The why of seating depth ?

HovisKM said:
Fishbone,

I had a stoney point tool, the problem lays in the case. Unless you fireform a case three times and then tap it your self, it is impossible for the tool to give a correct reading as the headspace will be wrong. Making a case for every barrel is just to much of a PIA to do all the time. The only measurement you are getting, without making your own cases, is from the shoulder to the lands and what you need is from the casehead to the lands. So basically, your measuring from the shoulder to lands and measuring from the casehead to lands...it just don't work without fitted cases. Chambering a round with a bullet and letting the rifling push the bullet in while it is using the casehead as a base is the only way to achieve what your wanting other than fireforming cases and tapping them. Just think about it a while.

Hovis
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Hovis,
While I agree with your above post, consider the following. Using a headspace gauge, measure the distance from the casehead to the shoulder on a case fired at least three times in your chamber; record the measurement. Now do the same with the Stoney Point or Hornady modified case. The modified unfired case will be approx. .003+ less than your fired case. Add this dimension to the measurement obtained with the SP or Hornady modified case and the measurement to the lands should be right.
 
Chino I had started another thread about the length of my brass before sizing and after.
You note .003 diff which is what I find with mine. Is that what you find to be normal?
 
I see your point, Hovis. The brass I'm using was well fire formed in my chamber before sending it to Hornady for drill/tapping. I would think that the tool should provide an accurate reading, except that it is completely dependent on zero head space. Using that same brass and a rod through the bore (attached to the brass) may be able to indicate head space. Then adding the head space value to the Hornady measurement could provide a useful number. That sounds Rube Goldbergish. I'll try clambering a dummy to engrave a bullet again.
 
Guys again this isn't rocket science, use a piece of fire formed brase with the neck tension enough to be able to hold the bullet so its not left in the chamber when you pull it out. Now with the bullet just part way in the case enough to hold it put it in the chamber and close the bolt, now instead of pulling it out and messuring it, open the bolt part way then close it again. I do this 2 to 3 times then pull it out and measure. now write down the measurement and do it three more times to make sure you get the same reading . Now you have your jam for that rifle.

Joe Salt
 
In my opinion, the only way to accurately measure one's seating depth is with using one of the comparitors that clamps to a caliper jaw. I seat a bullet in a re-sized case and push the bullet back with the seating die until I can just barely see land marks on the bullet when closing the bolt after polishing the bullet with #0000 steel wool. Measuer the OAL of the round there, measured with the comparitor on one jaw and the other jaw at the base of the case, . Record that length. This becomes one "bench mark" for determining seating depth. I call this the "Kiss". Guessing at the length of land marks is hardly an accurate way to measure, in my opinion. Most of the time, with the 30's I shoot, I find that .006 into the lands from the Kiss is where I find the best accuracy. The occasional barrel will like .009 or even .012 but most often .006" in is the best for me anyway.

Now, I realize there are lots of ways to tune a rifle but I believe If I know exactly where the bullet touches the lands, I can make my ammo as perfect as it can be made, with the tools I have to work with. We demand exact specifications with regard to the way our rifles are put together yet many seem very care-free about their ammo. I have never understood that attitude.

And yes, the throats do move forward so one should often check their kiss.
 
I spent considerable time at the bench yesterday at the start of a case prep session. I found that the case Hornady tapped for me has zero head space determined by bolt closing resistance (FP removed) and it's shoulder measurement compared to well fire formed unsized cases.
I land etched bullets to compare that method and duplicated the same reading that the Hornady rig produced.
I'm more now confident that I have a good 'just touching' reading recorded and can proceed with seating depth testing.
I plan to load 3 five round batches of depths that step up in 0.003" increments. Sound right?
Thanks for the good inputs, guys.
Ron
 
fishbone with only .003" increments, I don't think you will see much difference till you get to about 10 thou. Some rifles like more some like less. What I do is start out with at least 10 thou. after you try it in, or you will be shooting a lot of rounds that you don't need. Most rifles will either shoot touching or ten off. So if you go further and the groups keep getting tighter, go ten more at a time till it opens up. Hope you're using a chronograph. Good Luck.

Joe Salt
 
If you have the barrel off and a headspace measuring collar a sure way to get to exactly just touching is to size a case, measure to its base, seat a bullet long and measure. Move the seater by the difference of those two measurements and reseat the bullets to that setting. This will get you to the exact "just touching" position.

But remember, just touching or hard jam is just a starting reference to where the bullet actually wants to be seated for best accuracy.
 
Jerry, You got that right

JerrySharrett said:
If you have the barrel off and a headspace measuring collar a sure way to get to exactly just touching is to size a case, measure to its base, seat a bullet long and measure. Move the seater by the difference of those two measurements and reseat the bullets to that setting. This will get you to the exact "just touching" position.

But remember, just touching or hard jam is just a starting reference to where the bullet actually wants to be seated for best accuracy.
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But I have found that they often go out of tune just touching or hard jam. ( I have learned about jumping bullets) I resorted to the way we used to do it. A square mark may not be quite as good but it stays in tune better
 
Jerry Dailey said:
But I have found that they often go out of tune just touching or hard jam. ( I have learned about jumping bullets) I resorted to the way we used to do it. A square mark may not be quite as good but it stays in tune better
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Jerry D, I did not mean that just touching or hard jam is most accurate, they are just starting places. If one does not have a standard starting place they are just wandering around.

Most times somewhere between is where a barrel wants to shoot best. Tony Boyer's book gives the best description of accuracy tuning I have ever read.
 
I agree with Pete. You need to have a baseline for setting bullet depth and need to start at "Kissing". Write it down and check it again every 300 rounds. Then you can jamb or jump consistently. I have the Stony Point comparator but found it is not accurate. The Davidson seating depth checker is spot on if you use the same nose piece each time and set it in the base correctly.

And, the best way to check headspace set back is with the Redding Instant Indicator.
 
I am going against the grain on the Hornady tool advice. You do NOT want a fire formed case to be used as the one that is threaded and tapped. All that you need to do is to measure a case that is fire formed to its longest "headspace" for the particular chamber, and then measure the case and the case that is being used with the tool, and add the difference to your measurement. With a case that has not been fire formed you can come up with an accurate measurement for any chamber, as long as you have a fire formed case for it. Additionally, a case that is a tight fit may not make consistent contact at the shoulder without the leverage of the bolt to seat it in the chamber. with a loose case, there is nothing to interfere. Another thing that I have learned (from a friend) is that these tools are technique sensitive. If you are getting inconsistent results, try changing your technique. He gets very consistent results.

A related tip: To make sure that the primer of a fired case does not interfere with an accureate measurement, just use your primer tool to seat the fired primer back down below the case head. I find this handier than digging out a punch, base, and hammer.
 
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Maybe I missed it in the reading, but another good way of finding your 0.000 mark is with the Sinclair tool designed by Jon Leu when he was at Sinclair.
http://www.sinclairintl.com/.aspx/pid=35491/Product/Sinclair-Bullet-Seating-Depth-Tool
I made my own "plug" out of Delron to fit tighter.
I still use my StoneyPoint/Hornady gauge (resized, drilled/tapped case) as a rough checker. With this gauge, if I am within .004ish of the Sinclair gauge then I accept the Sinclair gauge as the correct value.
 
i just now joined this forum. been on 6mmbr for a few years and have learned a lot!! i love shooting very small hole in paper and varmint hunt, mainly northeast tenn ghogs. i am a bullet seating depth nut. i am a devoted believer in chris long's shock wave theory of rifle accuracy. his research is science and easy to comprehend. seating depth variations of as little as .005 thou. in. will alter a group's shape and location and chris explains this in terms that i can understand. powder charge changes will do the same to a lesser degree and you eventually run out of options here as pressure increases. seating depths go on forever. i am currently investigating jamming bullets and altering charges slowly to see the changes in group sizes. i know i will enjoy and learn from this forum. thanks. lpreddick
 
I bet there are at least 6 new shooters reading this, all while scratching there heads. It would seem that everyone has there own way of finding a measurement that works for them. As stated above by Jerry I think? This is just a starting point. How you find that starting point, is only really relevant, to the individual.
Jam to me, is the maximum distance, i can seat a bullet out in a fired case, with the same neck tension i intend to use for that load, before the barrel pushes the bullet back into my case. Basically What i am looking for is that longest point, or longest seating depth before the lands start to push the bullet back into the case. Again, with the same amount of neck tension, i intend to use in that load. I will repeat that practice two or three times until i am satisfied with my findings. From there i can start pushing my bullets back into my case. I usually will find a good seating depth at around .010 back from my push back length, or jam length. How was that for confusing? LOL!!! Bottom line is that, its up to the shooter to determine a system he can understand, and work with. Lee
 
skeetlee said:
I bet there are at least 6 new shooters reading this, all while scratching there heads. It would seem that everyone has there own way of finding a measurement that works for them. As stated above by Jerry I think? This is just a starting point. How you find that starting point, is only really relevant, to the individual.
Jam to me, is the maximum distance, i can seat a bullet out in a fired case, with the same neck tension i intend to use for that load, before the barrel pushes the bullet back into my case. Basically What i am looking for is that longest point, or longest seating depth before the lands start to push the bullet back into the case. Again, with the same amount of neck tension, i intend to use in that load. I will repeat that practice two or three times until i am satisfied with my findings. From there i can start pushing my bullets back into my case. I usually will find a good seating depth at around .010 back from my push back length, or jam length. How was that for confusing? LOL!!! Bottom line is that, its up to the shooter to determine a system he can understand, and work with. Lee
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And STAY WITH IT!!!. One of the biggest, most common problem new shooters have is bouncing around like a flea looking for a new meal. Develop a routine and stay with it!!!!
 
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