Jump to the lands

[jacq220]

working up a load for a new rifle. i made a dummy round that is 2.215 COAL measured off the ogive.

when i loaded up the first 5 rounds 155 scenar over 44 grains of varget (.308) my cases measured 2.150 to the ogive.

is .1 to much of a jump. as i understand most people go a few thousands off the lands, this is a tenth of an inch... is this to much? coal w/out going to the lands is 2.775 per the manual. should i seat the rest of them out further?

note, the dummy round i made is 2.865 w/out measuring off the ogive and WILL fit in the mag.

lets figure this out before i load up the rest of the test rounds.

 

[fx77]

Re: Jump to the lands

10 thousandths is not at all to close.
Common technique to workup a load is to close the bolt on a dummy round and note the length to ogive when the land marks on the bullet are equally wide and long commonly called the "Jam"

One frequently then shoots various charges of powder loads to get best accuracy group of 5 avoiding XS pressure signs.

Then can try shortening the length to the ogive a couple of thousandths at a time until your group gets better or is unchanged. Some barrel bullet combos like a jump and some like starting jammed into the lands.

This assumes that the round is not too long for, should U be suing one, a magazine (jam length) in which case your max length is guided by the fit to the magzine.

 

[MALLARD]

Re: Jump to the lands

+1 fx
let me get this straight , you measured your ogive contact with the lands at 2.215 ? and your loading them at 2.150 , so your your now .065 behind the lands ?

thats not to bad , most reloaders will get the bullet much closer , but i have heard of some guns shooting well with bullets seated that deep.

but , .06 is allot , .02-.03 is more normal , allot of guys will be .010 - .005 off , some reloaders even seat their bullets so they will get stuck in the lands so that if you try and extract that loaded round you will make a powder mess , i think its called dead length seating , or something.

when you say to much , do you mean dangerous ? no , probably not. IF you mean to much in terms of accuracy , maybe , maybe not.

 

[schwim]

Re: Jump to the lands

Looks like he's asking about 100 thousandths. How did u make up the first dummy round? Do u have your actual chamber oal measured with that bullet?

 

[Nortex]

Re: Jump to the lands

If you know your OAL why did you load your rounds with such a jump in the first place? I personally load mine out to .005 off the lands then start from there.

 

[vman]

Re: Jump to the lands

0.1" is a big jump imo.

I know the scenars are long, but they shoot better closer from my experience. The last 1000 scenars that I have shot have been kissing the lands and I have seen the best accuracy in my rifle with this combo.

 

[Clark]

Re: Jump to the lands

I get the bullet into the lands half way from touching threshold to getting stuck threshold.

Lots of people have been competitive at Camp Perry, but what makes Bart Bobbitt special is how well he writes about it:

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body">Bart Bobbitt 2003:
The most accurate centerfire rifles typically do best with bullets
seated out a bit so they contact the lands and push back a few
thousandths into the case. This makes the starting resistance more
uniform from shot to shot as well as centering the bullet in the bore
before its fired. However, if ease of removing a loaded round from
the chamber, I'd seat bullets out to within only a couple thousandths
from land contact which centers the bullet pretty good. The more a
bullet is seated off the lands, the less it will be centered in the
bore before firing.

To set up for a bullet's contact seat, the case neck has to be sized
such that there's not much tension on the bullet. One problem that
sometimes happens is that the neck grips the bullet tight enough to
jam it into the lands fairly tight and if the round has to be removed,
the bullet stays in the barrel and powder infiltrates your action.
The solution is to find out what neck tension is right for your
rifle's chambering, then use it.

Using a slightly larger expander ball or lapping out the die's neck so
you don't need an expander ball is a good way. But it takes measuring
and metal working skills to do it; a decent 'smith should be able to
do this for you if you can't.</div></div>
http://groups.google.com/group/rec.guns/...71ca836132b1245

 

[Lobo Widowmaker]

Re: Jump to the lands

I generally set OAL 0.020" - 0.035" off the lands. Use the Hornady Lock'N'Load tool.

 

[jacq220]

Re: Jump to the lands

I got the OAL by jamming a dummy round in and tapped it out w/ a rod... i have the hornady tool, but lost the .308 casing, and my taps and dies are at the shop which i wont be back to til next week.

i loaded that far back because i was following the manual... ill seat them a bit further out...

i was sub moa accross the board w/ these loaded this way and 46 46.5 and 47 grains of varget all showed promis... shooting from 46-47 in .2 grain increments on saturday, then ill play w/ seating depth a bit.

 

[rymart]

Re: Jump to the lands

Depends on the bullets. When I jump them, I preferr 0.010 - 0.025. I never use the book recommended OAL's, but measure instead. I've heard of Weatherby's shooting well with enough freebore to jump further than that... but I've never seen a weatherby that shot well... could just be a rumor.

 

[vman]

Re: Jump to the lands

Clark, that is well said... i like when people state their reasoning.

Im not too sure about lapping dies and all of that... it seems a little much if you ask me. But each to their own I guess.

I put myself in that tactical rifle shooter category, so i think this is less of an issue for me.

 

[krw]

Re: Jump to the lands

Lots of factory Remington rifles have at least .100" freebore. There is no way to load mag length and be anywhere near the lands. A buddy of mine who has a 7mmSTW, His rifle has .165" freebore. Its factory Rem. This is why a custom rifle that you can spec the freebore is so nice.