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Discussion in 'General Firearm Discussion' started by Sabertooth, Dec 21, 2014.
How far is the bullet jump in your rifle???
You mean how much space befor the bullet makes contact with the lands....?
That will vary unless you load your own match ammo and then best accuracy is for the bullet to just touch the lands when chambered. No "jump" Factory loads not so much. They all vary. Usually a few thousandths to maybe .050, but even that varies a bunch.
If you hand load, make a dummy round and smoke the bullet or even use Prussian blue and then set your seating die to just barely see the marks left on the bullet where the lands touch. You could even set it a couple thousandths deeper and lock it in. As with any changes, work up your loads every time you change anything.
I would seat a little more if just making hunting loads, but this will make a big difference in match ammunition.
.308Win Krico with Scenars - 0.005"
.308Win Schulz & Larsen - same bullet - 0.020"
7.5x55 K31 and K11 - touching the lands in the K31 and the same COL for the K11
7x57 Mauser from 1912 - just touching with 175gr.
7x57 Mauser carbine Boer War bringback - 0.045" - no round-nosed bullets here in UK, so I used the same COL as the rifle above.
6.5x55SE m/96 - touching, just.
.45-70 Winchester High Wall - flat-nosed or round-nosed - 0.0050".
None. But then my bullets don't scare easily.
The jump into the throat can be adjusted with a reamer to reduce recoil on large caliber rifles.
It cant really be adjusted. It can be lengthened. But not shortened.
But I know what your saying.
I believe the term is "leade" that distance behind the groove which is theromagically apportioned to that point where your Chamber is reamed to your Caliber...
When I read the title, I could not help but recall the comedy Westerns where a Cowboy would entertain the watcher of said movie, by saying "Dance" and bullets would ~jump~ around some feet...
I'm thinking ''free bore''. A smooth area without rifling's the bullet goes through before it engages the rifling's.
This keeps pressure down. And like Just Jim said helps with recoil.
I know my friend Mike shoots a 300 Weatherby. And its got a 1/2 free bore area before the rifling starts.
Of course little bullets, dancing for there lives! Could be what were talking about?
Ya need the P.O Ackley Books
Here is a great tool for accurate seating depth. Micrometer seating die.
All calibers and bullets react differently to changes in everything that influences it.
Work all loads up with good record keeping and read and learn
from every source you can find. You can go to extremes when loading for accuracy. Batch numbers of bullets, brass, primers, powders are all important and when one of them changes, the entire load needs to be worked up again.
Case weight, neck thickness, length, Bullet weight consistency, spin for concentricity using a precision collet and holder/spinner and dial indicator in .oo1, but .0001 even better. SOOOOO many things influence accuracy before the cartridge even gets into the firearm then a whole new set of conditions develop.
Barrel length, twist, bedding vs free floating, type of crown and on and on and on and on.
If you want ultimate accuracy, the tasks and to-do's can occupy your time 24-7/365 LOL
I became obsessed with accuracy and went overboard for many years
Accuracy knows no limits.
https://www.google.com/search?q=ackley bullet seating depth for accuracy&num=100&lr=&biw=1366&bih=579&source=lnms&tbm=isch&sa=X&ei=4b2YVPidA8rgoAS684KIBA&ved=0CAgQ_AUoAw#tbm=isch&q=bullet concentricity&imgdii=_
https://www.google.com/search?q=ackley bullet seating depth for accuracy&num=100&lr=&biw=1366&bih=579&source=lnms&tbm=isch&sa=X&ei=4b2YVPidA8rgoAS684KIBA&ved=0CAgQ_AUoAw#tbm=isch&q=case neck thickness bullet concentricity&imgdii=_
No it does not end. Then you can build your own measuring fixtures and jigs on top of the rest.
When you have reached the point of breaking/cutting single kernels of powder to get that perfect load, you know you officially have a real live obsession <ROFLOL>
That goal of 10 in the same hole at multiple ranges never goes away Taking the head off a running Jack at 200 yds became an obsession also. We would never shoot a sitting jack rabbit. Always challenge yourself to the max. It only makes you better.
That little item of lead, jump, etc; is just one of dozens of things to think about.........
Its good that you are though.
Sorry... too much information for the question asked.. I must still be obsessed. LOL
Funny part is I quit reloading and sold everything :/