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Posted: 4/6/2012 9:13:37 AM EDT
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Ok, it's been awhile since I've loaded some finished rounds.
Equipment: RCBS jr press. Basic C-frame press. RCBS seating die. Seats and kinda roll crimps in a single step. Anyways, I got my die set up how I wanted it, ran a couple to be sure it was working properly, no problem. First 3 rounds are 2.260 exactly, overall length. Great. The fourth round is 2.264. Fifth is 2.263. Sixth is 2.255. Fifth is 2.262. What's going on here? There's no debris on the face of the shell holder or on the stem of the bullet seater. I made sure they were clean before I started. Is the bullet seating stem contacting at a different point on the bullets or what? These are pulled 63 grain milsurp bullets, if that makes any difference. I wouldn't ordinarily care about 4 or 5 thousandths of difference, but these are for some home made snap caps. Why such a wide difference? It's gotta be the bullets, I'm thinking. That, or the calipers. BUT, I don't think it's the calipers because they give the correct (and repeatable) reading when I measure the length of my LE wilson case gauge. Any ideas on what the problem is? |
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I thought about that, but the more I thought, the more it seemed like that couldn't be the difference considering that the relevant points of contact here are:
-The circumference at a certain point on the bullet's tip to the seating stem -The base of the case with the shell holder Wouldn't a difference of bullet length result in more or less bullet on the inside of the case? |
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This is almost always caused by inconsistencies with the bullet shape. Most, if not all rifle caliber seaters index on the ogive of the bullet, not the tip. Cheap bullets, poor quality bullets, or mixed bullets won't be consistent on the ogive, which is why you have inconsistent OAL measurements. |
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Quoted:
This is almost always caused by inconsistencies with the bullet shape. Most, if not all rifle caliber seaters index on the ogive of the bullet, not the tip. Cheap bullets, poor quality bullets, or mixed bullets won't be consistent on the ogive, which is why you have inconsistent OAL measurements. It's seating on the ogive. I can see the mark. Would a stem that pushes alot closer to the tip help? |
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Quoted:
Quoted:
This is almost always caused by inconsistencies with the bullet shape. Most, if not all rifle caliber seaters index on the ogive of the bullet, not the tip. Cheap bullets, poor quality bullets, or mixed bullets won't be consistent on the ogive, which is why you have inconsistent OAL measurements. It's seating on the ogive. I can see the mark. Would a stem that pushes alot closer to the tip help? Not really, and the variances you're seeing won't likely make a huge difference if the variability is coming from the bullets anyway. So long as you've got sufficient space that you're not jamming them into the lands (and if you're loading for an AR mag, you will have plenty of space), they should be fine. Realize that you're measuring to the tip of the bullet, and your chamber doesn't care where the tip is. It cares where the ogive meets the lands. You'll see this less with match-grade bullets, but even those will have some variability in the distance from ogive to tip. The only way to see if it's coming from your die would be to measure to the ogive using something like a Stoney Point (now Hornady LNL: http://www.6mmbr.com/catalog/item/1433308/977259.htm). |
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Quoted:
I thought about that, but the more I thought, the more it seemed like that couldn't be the difference considering that the relevant points of contact here are: -The circumference at a certain point on the bullet's tip to the seating stem -The base of the case with the shell holder Wouldn't a difference of bullet length result in more or less bullet on the inside of the case? The seater stem should touch the ogive of the bullet, not the meplat. It's possible that a really old, pre VLD stem could contact the meplat, but it's not likely that you have one. Therefore, every bullet is seated an identical length into the case, no matter how the COAL turns out. This is what you want, don't readjust the seater to make the COAL identical. Of the cartridges in the first post, three differ by 0.002 inches - that is trivial. Manufacturing processes require tolerances in the individual detail parts, and in the assembly. That's just the way it is. Your thumb is worth at least 0.0005 inches on the caliper, too. |
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