Seating Depth: COAL or Ogive?

[SPIKER]

I'm an Ogive guy myself, Using a bullet compensator, I make sure that my Ogive is the same on my different heads to ensure the same contact with the lands regardless of bullet length.

Any thoughts?

[Enigma]

Ogive seems like the best method to me, assuming you have the space and reliable feeding for a longer round. I imagine that during the start of powder ignition, a non-moving bullet is going to allow for a steady case volume and therefore a steady pressure rise. A moving bullet will change the volume and lower the pressure until it hits the lands. How much this minor, but early pressure stumble actually effects the overall ignition time, pressure and consistency is well beyond my knowledge - but in a precision distance round at least, I can easily believe it has a measurable effect.

How the gun is designed and built affects this too. I bought an AMT 45 DAO "backup" when they came out years ago and took it to the range to put a couple hundred ball rounds through it. After seeing the gun performed flawlessly, I started carrying it, with Hydrashocks. It would not be for nearly a month that I would get a chance to shoot the Hydrashocks and find out they did not feed most of the time. It was Ogive. The bullets were wider than ball towards the front and the steep ramp of the little AMT wasn't able to deal with feeding them. My simple solution was to set up my press with a smaller die (think it was .38), using a ball round to set the die depth. I then ran the Hydrashoks through the press and seated each bullet a little deeper so the profile of the Hydrashock would closer match that of the ball round. I went though hundreds of rounds reseated like this, and they all ran fine.

[dsdmmat]

A majority of my loads are limited by magazine length so I COAL.

[EvilD]

OAL for me

[Meketrefe]

We refer to COAL as the Cartridge Overall Length. The cartridge overall length is taken from an average of several measures. So one first should take the bullets only
and then understand the spreads in the bullets. Modern bullets with polymer tips might show little differences when measured from the tip while spear points
and soft point bullets with lead exposed might show larger differences. Also open tip match or varmint bullets that have not been uniformed (or pointed) might show
some substantial differences from the burrs / excess left by folding the jacket cup. That is why match competitors point them and not for the COAL because they
will not use that measure but to make sure they expose the same precise profile and more efficiency in the air. Good match bullets are already concentric and well
made so this is just an addition to fix the tips.
But no matter what when you measure from the tip it is a relative measure. Only if you take several measures you can take that as 'ok' but not perfect.
I say ok because if you take a measure with an uniform bullet and take the average you will be very close for many purposes but never will be able to replicate
a previous seating depth unless one uses a seater with a micrometer or the seater die is a regular die but with a locking system to lock the seater in the same
position and never move it. It is also a good idea to keep a round of your accuracy load as a template so you can transfer that round seating depth to another round.

You see when you seat a bullet with a large taper (ogive) the die will use that taper as the position to seat that bullet. So in reality after measuring a bullet from the tip
given is the approximate value after seating the first one the rest will be the same precisely because they are seated from that taper and because if a seater
mandrel used the tip it could deform the tip and will not give any consistency at all. So it is up to us what we choose to start the first round or calculate the average
from the total lenght but thereafter the bullets are produced consistently by seating from the ogive.

So that is why folks who really want accuracy and perfect carbon copies will also use the taper and a special die and take the first measure/s from the ogive using
a bushing adapter for that purpose. One exception to this is folks that use the seater dies with micrometer that might use the micrometers reading to do the precise
adjustment and they never change the locking ring in the die. but still a small adjustment might be necessary and they always use the ogive measure.
This doesn't mean that one has to do this all the time and an average taken from the tip for certain type of bullets (ie: amax) might be pretty darn close but again
will not really safe anytime if one wants to get a good average so, again, might just go to the bushing or micrometer to make sure you get a true measure.

Seater die with micrometer...




Regarding the COAL / magazine limit the limit will be always dictated by 4 factors: the maximum seating capability of the case and die, the magazine maximum length,
the chamber so we do not end up jamming or at least not jamming unwanted length into the lands, and finally the limit of the action / firearm to allow that firearm
to cycle reliably unless it is a single shot. So unless single shot or double barrel one also might choose to feed manually if the magazine cannot handle it or
look for a special magazine that allows longer bullets.

So every exception, every variation might have a reason and a purpose but if one wants to replicate accurate rounds one needs to measure from the ogive.
Make a choice between that and other methods is making a choice between consistency and potentially accurate ammo and not so consistent and not so accurate
ammo, and that is ok if it is not needed like plinking, some hunting, average use, etc...

Simple Hex Nut bullet comparator bushing...

[SPIKER]

Excellent write up. I use a Forster Micrometer seater, and have to take certain rounds from the batch and adjust .001 or so depending on seating depth. It seems that all bullets are not created equally. I use the Hornady OAL gauge, and the the bullet comparator, along with a digital caliper to get a precise distance off the lands.

Using the ogive measurement I can get .005 - .050 or whatever the rifle likes off the lands. I have had loads that like 1.05 off the lands while other loads like .010. Every rifle is different, but you have to find the sweet spot with a particular round.

[Meketrefe]

Excellent write up. I use a Forster Micrometer seater, and have to take certain rounds from the batch and adjust .001 or so depending on seating depth. It seems that all bullets are not created equally. I use the Hornady OAL gauge, and the the bullet comparator, along with a digital caliper to get a precise distance off the lands.

Using the ogive measurement I can get .005 - .050 or whatever the rifle likes off the lands. I have had loads that like 1.05 off the lands while other loads like .010. Every rifle is different, but you have to find the sweet spot with a particular round.

Thanks.
I think secant ogive are more forgiving while some tangent ogive like the VLD bullets are "jump" sensitive. So for those one might consider a load slightly touching the lands.
But yes the gauges measuring from the taper is the only way to assure consistency. Nothing someone going plinking needs to consider but so folks understand that the only
way to make sure is by.... making sure .. and that involves proper process and tools.