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Posted: 4/10/2017 12:56:16 AM EDT
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I saved the bullets I used to measure max OAL using my Stoney Point (Hornady) gage. It measures 0.660" from the base to the ogive. Using that bullet, the bullet jams into the lands at 2.034".
I measured some bullets from a new (different) lot. The new lot jams into the lands at 2.052", almost 0.020" longer. It's not throat erosion, as I have the original bullet and re-measured using it. I mention this because many people (like me) want to load to 0.010" off the lands. The problem is the lot-to-lot bullet variations are 0.020" all by themselves. So, always measure using bullets from the box you are loading. |
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Quoted:
What brand/part # bullet? I was surprised at the magnitude of the difference. I would not have thought twice about a few mils difference from lot-to-lot perhaps due to a different die being used,... but 20? Hmmm. I am going to make a bunch more measurements today when I get a chance (bullet base to ogive). I want to better understand the variability within the lot and from lot-to-lot. I'm going to open some other boxes, too, just to check. |
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Forget COL to start with. Its a number based off the tip of the bullet, and not a given point in the ogive of the bullet instead.
Hence until the bullets have been ogive meplat trimmed and tipped, you cant use a COL number since you have variances from the ogive contact point, to the end of the bullet tip (can average .015" on most pre meplate trimmed and tipped HP bullets). Also, remember that your Stoney gauge Ogive device will not engage the bullet the same way as the rifling will, so you first have to determine how far out you need to seat a specific type bullet in the case for a kiss to lands to start with to come up with a zero base number for that bullet type and lot. So Zero Base line will always be the specific bullet type and lot first determined for a kiss to lands in the rig, then measured with your Stoney gauge ogive device to determine a Ogive OAL measurement, then that can be shorted by .010" for the jump. Also, before you start just coming up with a jump number (I run them at .003", since my press will hold less than .001" ogive OAL variances), you have to first determine what you machine will hold in variances in Ogive OAL's. Hence most will state to hold a .010" jump, since most machines will have a variance is Ogive lengths up to .006" instead. So at .010" as the longest ogive OAL for jump, they might end up with .004" ogive OA's in the lot, which still keeps all the bullet in the reloaded lot from embedding on loading. And if you where wondering, in a HPBT bullet, it wants to jump less than .008" to be really happy instead. |
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Quoted:
Sierra 6mm 107 gr MatchKing I was surprised at the magnitude of the difference. I would not have thought twice about a few mils difference from lot-to-lot perhaps due to a different die being used,... but 20? Hmmm. I am going to make a bunch more measurements today when I get a chance (bullet base to ogive). I want to better understand the variability within the lot and from lot-to-lot. I'm going to open some other boxes, too, just to check. |
| This situation starts anew every time a different bullet forming die is used. They are never exactly the same, never identical, regardless of manufacturer. No manufacturer will use a single bullet forming die to make every bullet, one after another. They make batches in mind boggling numbers every day. Sometimes you get lucky and find a lot that vary less than the slop in your calipers and the inadvertent variance in your technique. |
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I'm surprised to see that out of a Sierra bullet. Hornady or Speer wouldn't surprise me, but Sierra does. Any chance there was a design change since you bought the one that were .660? Here's another one for you. How do you deal with throat erosion and the ever-increasing distance to the lands? Do you chase the throat, keeping the same amount of jump? Do you load per the original OAL, keeping the internal volume the same? |
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Quoted:
This situation starts anew every time a different bullet forming die is used. They are never exactly the same, never identical, regardless of manufacturer. No manufacturer will use a single bullet forming die to make every bullet, one after another. They make batches in mind boggling numbers every day. Sometimes you get lucky and find a lot that vary less than the slop in your calipers and the inadvertent variance in your technique. I think I may start collecting lot numbers as part of my reloading info. |
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Quoted:
Agreed, that's what prompted me top start the discussion - the surprise. Here's another one for you. How do you deal with throat erosion and the ever-increasing distance to the lands? Do you chase the throat, keeping the same amount of jump? Do you load per the original OAL, keeping the internal volume the same? |
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