Base to ogive variance 6.5cm

Base to ogive variance 6.5cm

This is a discussion on Base to ogive variance 6.5cm within the Reloading forums, part of the Sniping Related category; I noticed some variance in base to ogive measurements for my 6.5 CM 140 Berger and 142 SMK loaded rounds. I suspect the same occurs ...

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  1. #1
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    Base to ogive variance 6.5cm

    I noticed some variance in base to ogive measurements for my 6.5 CM 140 Berger and 142 SMK loaded rounds. I suspect the same occurs with other calibers but I just checked my 6.5CM's when doing a load development for a rifle.

    I believe this is due to the variance bullets have between the ogive and the meplat. Since seating dies do not push the bullet in place at the ogive it stands to reason there would be some variability. I brought this up with the folks at Berger and Forster. Forster sent me another seating stem for my die but even with the new stem, I still had variances of a few thou.

    Since absolute consistency is king in our sport, base to ogive should be consistent in order to have consistent bullet distance to the lands. Has anyone else noticed this?

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    Senior Member straightshooter1's Avatar
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    I know that quite a few seating dies do not use the ogive and therefore are subject to more of that variation you're talking about. But Forster's seating die's does use the ogive, so if you're sorting the bullets by base to ogive measurements, you should be getting pretty consistent seating depth. . . especially with the likes of the 142 SMK. Now, if one is using something like an ELD bullet or some high BC bullets that are long and skinny from the ogive to the meplat, then s special stem needs to be used to get that consistent seating depth along with decent concentricity. This could be an issue with the Berger 140 VLD or the Hybrid . . . huh???

    Until recently, I've been sorting my bullets by bearing surface length and I've gotten pretty consistent seating depths. I've recently change to sorting by base to ogive and have been getting just as consistent seating (+/- .001. . . mostly within .001) using my Forster Ultra Micrometer Seater Die (for my .308 175 and 168 SMK's).

    One thing I have noticed is that when seating and feeling a difference in seating resistance (indicating a difference in neck tension), the seating depth will vary by more than what I want. In some instances, there can be a substantial difference. So, I'm wondering if this might be the issue in your case . . . in that you might be having neck tension variations causing some or all of this???

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    Quote Originally Posted by straightshooter1 View Post
    I know that quite a few seating dies do not use the ogive and therefore are subject to more of that variation you're talking about. But Forster's seating die's does use the ogive, so if you're sorting the bullets by base to ogive measurements, you should be getting pretty consistent seating depth. . . especially with the likes of the 142 SMK. Now, if one is using something like an ELD bullet or some high BC bullets that are long and skinny from the ogive to the meplat, then s special stem needs to be used to get that consistent seating depth along with decent concentricity. This could be an issue with the Berger 140 VLD or the Hybrid . . . huh???

    Until recently, I've been sorting my bullets by bearing surface length and I've gotten pretty consistent seating depths. I've recently change to sorting by base to ogive and have been getting just as consistent seating (+/- .001. . . mostly within .001) using my Forster Ultra Micrometer Seater Die (for my .308 175 and 168 SMK's).

    One thing I have noticed is that when seating and feeling a difference in seating resistance (indicating a difference in neck tension), the seating depth will vary by more than what I want. In some instances, there can be a substantial difference. So, I'm wondering if this might be the issue in your case . . . in that you might be having neck tension variations causing some or all of this???
    I'm not sorting bullets yet and maybe that's the next step... measuring surface contact distance like you do. I cull the rounds that have a different resistance level indicating more or less neck tension when I'm seating. I don't have to do that often but sometimes one goes in too easy or two hard. I make a note of that round on the case with a sharpie and see where it lands on the target compared to its contemporaries. Usually not much of a difference but enough to cause a flier in an otherwise bughole group. I'm in the office now but my recollection is that Micrometer Forster seating die for my 6.5CM is a good bit away from the ogive of both the 140 Berger hybrid target and the 162gr SMKs. Even after they gave me the updated seating stem for the 6.5CM die. I'll check next batch I load to see how far away the seating stem makes contact from the Ogive.

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  5. #4
    Senior Member straightshooter1's Avatar
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    Quote Originally Posted by Martino1 View Post
    I'm not sorting bullets yet and maybe that's the next step... measuring surface contact distance like you do. I cull the rounds that have a different resistance level indicating more or less neck tension when I'm seating. I don't have to do that often but sometimes one goes in too easy or two hard. I make a note of that round on the case with a sharpie and see where it lands on the target compared to its contemporaries. Usually not much of a difference but enough to cause a flier in an otherwise bughole group.
    I used to feel quite a difference in seating resistance pretty often, but for quite a while now I don't . . . not to say there's an occasional one that can seem like a significant difference. I think probably my cases prep procedures has helped improve neck tension consistency. But lately I've toyed with the idea of getting press where I can actually measure the difference in resistance and see how much difference that might actually make for me.

    Quote Originally Posted by Martino1 View Post
    I'm in the office now but my recollection is that Micrometer Forster seating die for my 6.5CM is a good bit away from the ogive of both the 140 Berger hybrid target and the 162gr SMKs. Even after they gave me the updated seating stem for the 6.5CM die. I'll check next batch I load to see how far away the seating stem makes contact from the Ogive.
    When I checked the difference between where my Forster seating die touched the ogive and where my comparator touched, there was/is a substantial difference (like about .150 on a 175 SMK). . . though still considered on the ogive. The same can be said if one compares where the bullet touches the lands and where it touches the comparator. When I talked to Forester about this issue, they explained that since the stem floats inside that bullet channel, there's not enough room to get it all the way down to where a comparator would sit. But it's still considered being on the ogive with very little, if any, difference in terms of any seating variance. As far down on the bullet as the stem does goes and the stem riding nicely in the bullet channel, the seater produces pretty good concentricity and consistent seating depth (especially if one sorts bullets by length of ogive).

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