ogive confusion...

Discussion in 'Reloading' started by Texas Republic, Feb 25, 2013.

  1. Texas Republic

    Texas Republic Well-Known Member

    Messages:
    157
    Joined:
    Aug 27, 2009
    I have a question that I need some clarification on concerning accurate reloading and the ogive. I recently ordered Hornady's ogive comparative tool. I understand the ogive to be what really matters in measuring jump or the amount of bullet that rests in the rifling once chambered. And that seating depth goes by this measurement and not the OAL of tip to bottom. This allows the reloader to precisely record the measurement that a certain accurate load is seated to. For some reason, I cant quite wrap my head around bullet prep. What I mean is how to make sure every round is consistently the same OAL from bottom to ogive.

    Do I only measure each bullet from ogive to bottom and separate any inconsistency before seating them? This is the only thing I can think of at this point, because seating the bullet should be the exact same as long as each bullet is the same. This is because the seating die should seat from the ogive every single time. Therefore, if all of my bullets have the same ogive measurements, setting the die up once and seating them all without adjusting it should produce consistent loads without any variance in the OAL of my ogive. Does all of this sound right?
     
  2. J E Custom

    J E Custom Well-Known Member

    Messages:
    7,307
    Joined:
    Jul 29, 2004
    That is correct.

    Different bullet shapes loaded to the same ojive length (Land diameter of a .308 will be .300 and bore dia will be .308.) use a .300 bushing and measure to the back of the case for the correct
    dimension.

    Cartrige overall lengths will vary depending on the bullet type used, But the ojive length needs to remain the same to maintain bullet to land clearance.

    CAUTION; Bullet seating dies will engauge different bullets at different points and may change ojive
    lengths so when changing bullet styles you have to check the ojive to case head length to maintain
    proper bullet to land clearance.

    I hope that cleared it up for you.

    J E CUSTOM
     

  3. DocB

    DocB Well-Known Member

    Messages:
    425
    Joined:
    Oct 7, 2012
    JE, wouldn't something like the RCBS precision mic, round specific, give you the exact measurment you need?

    Thanks,

    Doc (another roookie!)
     
  4. J E Custom

    J E Custom Well-Known Member

    Messages:
    7,307
    Joined:
    Jul 29, 2004

    Im sure it would Doc.

    I use a combanation of tools by hornady to measure the chamber to land dimension and the cartrige
    to land dimension.

    The hornady lock and load bullet compairator fits on your vernier and has inserts that are standard
    calibers and can measure the length of your case to land dimension. there overal length gauge
    (Looks like the old stoney Point gauge)along with the modified case to match your chamber does
    a good job of measuring the chamber to land dimension of your rifle.

    Both cost around $60.00 and make a great addition to ones reloading equiptment.

    There are other brands and methods to get these dimensions but these work well and are easy
    to use and understand.

    I looked up the product # on Midway if it will help to see both. #231904 and #570611.

    I used to use a neck sized case with a the bullet of choice lightly seated long and just tried it and
    kept shortning it in my dies until it would chamber. this worked but was not very accurate and I
    had to assume that the bullet was slightly into the lands and back off .005 to .010 thousandths .

    Now that we can buy the proper tools, no more guessing.

    J E CUSTOM
     
  5. DocB

    DocB Well-Known Member

    Messages:
    425
    Joined:
    Oct 7, 2012
    J.E.

    Kewl!! Thanks for the numbers and I'll look them up tonight!

    Thanks again! :)

    Doc
     
  6. BrentM

    BrentM Well-Known Member

    Messages:
    1,550
    Joined:
    Jan 10, 2013
    I think you might be getting confused with those of use who separate bullets into lots by ogive. This is actually by bearing surface. We take two ogive bushings and sandwhich the bullet. That measurement tells us if the bearing surface is uniform bullet to bullet. So far the last few lots have been really close but I had 1 lot that had 3 different bearing surface measures with a total spread of .030. That is a bad lot and those bullets will not group well. In that case you can simply lot them and shoot that lot but not mix the lots.

    I also weight sort but I don't see much if any advantage in that so far. .1 or .2 grains has shown little difference on impact to 1000 yards. Ogive bearing surface though, does make a difference.
     
  7. Joe King

    Joe King Well-Known Member

    Messages:
    1,390
    Joined:
    Apr 29, 2012
    I think I'm reading the question a bit different.

    Your thinking that if the ojive is consistent that the cartridge OAL should stay the same as long as every bullet is seated the same distance from contacting the lands (assuming the bullets are of same manf and style i.e. 7mm 162 Amax )? While that would be ideal that isn't how it happens. The area of the Ojive that you want to worry about is the area where your comparator and your seating plug, and your rifling contact the bullet. Forward to the tip of the bullet from that point doesn't matter beyond the down range effect the minor change in BC will have. And it's dman near impossible for bullet manufactures to control the very forward end of the bullet Ojive and tip. You can however, if you trim the tip and point the bullet, but if your hunting with these bullets I would not do that as it can (and probably will) change everything about terminal performance

    As others have stated, you'll be better off worrying about the bearing surface length, one intersting thing I have noticed with quality bullets like Berger, or customs, and mass manf to a lesser degree. Is that if you sort them out to say about 0.002" in bearing length they'll be really really consistent in weight too.
     
  8. Texas Republic

    Texas Republic Well-Known Member

    Messages:
    157
    Joined:
    Aug 27, 2009
    Ok. I may be a little over my head now. Here is my problem. I load a 175gr SMK at 2.80 COAL. I adjust my die usually on the first bullet to get this legnth. From what I understand, you don't want to keep adjusting your seating die up and down to reach a 2.80 COAL once loading rounds bc your ogive will vary. Keeping the seating die the same will produce bullets with the same ogive OAL. This is assuming of course that each bullet ogive is the same.
    When I do this I will get very different COAL on many rounds. I assume it's bc the differences between the ogive and tip of many bullets. That's fine.

    I ordered the bullet comparator to ease my mind and measure each bullet ogive prior to seating them so I know they will rest in the rifling the same. If the COAL is different then so be it. But right now I have no idea. I just know that some will measure 2.80 and others 2.72. That bugs me.

    My thought process correct?
     
  9. woods

    woods Well-Known Member

    Messages:
    965
    Joined:
    Jun 4, 2006
    I was wondering about this once so I did some checking on the ID of the comparators and the approx ID of the seating stem where it would hit the bullets. All of my comparators are .011" below caliber

    Here is a 308 caliber comparator and it is .297" tight on the pin

    [​IMG]

    Now seating stems probably vary quite a bit, but we all have observed that they seem to hit the bullet about halfway toward the tip. I only checked one since all my seaters are locked in and I don't want to take them apart, but the 308 seater die hits the bullet at approx .260"

    [​IMG]

    so to me it would be more accurate to gauge your bullets as you seat them with the comparator and adjust your seating as you go along than to set your seater at one place and leave it there. Not to be anal about getting each bullet down to the .001" OAL but because during a string of bullet seating, connections on the press and dies can change slightly.

    YMMV
     
  10. Broz

    Broz Well-Known Member

    Messages:
    8,637
    Joined:
    Feb 3, 2007
    I apologize for not reading the entire thread but will ad this and hope it has not been suggested.

    If you want more consistent seating depth , head to o-give, set the seating die up to slightly cam over against the shell holder at the top of the stroke. This will lessen the effect of how hard you stroke the handle in relation to the depth it seats the bullet.

    Jeff
     
  11. Red hunter

    Red hunter Well-Known Member

    Messages:
    193
    Joined:
    Jan 1, 2012
    Idealy then using a seater stem that is .300 for a .308 would be ideal. If your comparator is actually .300. this would be the only way to sort bullets and seat them identically ??? Or did I analize this wrong?
     
  12. BrentM

    BrentM Well-Known Member

    Messages:
    1,550
    Joined:
    Jan 10, 2013
    Hmmmm too much analyzing going I think. After getting the comparator, set the seating die to seat the bullet the correct distance off the lands by measuring the base of the case to the ogive of the bullet. Once that is done, you are done until you change bullet brands or possibly even lots.

    For example I have 2 boxes of 100 bullets from the same lot that I will not change my seating die depth on until I change lots or different bullet. I simply measured the bullet ogive to case base using my Hornady OAL guage, subtracted .075, and it gives me a number such as 2.585 - .075 = 2.510 set the die to seat the bullet to 2.510.....done.
     
  13. Joe King

    Joe King Well-Known Member

    Messages:
    1,390
    Joined:
    Apr 29, 2012
    yes that is what I was saying, the only other option I can see is to get an adjustable reamer and ream out your comparator and seater plug to have the exact same inside dia as your lands. Hell I might do that now that I think of it.
     
  14. Joe King

    Joe King Well-Known Member

    Messages:
    1,390
    Joined:
    Apr 29, 2012
    I wonder if you went up 1 or 2 cal on your seating stem if they would contact the ojive closer to the comaritor and where the lands contact without contacting the meplat. Something to think about.