Jumping

[BULLET 05]

Is there a negative for finding a load that shoots good by jumping the bullets? Is there a positive for finding a load that is into the lands?

 

[rwj]

I cringe whenever a cease fire is called with a round chambered having the bullet jammed into the lands… sometimes it works out ok… often it doesn’t!

 

[Straightshooter1]

Is there a negative for finding a load that shoots good by jumping the bullets?

It really depends on how much jump you're talking about and whether the jump allows for feeding from a cartridge. Less More jump means less case volume, which could result in too high pressure to achieve a particularly high velocity. A long jump could result in other inconsistencies with a load (e.g. concentricity for uniform engraving of the bullet as it enter the bore) to exaggerate an issue. Bullets with a secant ogive are particularly sensitive to jump making them difficult to get a good tune to a load.

Is there a positive for finding a load that is into the lands?

Seating into the lands can eliminate variables for what goes on before the bullet is pushed into the lands and begins to be engraved. Along with there more consistent pressure build up and push on the bullet because of that. It tends to be more consistent than jumping. BUT . . . doing so presents the problem of having a bullet stuck in the land when the cartridge is battery and needs to be removed before firing.

 

[Link]

My best 6PPC shot best at .060 off. I never test there I found it by
''accident'' lol

 

[big5ifty]

Is there a negative for finding a load that shoots good by jumping the bullets?

No.

Is there a positive for finding a load that is into the lands?

The negative is leaving the bullet behind when you unchamber an unfired round.

 

[Fire Dog]

It really depends on how much jump you're talking about and whether the jump allows for feeding from a cartridge. Less jump means less case volume, which could result in too high pressure to achieve a particularly high velocity. A long jump could result in other inconsistencies with a load (e.g. concentricity for uniform engraving of the bullet as it enter the bore) to exaggerate an issue. Bullets with a secant ogive are particularly sensitive to jump making them difficult to get a good tune to a load.


Seating into the lands can eliminate variables for what goes on before the bullet is pushed into the lands and begins to be engraved. Along with there more consistent pressure build up and push on the bullet because of that. It tends to be more consistent than jumping. BUT . . . doing so presents the problem of having a bullet stuck in the land when the cartridge is battery and needs to be removed before firing.

Did you perhaps mean MORE jump means less case volume…?
Seating the bullet into the case reduces the volume.
LESS jump means there is more volume in the case as the bullet is further up the neck.

 

[Straightshooter1]

Did you perhaps mean MORE jump means less case volume…?

YES!

Sometimes my fingers just don't type what I'm thinking.

Seating the bullet into the case reduces the volume.
LESS jump means there is more volume in the case as the bullet is further up the neck.

Absolutely. Thanks for the heads up. I hate when that happens.

 

[BULLET 05]

I have found some pretty accurate loads on a few rifles where I am at the lands. Either at my lands number or just 2 or 3 thousands off. So now when I test a new Bullet I start with my depth same as my touching number.

 

[gunsandgunsmithing]

Depending on neck tension, but there's a long way between touch and sticking a bullet, fwiw. It doesn't have to be an absolute either/or answer. I find my best loads are typically between +/- .010 and most often, I'm somewhere between touch and sticking the bullet. Amount of jam can vary almost as much as amount of jump, depending upon bullet design and throat angle...and of course, neck tension.

 

[dthomas]

Put it where it shoots the best unless you're restricted to magazine length.

 

[drop_point]

I agree with dthomas with one caveat, a round that gets stuck in the lands and pulls apart can ruin a match. It only takes one kernal of powder behind the lugs to make your gun lose accuracy.

 

[JFrank]

I’ve run tangent ogive Bergers up to .026 off the lands and VLD ogive Vapor trails as much as .030 in the lands , I shoot the best depth after testing them.
I use the neck tension that shoots the best and holds the bullet and doesn’t soft seat.
Heavy neck tension doesn’t mean heavy seating pressure.
Interesting side note; when I do a barrel off touch point by hand, I find there’s only about a .001 difference between light stick and touch.

Jim

 

[STOMP442]

I always start my load development with a jump, usually about .025 off. I can generally find a load that shoots really well right there and rarely find a load doing a seating depth test that can beat it. I think I have one rifle that prefers to just kiss the lands.

 

[D-4297]

The part of this equation that is being forgotten ; or just plain ignored is the Chamber itself , and the amount of Freebore when the Chamber is cut , and by what type of reamer . This alone will also decide what Bullet will also be "Useable" !
A Chamber cut with a short Freebore , for lets say a Palma rifle won't allow for a 200 Hybrid , unless that bullet is seated deep in the case , possibly creating "other" problems . Just as a Chamber cut for a 215 Hybrid ; with it's "excessive Freebore won't function very well when trying to shoot a 155gr Berger .
The issue is relative when deciding what to cut your chamber , and deciding what bullets you will be using in that chamber , making that part of the discussion as important as any choice of "Jump" or "Jam" !