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Old February 20, 2019, 12:22 PM   #1
jetinteriorguy
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Proper way to use a rifle micrometer seating die

I've been using my Forster seating dies for both my .223 and 6.5 Creedmoor and getting some wide variances of up to .010" which seem a bit much. So I've loaded some up trying a different method. I back off my die by .010 and seat, then measure each round and reset the die down however many clicks to reach my desired depth. This has produced ammo that has stayed within .0005" of my desired depth. I'll shoot these this week to see if this makes much difference. Just curious if anyone else does this.
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Old February 20, 2019, 12:40 PM   #2
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The reason you are seeing the COAL variance is due to the bullets coming off different lines at the factory. Even Sierra MatchKings exhibit this. When I was shooting 1,000 yard F Class, I never worried about it. More important than the COAL is the distance from the bullet ogive to the lands. Remember, there is a large portion of the bullet ogive (including the meplat) that never make contact with the bore. Hope that helps.

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Old February 20, 2019, 01:02 PM   #3
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Quote:
Originally Posted by jetinteriorguy View Post
I back off my die by .010 and seat, then measure each round and reset the die down however many clicks to reach my desired depth.
Are you measuring case head to ogive (or shoulder to ogive) using a comparator?

If not, your revised method is likely inducing *increased* variation in the measurement that's important (that is, the distance between the ogive and the lands, be it positive or negative).

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Old February 20, 2019, 01:27 PM   #4
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Rox hit it. I've measured match bullets and found the distance from the tip to the bore diameter on the ogive (the place that contacts the throat) varies substantially. If you are aiming at constant COL you are not getting the consistent bullet jump you want.

The seating dies contact the bullet somewhere on its ogive, and not its tip. That's why you see the COL variation shows up. 0.010" is about normal for .30 cal hollow point match bullets. I've measured some with 0.015" tip-to-ogive variation.
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Old February 20, 2019, 01:58 PM   #5
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You definitely need to get a comparator if you don't already have one. As stated, bullet length can very by .010 pretty commonly. even within the same box.

Also as already stated The important place to be consistent is the distance from the ogive to the lands. If you use a comparator to measure length you will likely see .002 or less variance. At least thats what I get with Hornady eldx and Sierra game kings
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Old February 20, 2019, 07:44 PM   #6
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Sorry for the lack of info. I'm measuring CBTO using the Hornady system, not OAL. I've never gone by OAL except within magazine limits, but even then I'm measuring it CBTO and allowing enough for bullet differences to still fit in the mag.
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Old February 20, 2019, 08:09 PM   #7
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VLD's ?
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Old February 20, 2019, 08:42 PM   #8
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I have only ever had that much difference on one occasion. Some 140 grain Nosler BT. They varied by as much as .036 in bullet length

I sent photos to Nosler of the different measurement of the various bullets from the same box. They were interested to figure out why. Anyway they sent m a new box of bullets.

Aside from that once. I haven't had Cartridge base to Ogive vary more than .003.

My guess would be either that box of bullets is out of spec. Or there is something going on with the die.
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Old February 20, 2019, 10:11 PM   #9
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jetinteriorguy,

What is going on here is the location where the seater stem makes contact with the bullet ogive is not in the same location as your Hornady tool, hence the variance. Typically the seater contacts the bullet ogive well above the point of the ogive where CBTO measurements take place.

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Old February 20, 2019, 10:49 PM   #10
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It could be that or the shape of the bullet. Forster says their standard seating stem works with about 90% the bullets out there, but the other 10% will need a custom stem to work their best.

If you can't spot a ring where the stem hits the ogive, I would mark up a bullet with Magic Marker ink and seat it to identify where the contact is being made. If it's on the tip of the bullet or close to it, which can be the case with a VLD or some secant ogive designs, then you need to send the bullet to Forster to get a stem made for it. Call them first.
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Old February 21, 2019, 06:12 AM   #11
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I guess as usual I'm not quite communicating well. I do understand about how the bullets can vary a little, and how the contact point of the seating stem can affect seating depth. The main thing I'm curious about is how people work around this. Basically I've just started backing off the seating stem, seat the bullet, measure the depth, then screw the stem down however many thousandths it takes to get the needed depth. So, is this a common practice or just something that's not such a big deal? Thanks, Les.
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Old February 21, 2019, 08:49 AM   #12
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Quote:
I do understand about how the bullets can vary a little, and how the contact point of the seating stem can affect seating depth. The main thing I'm curious about is how people work around this
https://www.youtube.com/watch?v=6VGp0At_k-I
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Old February 21, 2019, 09:38 AM   #13
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jet,

Just set your seater die up so that it produces the same CBTO dimensions that you got with your Hornady OAL Gauge with the same bullet. You are over thinking it.

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Old February 21, 2019, 10:10 AM   #14
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USSR,

the OP indicates he gets 0.010" variation on his bullet comparator readings of the finished ammo that way. I don't think I typically get more than about 0.003" variation from a box of match bullets doing that.


Jetinteriorguy,

Do you have a case comparator to see how consistent your head-to-shoulder measurement is after resizing? If so, take your loaded rounds and make the case head-ogive-measurement and the case head-to-shoulder measurement. Subtract one from the other. The zeros won't match, but since the case headspaces on the shoulder, it will tell you how consistent your actual bullet distance off the lands is.

For myself, that error is small enough that I ignore it and don't try to seat bullets so close to the lands that a few thousandths would mean the difference between contact and no contact. In load development, though, when I often try to get as close to zero inconsistency as I can, your approach is pretty much what I use. I measure shoulder and ogive and sort by the difference, then use the micrometer adjustment to bring them all in to match the shortest reading.
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Old February 21, 2019, 12:43 PM   #15
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I do have a comparator and will check to see what variances might be between the shoulder and bullet ogives. I hadn’t factored in this relationship to see how consistent it will be. I know sometimes I may seem to overthink things, but for me it’s a big part of why I enjoy the reloading hobby. I would like to thank Houndog and Uncle Nick for all the first rate help and patience they have had in helping me with some things this winter. You have my respect.
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Old February 21, 2019, 05:18 PM   #16
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Quote:
the OP indicates he gets 0.010" variation on his bullet comparator readings of the finished ammo that way. I don't think I typically get more than about 0.003" variation from a box of match bullets doing that.
Well, you lucked out on that box of bullets Unclenick. I was getting up to 0.010" variation in comparator readings with Sierra MatchKings, until I started sorting my bullets.

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Old February 21, 2019, 06:02 PM   #17
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I use Forster Micrometer seating dies for calibers for my most accurate rifles.
I measure every round after it is seated using a Hornady comparator.
I do see some variations but nothing a large as the OP is seeing.

However, I would suggest that the occasional variations I do see come not from bullet variations but:
1) older brass that has been reloaded multiple times so an occasional neck tension is looser than the other brass in the load.
2) the trim length of one brass is much longer or shorter than the norm I was working to
3) the powder is being compressed so much that it begins make the bullet rebound after seating
4) I get a bit too enthusiastic with the press lever arm

When things go right, I can get each load of 25 rounds to measure +/- 0.001 on the comparator readings. I'm happy with that much variation because it will cause a velocity variation of about 1 fps, which is far less than the primer powder combination firing variations that I would expect.
When they don't, I sometimes get a round that is within 0.005 inches of the desired median.
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Old February 22, 2019, 06:05 AM   #18
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This is something new.

http://bulletin.accurateshooter.com/tag/base-to-ogive/
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Old February 22, 2019, 11:04 AM   #19
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All of my seating dies are micro adjust; most of my dies require I add the micro adjust and then there is that thing about getting all of them to agree when comparing and verifying.

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Old February 22, 2019, 11:35 AM   #20
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Quote:
Originally Posted by USSR
Well, you lucked out on that box of bullets Unclenick.
It's not the bullets themselves that are usually responsible, as the seating die (I was using a Redding Competition seater) hits the same ogive diameter every time and that diameter is pretty consistent in its distance from the part of the ogive below it that touches the lands. Maybe a 0.001" variation or so. The bullets themselves varied about 0.008" from ogive to base (see below), but in the loaded round, the longer ones just get seated that much deeper. The 0.002"-0.003" loaded round variation in the shoulder datum-to-ogive distance was a combination in the small ogive form difference and variation in the location of the shoulder datum distance from the case head after resizing. That adds about the same error as the bullets have.

Here's what I got from 15 150 grain Sierra MatchKings. Note that I used two different bullet comparator inserts for the base-to-ogive measurements. The taller result is from a Hornady (actually, an original Stoney Point) aluminum insert, while the shorter measurements are from a Sinclair stainless steel insert which was cut with a throating reamer or something very close to it, so it gets down where the actual contact with the lands is made. Both inserts will fit either the Sinclair or the Hornady caliper adapters. The only difference is the Hornady adapter is offset for reading off their length gauge, while the Sinclair holder is centered on its caliper jaw slot.

Attached Images
File Type: gif 150 gr SMK 2015-04-16b.gif (16.1 KB, 175 views)
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Old February 22, 2019, 02:12 PM   #21
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Quote:
...the seating die (I was using a Redding Competition seater) hits the same ogive diameter every time and that diameter is pretty consistent in its distance from the part of the ogive below it that touches the lands.
Well, Nick, I use the very same seating die. The problem I've found is the seating stem makes contact with the bullet ogive well above the part of the bullet ogive that the comparator and the barrel lands makes contact with, and the variations between these 2 points on the bullet ogive show up in the CBTO measurements. I'm afraid we are going to have to agree to disagree on this one my friend.

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Old February 22, 2019, 03:38 PM   #22
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You have a process problem. One part of the process is bullet seating.....my +/- 3 sd is about 0.006”, I think....actually, I had better calculate that....regardless, it is rare to observe 1 over 0.005” off nominal.

Therefore, I think you will find you have neck tension problem. Have you tried running cases through a neck expander after fl sizing? Have you checked neck thickness variation?
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Old February 22, 2019, 06:21 PM   #23
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I full length size with a Redding body sizing die, followed by Neck sizing with a Lee collet sizing die. All my necks are turned to the same thickness and trimmed to the same length. So my method of starting long and then turning the die down the appropriate amount made a big difference. I also added a light crimp with the Lee collet crimp die. I shot five- five round groups doing seating depth testing and the worst group was 3/4" and the best was 3/8" at 100 yds.
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Old February 22, 2019, 07:09 PM   #24
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Do you get any marks on the bullet from the seating stem?
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Old February 23, 2019, 05:14 AM   #25
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Just a barely noticeable mark on the 140gr ELD M's in my 6.5 CM, but on my Hornady 68gr HPBT's in my .223 it does get a noticeable dent around the bullet where the stem makes contact. I may have to have a custom stem made for those bullets since they still shoot 1/2-3/4 MOA in my .223.
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