Seating Off The Ogive

[nicky]

I understand that seat off the nose of a bullet you get a more consistant OAL but bullet depth can be inconsistant.  Seating off the ogive gives you a more consistant seating depth while giving you a inconsistant OAL.

My question is how much of a variance in OAL do you expect seating off the ogive.

[Wobbly]

I would say that depends upon the anvil used to seat the bullet. If you got an anvil that fits very tightly, then the numbers will be better. If you use a RN anvil to seat a conical nose bullet, then the OAL (and concentricity) tolerance numbers could be much higher.

 

[ReloaderFred]

There are also variances in the length of bullets, even from the same lot.  During the manufacturing process, parameters are set for minimum and maximum tolerances for the product, which would be a bullet in this case.  As long as the product falls within those tolerances (the +/- from zero specified) then it's within "specs". 

If you measure a sampling of bullets from a lot, you will find there are sometimes minute differences in the lengths from base to nose, but all those bullets will be "in spec".  Some people get all hung up on trying to get the same exact OAL of their loaded rounds, but what really affects accuracy is the distance between where the bullet contacts the ogive, and the volume of the combustion chamber.  The more consistent that distance and volume are, usually the more accurate the ammunition is.

Trying to get a slightly longer bullet to the exact OAL as a slightly shorter bullet affects the volume of the case, too.  Not much, but still there is a difference in pressure inside the case, due to the different volume INSIDE the case between the two rounds, when all else is the same.  The average shooter will never be able to tell the difference, but it's there.  Shooting from a machine rest is where it usually shows, where the human factor has been removed from the equation.....

Hope this helps.

Fred

[IDescribe]

How much of a variance in OAL do you expect seating off the ogive?

I expect cartridge variance to be equal to bullet variance itself PLUS a few thousandths.


Nicky, the amount of variance in OAL when seating off the ogive is heavily dependent on the variation in the bullet itself because in most bullets, most of the variation in bullet length occurs at the nose.  FMJ is probably the exception.  It's basically going to be bullet variation plus YOUR variation, based on your arm and your gear.

As others have said, the variation in remaining case volume/combustion chamber affects precision negatively.   Variation in how far the ogive is from engaging the rifling when in battery can affect precision negatively.  Both of those variances are maximized by seating off the nose.  Both of those variances are minimized by seating off the ogive.  It's best to minimize those variances. 

I'll also add that you might not see huge results at normal pistol distances, AND there are a number of other factors that will have a significantly greater impact on precision.  Going back to what Fred said, it's one of those things that's more likely to show up with mechanical testing than off hand, but if you know it's the better option, and it's no extra effort to insert the ogive anvil than it is the flat anvil, why not use the ogive anvil? 

[tdogg]

This is all assuming that the variations in length are past the ogive.  I've seen bullets that the opposite was true, where the overall bullet length was consistent but the base to ogive distance was not.  Get a bto comparator and figure out where the bullet length variation originates then pick your seating anvil.

If your chasing that type of accuracy in a pistol you are a better shot than I am.  Do they make true ogive seating anvils for pistol dies? 

Cheers,
Toby

Sent from my XT1254 using Tapatalk

[1SOW]

As Fred described,  getting the same seating depth is the key to consistency. 
I've got a batch of PD JHP 124s that were a tenth" off lengths due to bullet "nose" inconsistencies.  The body of the bullet seems fairly consistent but not easy to measure,  so an anvil the seats low on the ogive would likely give good results.
I gave up trying to manipulate the oals.  My load pressures make it safe to just seat the dern bullets and press on.  They still shoot very well.
I'm anal about reloading inconsistencies,  and have been spoiled by using bullets that have been at close tolerances.


  Any bullets I load close to max loads are premium SD types that all check to close tolerances. 

[nicky]

Sorry about not getting back to this post for a few weeks.

So if the bullets run a range of let's say .666-.669 in length then I should expect that my OAL would vary by at least .003 but my seating depth would be consistant dependent on the meatball pulling the handle.

Thanks once again.

[snakeye]

Lee Precision will make you a seating stem to fit their Lee bullet seating dies to match the ogive of the bullets you use. You mail them a request along with the bullet you are using and they will make it, around 10 bucks IIRC. This will help some on consistency.

[copemech]

Zo what is your typical OAL variation? Mine seems to be in the .005 range, but that is why we back off .015 from push limits.

[Wobbly]

It's probably four or five variables all adding up together. Some run to the plus side while others run to the minus. But in the end, your OAL should be able to be within +/-.003", unless you're using hollow points that have the lead spill out the jacket.

You best results will be with flat nose using a flat anvil, and that's probably where you should test yourself. If you're OK there, then you'll be doing good everywhere else, no matter what the caliper is saying.

 

[1SOW]

Just to add another variable to handle pull consistency:  with a turret or single stage press your "range pick-up" cases,  even with the same headstamp,  will be harder or softer than others using the feel on the handle pull as a gage.

If a case has been shot and reloaded several times,  the handle pull down will " feel" different than a once fired brass.