Measuring From The Ogive For the First TIme...

[RLinNH]

...and I am shocked at the results! I have only been loading now for a little over 5 years. I have always measured my C.O.L. from the head of the bullet. Over the years I have read here that it is much more accurate to measure from the ogive. I took a leap and purchased a Forster Datum Dial Kit. I am not all that solid on this kit as it does have movement in the measuring area due to the ball/detent on the dial. Anywho, I seated 60 Lapua Scenar 139 grain bullets today. I set one bullet at my desired C.O.L. (2.820) and then took a measurement with the dial set on .264. Went to town for 60 cartridges. Checking each cartridge for C.O.L. I feel that I am anal when it comes to C.O.L. After I got done seating all the cartridges, I checked them from the head of the bullet. WOW!!! Reason I went to this cannelure seating measurement was because I noticed, about 3 months ago, that my bullets had "issues" with not being consistent as far as the head of the bullet. I noticed that quite a few of the bullets had small imperfections in them with the head having a small metal copper "flake" bulging at the head. And after checking the C.O.L. at the head of the bullets AFTER seating them with the ogive, I am noticing as much of a .0045" of a difference in my cartridges. Is this normal? And yes, I like this way of seating the bullets a lot better. I would like a better "Datum" though as, like I said earlier. This Forster System has a small ball detent in it and I feel that there may be as much as a .0010" bounce. But then again. Press firmly, and I'm good for now.

 

[ma smith]

This chart may facilitate your conversation. The area typically you would measure with comparitors, is around the 'ogive' listed on the chart below. A machinist or gunsmith could be more specific.

A cannelure is typically located on the bearing surface, IIRC.

 

[Baron23]

...and I am shocked at the results! I have only been loading now for a little over 5 years. I have always measured my C.O.L. from the head of the bullet. Over the years I have read here that it is much more accurate to measure from the cannelure. I took a leap and purchased a Forster Datum Dial Kit. I am not all that solid on this kit as it does have movement in the measuring area due to the ball/detent on the dial. Anywho, I seated 60 Lapua Scenar 139 grain bullets today. I set one bullet at my desired C.O.L. (2.820) and then took a measurement with the dial set on .264. Went to town for 60 cartridges. Checking each cartridge for C.O.L. I feel that I am anal when it comes to C.O.L. After I got done seating all the cartridges, I checked them from the head of the bullet. WOW!!! Reasoning I went to this cannelure seating measurement was because I noticed, about 3 months ago, that my bullets had "issues" with not being consistent as far as the head of the bullet. I noticed that quite a few of the bullets had small imperfections in them with the head having a small metal copper "flake" bulging at the head. And after checking the C.O.L. at the head of the bullets AFTER seating them with the cannelure, I am noticing as much of a .0045" of a difference in my cartridges. Is this normal? And yes, I like this way of seating the bullets a lot better. I would like a better "Datum" though as, like I said earlier. This Forster System has a small ball detent in it and I feel that there may be as much as a .0010" bounce. But then again. Press firmly, and I'm good for now.

As mentioned, you are measuring to the ogive. I have no idea about this Forrester tool but most fixed diameter tools to measure to the ogive are called bullet comparators as two diff makes may have slightly different angles cut and result in slightly diff measurements. But if used to measure distance to lands and the same one is used to measure cartridge base to ogive (CBTO) you are good.

As for setting your tool to .264, have you put decent calipers on the bearing surface (see ma smith’s graphic)? I bet it’s smaller than .264.

Cheers

 

[RLinNH]

As mentioned, you are measuring to the ogive. I have no idea about this Forrester tool but most fixed diameter tools to measure to the ogive are called bullet comparators as two diff makes may have slightly different angles cut and result in slightly diff measurements. But if used to measure distance to lands and the same one is used to measure cartridge base to ogive (CBTO) you are good.

As for setting your tool to .264, have you put decent calipers on the bearing surface (see ma smith’s graphic)? I bet it’s smaller than .264.

Cheers

As far as Calipers are concerned, I am using Mitutoyo Calipers. And yes. That's a damned good idea. Going downstairs right now to measure the diameter of the .264 opening

 

[Baron23]

As far as Calipers are concerned, I am using Mitutoyo Calipers. And yes. That's a damned good idea. Going downstairs right now to measure the diameter of the .264 opening

Cool. If I recall correctly, the Berger 140 hybrid targets I shoot are a very consistent .2635

The problem with measuring COAL and using that figure is you can have significant difference in bullet overall length due to small variation in the meplat (tip of the bullet 2 small opening). I have not taken measurements myself, but I understand this variation can be as much as 5-7 thousandths.

Now, I’m no ammo manf expert by any means but I do understand this arises from the process of copper jacketing the core and there being slight differences in how that pointy end is formed. That and the ogive, being where the bullet interfaces with the rifling, is not only far more consistent it’s also the only figure we are really interested in when determining jump and trying to tune a load via seating depth. Aside from mag length considerations, I’m not sure that COAL is meaningful in any way.

There are others here gM far more expert than I on reloading metallic ammo so take what I say with a grain of salt.

Best of luck.

 

[redbullitt]

Eye opening right lol?

Ive had good enough luck with the Hornady comparator setup. Its measuring from ogive IF you have the right bushing. Its not primo level shit, but does make a difference to me as i shoot a lot of pulled match bullets.

A bucket of 168 smks sure can bring some variety to the table when measured by ogive.

 

[RLinNH]

Just fixed the title of the thread. Thank you to those of you that corrected me.

 

[RegionRat]

Over the years I have read here that it is much more accurate to measure from the cannelure.

Not sure where or what that meant, but it isn't true anyway.

Sometimes, the bullet manufacturer's were coerced into adding a cannelure to their match bullets for DoD spec purposes. Those dimensions are arbitrary and too gross to use for referencing seating depths.

As a beginner, you already know that the tips of many bullets can be variable and less important to accuracy.
Not long ago, some match bullets began to use plastic tips which may not be as rough as open tip match bullets, but are still inconsistent.

(Keep in mind, way down the road the bullet length is important when we "point" them, so don't get confused if you read things that mention sorting bullets by over all length.)

Your comparator tools may or may not reference the ogive in the same way that your rifle and chamber do, and that is okay.
It is important to be consistent with your method and seating depth even if the reference is arbitrary.

For medium level students of reloading for accuracy, I think it is a good idea to make and keep a reference dummy cartridge with a representative bullet seated to your initial estimate of the light jam or touch point. Using the stripped bolt method to set that depth is easy and reliable, but get help if you are not used to stripping the bolt or more importantly, reassembling it.

At every session, use the dummy round as a QC check of your comparator tools and depth settings. You can then just "zero" on that reference and measure all your seating depths against it for the life of that barrel.

 

[DownhillFromHere]

I haven't waded too carefully through all that has been said here, but the bottom line is this: forget measuring COAL / COL (Cartridge Over All Length / Cartridge Overall Length) because, as Baron23 said, open-tip meplats vary in length.

You're measuring CBTO (Cartridge Base To Ogive) because this measurement is supposed to be more consistent than COAL - so why measure COAL at all? You gain nothing from it. What you want is a consistent CBTO measurement, within a thousandth or two of your target.

I remember LONG ago loading up some 77gr Sierra Match Kings and noticing a couple of the meplats looked "jagged." The length of a half a dozen bullets varied by as much as .004 inch. I had two boxes of 500... the "jagged" meplats were, and are, the norm for SMKs and, to whatever extent, pretty much every open-tip bullet I've loaded.

 

[Molon]

I am not all that solid on this kit as it does have movement in the measuring area due to the ball/detent on the dial. . . .. This Forster System has a small ball detent in it and I feel that there may be as much as a .0010" bounce.

Not if you tighten the bolt that holds the datum wheel.

....