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How accurate should COL be?

 
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  #15  
Old 10-15-2011, 04:39 PM
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Re: How accurate should COL be?

Coal is seated from the tip while jump is seated from just ahead of the major radius. you need a seating cup that pushes the bullet at its major diameter then the oal length wont be the same between rounds but the actual jump will be. pick which you want and modify the cup and or the seating die accordingly
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  #16  
Old 10-15-2011, 05:02 PM
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Re: How accurate should COL be?

Quote:
Originally Posted by ken snyder View Post
Coal is seated from the tip while jump is seated from just ahead of the major radius. you need a seating cup that pushes the bullet at its major diameter then the oal length wont be the same between rounds but the actual jump will be. pick which you want and modify the cup and or the seating die accordingly
I think I get what you are saying. By major radius I imagine you mean what people usually call the ogive?

Are there any companies that make dies which seat using the ogive rather than the tip of the bullet?
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  #17  
Old 10-15-2011, 07:16 PM
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Re: How accurate should COL be?

The term 'ogive', relates only to the curve of a bullet nose. That is, the curve type and amount, expressed in cals of radius.
It is NOT a datum on a bullet nose.

Shooters assume that the 'begining' of a bullet nose section, or 'end of bearing', equals the ogive and the point where first contact is made with the barrel leade. But this is not an established datum(a standard). Nobody official has has declared that OgvOAL equals casehead to 1thou under cal, or 5thou, or 20thou. In fact, I just made up the term OgvOAL, without qualifying it at all...
Also, the first contact point to leade is completely dependent on leade angle-vs-ogive shape. And there is no standard w/resp to datum in either seater plugs or OAL comparators.
It's all realative.

BUT, there are trends with reason.
Comparators generally take a datum near cal diameter, but not so close as to cause inconsistent readings from varying measure pressure.
Seater plugs contact quite a bit further down the nose, and with greater contact area, because there is way more pressure applied in bullet seating. So higher gripping angles are called for -to push against. But if you excessively size necks there can still result enough seating force to damage bullet noses, and cause variances in seating depth.

I for one am glad seater plugs are just the way they are, and I'm sure this was the result of trial & error testing by die makers. If the seater plug contacts too high on a bullet nose, especially a tangent ogive nose, the contact angles become so shallow that consistent seating would be impossible without very low seating forces(about as much force as we measure OgvOAL with).
A seater plug can be lapped for better seating, but with atleast as much contact lower on the noses.

I do wish there was a standard datum that all comparators and seating plugs were then based on..
siegrisj, when you make ammo you should have no problem getting far better numbers than those Federals.
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  #18  
Old 10-15-2011, 08:11 PM
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Re: How accurate should COL be?

Ive been looking for that word "Ogvoal "for a long time, I vote we coin it. Mikecr said basically the same in greater detail. If all the pressure required to seat the bullet is on the very small tip the tip will deform, the cartridge length will not change but how deep the bullet is seated into the case will. If the pressure bearing surface of the seating cup in the dies makes contact lower down on the bullet it will not deform. The closer to the actual diameter or further down the bullet the seating cup makes contact the better. If you were to measure my bullets you will find that the vary in total length but the Ogvoal is the same on all of them
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  #19  
Old 10-15-2011, 11:35 PM
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Re: How accurate should COL be?

Ok, I mounted the press properly and loaded up some more. Here were my numbers in order. There were a couple I had to make adjustments for on the die because they were coming out too long. Otherwise I tried to load them without making adjustments on the die.

2.227
2.226
2.230
2.228
2.226
2.228
2.227
2.225
2.228 (Had to make an adjustment on this down below the 2.23 range)

2.227
2.223 (here is a good example of a large jump. I didn't touch the die here.)
2.230

2.225
2.226
2.227
2.226

I sorted them and compared them next to the Federal. The consistency seems to be comparable. 2.227 was the length I was going for. It works out to a ~2.8 COL.

Interesting that these are 175gr bullets and the numbers that I posted for the GMM were 168gr.

Mikecr says I should have no problems beating the Federal loads, so far it looks like they are comparable. What needs to change do you think?

Thanks for the input everyone.
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  #20  
Old 10-16-2011, 04:32 AM
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Re: How accurate should COL be?

Even the very best custom made bullets will have variance at the ogive. Major brand boxed bullets are even worse. Here is what I do: Bought a white poly loading block from Sinclair, then number each line on the side from one to ten. Also, bought a Davidson base and nose piece of each caliber I shoot. These are like the comparator, and attach to caliper jaws.

Set each bullet depth to about .005 or so above desired depth with these tools and note the appropriate line on my Redding competition seater. I seat each on ogive, and place it in the block on a line which is marked 1-10 thous above my desired depth. I do ten at a time. After I know how many thous over desired depth, I move the seater down a thou at a time with each new row, beginning with line marked 1 (.001") , until all are seated exactly the same. This does not work well with compressed loads, beacuse the tight powder column will push the bullets back up a few thous. This is time consuming, but it will give you very accurate loads.
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  #21  
Old 10-16-2011, 08:46 AM
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Re: How accurate should COL be?

Siegresj keep in mind that we are looking for a sweet spot for accuracy. We talk about length knowing it is important but not as important as the sweet spot which is very forgiving of exactness. Here is a little trick a lot of us do out of habit and forget that it is even being performed. Dont seat your bullet all in 1 stroke of the press. Seat about half way then lift the handle off the cartridge and spin it about 90 degrees then seat all the way with second stroke, doing this will yield a more uniform length and a straighter bullet. P.S. factory box ammo is for the tourists, you are off to a good start!
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