Hi
I set my seating depth with a felt pen marking the bullet to find the lands, found them set up to just miss.
Got realy tight groups at 100 yards very happy. ;D
Got me a Hornady comparator and digital gauge I was 0.063 away !.
Decided to move closer bad move back with the 0.063 jump using 155 gr VLD in my 308 win. :
I set my seating depth with a felt pen marking the bullet to find the lands, found them set up to just miss.
Got realy tight groups at 100 yards very happy. ;D
Got me a Hornady comparator and digital gauge I was 0.063 away !.
Decided to move closer bad move back with the 0.063 jump using 155 gr VLD in my 308 win. :
Always seated my 222 Rem. rounds for both rifles, (factory Rem. 700 BDL & Sako/Hart L46) with .020" of jump. 5 shot groups at 200 yd always average 1/2 moa or less (slightly). Two years ago was at the range, basically same weather conditions, same load, etc. and group sizes doubled, for no apparent reason. Back home compared the ammo with other's loaded for those same rifles, and found that for some reason I had seated them to touch. Seated .020" deeper, back to the range, and a return to the 1/2 moa groups. An "accident" that proved a point. 
Ken,
as others have said it's mostly the combination of bullet shoulder / nose (ogive) shape and the rifle throating. It's also affected by the bullet jacket thickness / toughness. This is one reason why most Sierra MatchKings are pretty jump-tolerant. As well as tangent form 7-calibre (or thereabouts) radius ogives, Sierras have thick jackets compared to JLKs and most Berger VLDs, so the shock of jumping 20 thou' or more then hitting the rifling doesn't faze them.
It is generally believed that secant form ogive bullets, especially if they have thin jackets need to be seated into the rifling to support and guide them. However, it's apparently not as simple as that, and Berger advises people to also try them 40 thou' off the lands as a starting point and then try 20 and 60 thou' jumps if that doesn't work as alternatives to seating into the rifling. So this sort of blows the theories about bullet damage and needing support in the throat.
Why not just seat VLDs so they're well into the lands and be done with it? Magazine feed may need a shorter COAL and this applies to some users now that the original thin-jacket Bergers are being marketed as hunting bullets. The big put-off for many competition shooters is the fear of pulling the case off a jammed bullet and leaving it in the lands if you have to unload a live round for any reason. You can soon enough knock the bullet out of the barrel with a cleaning rod, but unless you elevate the muzzle to near vertical and unload very slowly and carefully, you fill the action and locking lug areas with powder kernels - instant retiral and an onerous clean-out job off the firing line.
There was a great deal of discussion last year on the US Rifle Teams' Long-Range Shooting Forum about jumping Bergers with a lot of information from Berger Bullets' man Eric Stecker. Here's the link to the thread:
http://www.usrifleteams.com/lrforum/index.php?showtopic=10924
Personally, I think the new breed of stretched nose tangent designs is the way forward for target shooting - as good BCs as VLDs, better in some cases, and easy to tune in most loads. German Salazar is a fan of the 175gn Berger match BT in .308W Palma type rifles, and I've found the 185gn Berger Match BT Long-Range an exceptional bullet in this cartridge in F/TR and plan to try the 210gn version too alongside VLDs in the 175-210gn range.
Berger is currently introducing such designs in other calibres too such as the 108gn 6mm. I seem to remember seeing somewhere that there is a new 105gn Long-Range tangent model in the pipeline as well. The company says it intends to offer alternatives of high-BC tangent ogive and VLD secant ogive models in heavy long-range form in every calibre.
Laurie,
York, England
as others have said it's mostly the combination of bullet shoulder / nose (ogive) shape and the rifle throating. It's also affected by the bullet jacket thickness / toughness. This is one reason why most Sierra MatchKings are pretty jump-tolerant. As well as tangent form 7-calibre (or thereabouts) radius ogives, Sierras have thick jackets compared to JLKs and most Berger VLDs, so the shock of jumping 20 thou' or more then hitting the rifling doesn't faze them.
It is generally believed that secant form ogive bullets, especially if they have thin jackets need to be seated into the rifling to support and guide them. However, it's apparently not as simple as that, and Berger advises people to also try them 40 thou' off the lands as a starting point and then try 20 and 60 thou' jumps if that doesn't work as alternatives to seating into the rifling. So this sort of blows the theories about bullet damage and needing support in the throat.
Why not just seat VLDs so they're well into the lands and be done with it? Magazine feed may need a shorter COAL and this applies to some users now that the original thin-jacket Bergers are being marketed as hunting bullets. The big put-off for many competition shooters is the fear of pulling the case off a jammed bullet and leaving it in the lands if you have to unload a live round for any reason. You can soon enough knock the bullet out of the barrel with a cleaning rod, but unless you elevate the muzzle to near vertical and unload very slowly and carefully, you fill the action and locking lug areas with powder kernels - instant retiral and an onerous clean-out job off the firing line.
There was a great deal of discussion last year on the US Rifle Teams' Long-Range Shooting Forum about jumping Bergers with a lot of information from Berger Bullets' man Eric Stecker. Here's the link to the thread:
http://www.usrifleteams.com/lrforum/index.php?showtopic=10924
Personally, I think the new breed of stretched nose tangent designs is the way forward for target shooting - as good BCs as VLDs, better in some cases, and easy to tune in most loads. German Salazar is a fan of the 175gn Berger match BT in .308W Palma type rifles, and I've found the 185gn Berger Match BT Long-Range an exceptional bullet in this cartridge in F/TR and plan to try the 210gn version too alongside VLDs in the 175-210gn range.
Berger is currently introducing such designs in other calibres too such as the 108gn 6mm. I seem to remember seeing somewhere that there is a new 105gn Long-Range tangent model in the pipeline as well. The company says it intends to offer alternatives of high-BC tangent ogive and VLD secant ogive models in heavy long-range form in every calibre.
Laurie,
York, England
yes i have had good luck with jumping bergers over .08" even as much as .125". Only the VLD's though. I have not found many non VLD's that like to jump that much but the nosler bal-tips will like that sometimes as well. I wish there was some kind of formula to tell me what to do though. It can get rough.
Thanks guys for all the replys! Reason I am asking is I have a Sako A& in 7-08 that has a horrendously long throat. Can't get no where near the lands at max magazine length. Getting some fliers and was thinking length. Hornady's, Accubonds, Combined Tecnologies all will have a flier and I have been over everything from technique to equioment.
The "science" behind it the jump and behind accuracy is the main reason I asked though. If I win the lottery, I would build a lab. I like to know why?
I had not given jacket distortion as much thought as I had bearing surface differences between the ogive designs. I also wondered about the bullets center of gravity in relationship to length having an effect on long jumps and the push from the gas pressure?
Ken
The "science" behind it the jump and behind accuracy is the main reason I asked though. If I win the lottery, I would build a lab. I like to know why?
I had not given jacket distortion as much thought as I had bearing surface differences between the ogive designs. I also wondered about the bullets center of gravity in relationship to length having an effect on long jumps and the push from the gas pressure?
Ken
Thats just a tough place. Best thing for you to do is get a few different types of bullets and try them until you find the one that likes to jump in your rifle. Other then loading them out and single feeding them when you need the extra accuracy there is not really much you can do. Maybe get the chamber set back a little bit with less freebore.
If life was simple, then there would be no challenge in reloading... and we would have no information to swop!
I have been running Berger 88gr in my 9 twist 6x47 Lapua with great results (15 thou jump and 41gr of RL17). However, at Bisley a few w/ends back I fired my first two shots using the last of an old batch (each hitting the ball 800 yards) and then moved to a fresh batch of reloads.
In reloading the second batch I had somehow moved from having a 15 thou jump, to being just in the lands. The difference was remarkable... firstly the point of impact climbed 20", reflecting something like a 200 rise in fps and the brasses showed the start of pressure signs.
When I got home and reseated them to the original 15 thou jump, the problems and pressure signs moved away.
I have no conclusion to offer, only observations.
I have been running Berger 88gr in my 9 twist 6x47 Lapua with great results (15 thou jump and 41gr of RL17). However, at Bisley a few w/ends back I fired my first two shots using the last of an old batch (each hitting the ball 800 yards) and then moved to a fresh batch of reloads.
In reloading the second batch I had somehow moved from having a 15 thou jump, to being just in the lands. The difference was remarkable... firstly the point of impact climbed 20", reflecting something like a 200 rise in fps and the brasses showed the start of pressure signs.
When I got home and reseated them to the original 15 thou jump, the problems and pressure signs moved away.
I have no conclusion to offer, only observations.
My barrelsmith tells me that throat angle has a lot to do with bullet seating depth. For instance in .223 reamers, the throat angle varies from 1.2 to 3.1 degress. In general, seat kissing for smaller angles and away for larger angles. But as has been stated, barrels vary in preference. My 6AI and .223 are kissing the lands with AMax moly bullets (thin jacket) and my .308 is .020 off with 155 SMKs (thick jacket).
I casually mentioned this to a fellow F Class shooter during a lunch break at a 1000 yd practise last Summer. Suddenly I was confronted with deep indignation, his eyeballs bulging and pointing in two different directions, stating that throat angle doesn`t have anything to do with seating depth. He wondered why I was even allowed on a rifle range with such deficient knowledge. He was near last in the 3 day Agg at the 2009 Ontarios. I was in a shoot-off for the 1000 yd title. Felt like asking him how his throat angle was doing but left it alone.
Here is a link to .223 reamers. Throat angle is at the bottom. http://www.ar15barrels.com/data/223-556.pdf
I casually mentioned this to a fellow F Class shooter during a lunch break at a 1000 yd practise last Summer. Suddenly I was confronted with deep indignation, his eyeballs bulging and pointing in two different directions, stating that throat angle doesn`t have anything to do with seating depth. He wondered why I was even allowed on a rifle range with such deficient knowledge. He was near last in the 3 day Agg at the 2009 Ontarios. I was in a shoot-off for the 1000 yd title. Felt like asking him how his throat angle was doing but left it alone.
Here is a link to .223 reamers. Throat angle is at the bottom. http://www.ar15barrels.com/data/223-556.pdf
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