Bullet jump

[NHgunNut]

Just wondering how you guys detirmine your bullet jump. I have read about sizing the case lightly for low bullet tension and smoking the bullet to see where it touches. This method just seems inaccurate like i am jamming the bullet in the rifling, or my extractor is pulling the bullet to the side and rubbing off the smoke-soot. should I be making the bullet too long and letting the bolt push the bullet in the case to get my measurement?

 

[Hedge]

Hornady makes an OAL gauge for that purpose.

You need to take several measurements and take an average.

You can do what you're doing and let the bolt seat the bullet. However, I've not found that very accurate.

 

[necchi]

The tools mentioned is the ticket, it removes all doubt. You can try this;

A little squeeze of the cut holds it snug but still let's it get pushed in by the lands. Measure several times to get an average, then back off .010-.015 to be safe. Then save up too get the tools,

 

[zipollini]

The best - http://www.dolphinguncompany.co.uk/index.php?option=com_content&view=article&id=72&Itemid=93

2nd best - http://blog.sinclairintl.com/2009/03/26/determining-bullet-seating-depth/

http://blog.sinclairintl.com/2010/12/15/the-importance-of-bullet-seating-depth/

 

[NHgunNut]

Thanks for the great info guys!. being budget minded (saving up for a savage target action and 6mmBR shilen barrel) I will probably make a slit case tool. Think I will also machine up a comparator to get more accurate measurements.

 

[fdshuster]

Stoney Point (when I bought mine), now Hornady chamber O.A.L. gauge is my everyday "go to" tool for measuring both bullet seating depths, and headspace lengths. Similar excllent tool made by Sinclair also. I do like the stainless clamp-on attachements of the Sinclair over the aluminum of the S.P/ Hornady, but they are interchangable. Have & use both.

 

[Shynloco]

Just wondering how you guys detirmine your bullet jump. I have read about sizing the case lightly for low bullet tension and smoking the bullet to see where it touches. This method just seems inaccurate like i am jamming the bullet in the rifling, or my extractor is pulling the bullet to the side and rubbing off the smoke-soot. should I be making the bullet too long and letting the bolt push the bullet in the case to get my measurement?

NHgunNut,
All the posts have given great suggestions on how to measure and set your bullet. But one thing you also must consider is whether your rifle will perform with or without a jump. Since accuracy and paper shooting is my thing, I have some rifles that like a bullet setting of .001 off the lands or even touching or into the lands. But I also have a rifle that HATES having the bullets set that close and actually shoots best with the SAMMI spec in the bullet manufacturer's manual. SO don't assume you rifle will shoot better without or by reducing the "jump" because there are simply some rifles (especially general production ones vs custom built ones) that LOVE that full blown jump. Gotta test to find out which is best for your's.

 

[lloydx2]

Spit neck does work. But does require tuning. The tendency for split necks is to hold the bullet from the bottom of the neck . This can cause bullet to tip creating inacurate readings. You can take a bullet and lap this condition out. Use a well fire formed case. One that will still chamber of course. Also put a little kroil on the bullet. this will help it center in the throat. The bullet will often stick in the rifleing. Recored this reading before you put the dummy cartridge in the chamber. And if it sticks ,move back. It will take some trial and error. Good luck lloyd

 

[Nomad47]

I prefer Stoney Point (ok, Hornady) but I have done two other methods. The split case as mentioned before and I apply slight pressure with a cleaning rod to get the bullet to release from the lands as I open the bolt (amazingly consistent results). And last, a cleaning rod with a clamp (least accurate). Slide the clamp (1/4" tubing shut off valve) on the cleaning rod, insert the rod to contact the closed bolt, tighten clamp, pull rod out a few inches, insert bullet and hold into lands using the eraser end of a long pencil, push rod in to contact bullet tip, measure from muzzle to clamp.
I consider this last method to be a 'last resort'. You are measuring OAL to bullet tip instead of to bullet ogive. And it won't work on recessed muzzle barrels.

 

[necchi]

Good post Shyn,
Close doesn't ALWAYS work for more accuracy. It is talked about or made reference too by many when they describe a particular load.

I shoot off the shelf, factory guns,, these are hunters and not custom target rifles. Two of them are not even capable of of having a bullet at the lands or a jam because the freebore and chamber neck are so long some of the bullets drop out before touching the lands.
Adjusting bullets to longer than sammi has improved accuracy significantly with some loads,, but I've found concentricity to be extremely important when seating in ALL cases.

Knowing where contact is,, is still important when moving beyond sammi spec so I can safely make adjustment. but most of my best loads (Yes, even with lowly Factory Guns accuracy can be improved) are still in the .020-.030 off the lands range.

Point is, Jamming or Contact with lands isn't a golden rule for accuracy that applies to all guns.

 

[jimbo88mm]

You can use a Lee neck sizer die.. just don't size the brass all the way...

http://www.youtube.com/watch?v=kaA3GECbbVA&feature=player_embedded

 

[PREMOD70]

I use a RCBS precision micrometer with a modification to the bullet seating gauge. I use the steel spud supplied in the kit by unscrewing it from the sliding nylon insert and set the spud in a tight headspacing cartridge case measured with the headspace gauge that has been slightly sized by a Lee collet die to give the spud a sliding resistance. Place the spud in the cartridge just enough to hold it in place and then place it in the chamber and close the bolt, then removed and measure with the supplied bullet seat micrometer. The measurement can then be used for whatever bullet you choose since the micrometer is measuring at the true bullet intersection with the rifle's barrel lands. Works for me but remember to occasionally remeasure to keep up with the throat erosion.

 

[fguffey]

“Just wondering how you guys determine your bullet jump. I have read about sizing the case lightly for low bullet tension and smoking the bullet to see where it touches. This method just seems inaccurate like i am jamming the bullet in the rifling, or my extractor is pulling the bullet to the side and rubbing off the smoke-soot. should I be making the bullet too long and letting the bolt push the bullet in the case to get my measurement?”

Sizing the case neck lightly, smoking, jamming the bullet and the extractor pulling the bullet? I remove the bolt, I do not shred the neck, it is not necessary to smoke the bullet and or case and I am the fan of of all the bullet hold I can get.

I drill the flash hole/primer pocket out to a diameter that will accommodate a cleaning rod, I then size the case, after sizing the case I seat the bullet I am loading for, the COL must be short enough to prevent the bullet hitting the rifling.

After seating the bullet in the test case I remove the bolt, chamber the test case then with a cleaning rod I push the bullet out until it hits.contacts the rifling, once the bullet contacts the rifling there is no advantage in jamming the bullet further into the rifling. Once the bullet stops I remove the test case, with bullet hold it is not likely the test case will give a false reading.

Once the test case is removed it becomes a transfer, to transfer the chamber measurements to the press/seater die back the seater stem off to prevent contact with the bullet, back the die off to prevent contact with the test case then install the test case/transfer in the shell holder and raise the ram, once the ram is raised lower the seater die until it contacts the case, once contact is made back the seater die off/2 turn then secure the die to the press with the lock nut, after securing the die to the press lower the seater stem until it contacts the bullet, once the seater plug/stem contacts the bullet secure the seater stem to the die.

After the stem is secured to the die measure the height of the stem above the die, the height of the stem when measuring off the lands is .000, after measuring the height of the stem calibrate the dial caliper .000. To seat a bullet off the land .020 lower the stem .020 (then secure the stem with the lock nut). To prevent starting over when making adjustments record the stem height above the die (again then calibrate the dial caliper to .000.

Again I an not a fan of jamming the bullet against the rifling, I am a fan of the running start, I want my bullet to have a jump/running start, because? Time is a factor.

F. Guffey