Is jump to lands or bullet in neck depth more important?


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GJgo
October 15, 2011, 08:37 PM
I've run into a new dilemma while loading for my 6.5 Swede. It's a Win 70, long throat. I'm trying a load with 140 Amax. I can load them .015" off the lands, and they shoot well with low ES, however there's only about .150" bullet engagement in the neck. (Neck tension is about .0015".) In order to get full neck-to-bullet engagement I'd have to set the bullet about .175" off the lands.

First I thought I needed more engagement for whatever reason, but like I said the velocity spreads were pretty low with the minimal engagement. I torqued on a bullet with my fingers and it isn't going anywhere... What do you guys think is more important?

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Walkalong
October 15, 2011, 09:41 PM
Which ever way your rifle shoots best.

I have a .222 Mag that shoots bug holes with the bullets barely seated, but close to the lands.

This does not always work, and as usual, there are many other variables to consider.

rcmodel
October 16, 2011, 12:08 PM
Something to ponder perhaps?

Factory Match ammo isn't loaded to the lands.

rc

GJgo
October 16, 2011, 08:31 PM
That would depend on the free bore in the particular rifle, don't you think? For example, Federal GMM 175 SMK is loaded such that it's a couple thou into the lands in my Savage 10FP. If I loaded to the OAL in my Sierra book it's also be just into the lands.

At any rate I think I've found my own answer. At the .015" jump as described above I found two loads today (H4831SC & H1000) that put a 3 shot group right around an inch @ 200 yds. Plenty good enough for a deer rifle so I'm going with that. :)

Walkalong
October 16, 2011, 08:36 PM
Well there you go, but I wonder what it might have done seated shorter. Did you try it as well?

sage5907
October 16, 2011, 08:57 PM
Just as a general rule for reloading a high powered rifle you should have the diameter of the bullet inside the case neck. For a .264 diameter bullet you should have at least a length of .264 of the full bullet diameter inside the case neck. That may not be important while shooting at the range but shooting in a hunting situation could be different. In a rifle with recoil the recoil could cause bullets in the magazine that are seated to only .150 to move forward in the case neck. When chambered they could stick in the lands and remain in the lands when the loaded case is ejected. Weird things happen when hunting so I would seat the bullet at least .264 in the case neck. That's only .064 further into the case neck for a hunting round. BW

GJgo
October 16, 2011, 08:59 PM
I did try a ladder test at .100" jump but I didn't shoot groups. There was a pretty clear node however it took 2 more grains of 4831 to reach the same velocity.

One concern I had about a long jump is what if it makes bullet runout more of a problem? The way my die is clocked now I'm getting between .002-.004" runout.

I'm actually starting to think that jump & powder charge have criss-crossing nodes, kind of like how increasing altitude mirrors increasing latitude. IOW you're really just looking for the correct velocity that your setup likes & there are many combinations that will acheive it.

ranger335v
October 16, 2011, 09:27 PM
"Is jump to lands or bullet in neck depth more important? "

Aren't they directly related? Increasing one increases the other!

amlevin
October 19, 2011, 11:47 AM
I've found that the rifle will give you the answer. I tried following all the suggestions of "just off the lands" with my rifle. Shot OK but when I went back to a length that would reliably feed from the magazine it shot GREAT. The shorter round had a huge jump to the lands but the groups could all less than 1/2MOA @ 300 yards.

Again, the rifle will yield the answer.

FWIW, I watched one shooter at the range jamb his bullet into the lands first and then loaded a case loaded only with powder and a green plastic foam that's used by florists. One-hole groups all day long for him. Not only no zero jump, but zero neck tension and bullet insertion in the case.

Red Cent
October 19, 2011, 03:06 PM
Amlevin, without experience this could cause some problems.

On the other hand, Weatherby rifles chambered for their proprietary cartridges all have considerable freebore.

Remington 700s are noted for a little freebore.

Unless you are benchresting, most times there will be little difference in accuracy.

With 1/2moa at 300 yards, stop. :)

GJgo
November 29, 2011, 08:20 PM
Does anyone have a feel for how much jump is too much? I was thinking of trying some 120 TSX or TTSX in my Swede, but to get any neck tension I'm guessing I'd be jumping around .300" or more, and for $35 for 50 I hate to buy a box & find out it's no good...

twofifty
November 29, 2011, 08:58 PM
Cast your chamber then measure how much room there is for the neck, leade and where the lands start.

There may well be enough room to allow case necks to run a bit on the long side of SAAMI specs; they'll grow with each firing/resizing cycle. This will gradually allow you to increase the effective seated depth of your bullets, while maintaining that short jump your rifle likes. If you measure accurately and only trim cases minimally and as absolutely required, you can maintain safe pressures. But you gotta keep track of things and monitor case length each time.

These long-necked cases and long COL rounds would most likely be dangerous in any other rifle - the long necks would impede bullet release on ignition.

T Bran
November 29, 2011, 09:17 PM
GJgo
you mat be ok with a longer seating legnth with the Barnes since they are solid copper they make up the difference in legnth. In other words a 130 grain Barnes is longer than a typical cup and core style bullet.
T

30Cal
November 30, 2011, 05:43 PM
I wouldn't go much less than one dia. in the neck. Especially in a hunting rifle.

Walkalong
December 1, 2011, 07:41 AM
I agree. I do not worry about jump to the lands in hunting rifles.

RentaCop
December 1, 2011, 08:06 AM
I wouldn't go much less than one dia. in the neck. Especially in a hunting rifle.

+1 to dat

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