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bullet seating accuracy

 
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  #1  
Old 08-23-2013, 03:16 PM
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Join Date: Aug 2013
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bullet seating accuracy

I am kind of new to reloading. I used to use a lee classic handloader but now have a press. With the handloader it was very time consuming to get perfect seat depths, not just because bullets are man made objects and therefore are not 100% uniform, but also the fact I was using a mallet to seat it.
But even with the press and the die set tight I still manage to under seat or over seat and have to constantly "baby" the depth into place. How do you more experienced loaders get the depth perfect without growing older trying?
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  #2  
Old 08-23-2013, 03:47 PM
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Re: bullet seating accuracy

How are you measuring/defining your "depth"?
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  #3  
Old 08-23-2013, 05:15 PM
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Re: bullet seating accuracy

I use a hornaday digital caliper and look for overall cartridge length off the lands.
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Old 08-23-2013, 05:56 PM
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Re: bullet seating accuracy

if you are useing the same bullet (and this can change from one lot number to another) than after you set your depth on your seat die you should be good to go.
I use the Lee positive seat system it has no ability to crimp and the die is screwed all the way down to the shell holder. When locked in place all of my bullets are the same over all length
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  #5  
Old 08-23-2013, 07:59 PM
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Re: bullet seating accuracy

If you're using COAL to determine how far off the lands you are, you wont be able to that accurately with cup and core bullets. Cup and core bullets have variation in their shape from bullet to bullet. If you get your calipers and measure the OALs of the bullets, you will see they vary in length. They also vary in bearing surfaces, ogive, etc. I just measured 10 230 Berger hybrids and their OAL differed by as much as .012. I put them nose first into a sized case (this is approximately where the ogive engages the lands) and measure from the case head to the base of the bullet and that varied up to .008 A bullet comparator does the same thing.

If you want to seat accurately and consistently "off the lands", then you need to use a bullet comparator and measure the seated ogive length of every round you seat and use a micrometer seating die to adjust for the differences. Some will also sort their bullets according to bearing surface as well. That's a lot of effort and I have never tried it and have been able to work up sub .5 MOA loads without doing either.

Hope that helps and Welcome to LRH!
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  #6  
Old 08-24-2013, 05:28 PM
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Re: bullet seating accuracy

"How do you more experienced loaders get the depth perfect without growing older trying?"

I suspect most experienced loaders know adjusting seating depth more precisely than maybe +/- 5 thou is usually meaningless.
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  #7  
Old 08-24-2013, 07:41 PM
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Re: bullet seating accuracy

5thou out would affect some of my loads.
fireworks, you can seat to exact desired depths, but the trick is in measuring as such.

You can't really measure by COAL even if you qualify bullets by same OAL, due to ogive radius variances. So you'd have to qualify both bullet OAL and bullet ogives before seating.
A better measure is OgvOAL, using a comparator as mentioned. This at least removes bullet OAL as a factor.

I do qualify ogive radius using Bob Green comparators(BGC) Bob Green New Products
And for OgvOAL, I prefer a Sinclair 'nut' SINCLAIR HEX STYLE BULLET COMPARATORS | Sinclair Intl
I seat bullets with under 1thou total variance(ES), and I measure every one.

But the BGCs are expensive and I don't imagine you care to spend so much.
Well the good news is, if you smart in your neck sizing and control over seating forces, you don't have to qualify bullets for seating on the money.
I've done a lot of experimenting, and applied some fancy trig in a big program to figure this out.

With a shorter ogive radius nose, your comparator hit's it's datum sooner, and so would the rifling(from the bullet base), but, the seater stem contacts sooner also. So such a bullet will seat deeper in bearing(in the neck), to provide the same comparator reading and same distance to the lands. The opposite holds for longer radius bullet noses.

The variance left with this, is bullet bearing seated in the neck. I know folks will resist it, but bearing variances(seated or otherwise) are meaningless to internal ballistics.
What is vital to perfect seating though, is rational and consistent seating forces(another thread).
I'll say with high seating forces and variances to it, a seater stem wedges differently, affecting results.
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