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ogive confusion...

 
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  #1  
Old 02-26-2013, 12:24 AM
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Location: Texas
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ogive confusion...

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?
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Old 02-26-2013, 12:52 AM
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Location: Texas
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Re: ogive confusion...

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
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Old 02-26-2013, 07:34 AM
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Re: ogive confusion...

Quote:
Originally Posted by J E Custom View Post
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
JE, wouldn't something like the RCBS precision mic, round specific, give you the exact measurment you need?

Thanks,

Doc (another roookie!)
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Old 02-26-2013, 09:33 AM
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Re: ogive confusion...

Quote:
Originally Posted by DocB View Post
JE, wouldn't something like the RCBS precision mic, round specific, give you the exact measurment you need?

Thanks,

Doc (another roookie!)

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
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  #5  
Old 02-26-2013, 10:00 AM
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Join Date: Oct 2012
Location: Windsor, VA
Posts: 294
Re: ogive confusion...

Quote:
Originally Posted by J E Custom View Post
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
J.E.

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

Thanks again!

Doc
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  #6  
Old 02-26-2013, 10:14 AM
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Join Date: Jan 2013
Location: Meridian, Idaho
Posts: 1,296
Re: ogive confusion...

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.
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  #7  
Old 02-26-2013, 12:52 PM
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Join Date: Apr 2012
Location: The cold part of Montana
Posts: 1,390
Re: ogive confusion...

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.
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