Ogive Measuerment???

Originally Posted By: pyscodogOriginally Posted By: VarminterrorThe Hornady modified cases are useless in the way they instruct them to be used. Unless you reference the modified case against a once (or twice/thrice) fired case and add or subtract the appropriate headspace length, they're 100% useless - just a shot in the dark. All they really let you do is measure from the chamber shoulder to the lands - there's no guarantee with the bolt open that your headspace length on the modified case is the same as your actual rounds. Used properly, having the shoulder datum to lands datum distance is really valuable, but that's not how hornady's instructions read.

I started to dis-agree but after thinking on this, your actually only measuring from the shoulder to the lands. Correct?

Right - When you shove the modified case into the chamber, you HOPE it's headspacing on the shoulder as it should (usually is), so then all you are doing is pushing the bullet up against the lands. So what you know, at that point, is the tool is locked with the bullet ogive datum line the proper length from the headspace datum line. The distance from there to the base of your case is 100% arbitrary.

So, as Greg mentioned, you can have Hornady make a modified case from your once fired brass, or make your own. But then you have to have a modified case for every rifle you own.

What I do - I reference my once fired brass against the Hornady Modified Case (or my homemade version of the same).

So...

I measure the headspace for my once fired brass case
I measure the headspace for the Hornady Modified Case
I use the OAL tool with the bullet in question to measure:
COAL of the Hornady MOdified Case + my bullet in question
Ogive to Headspace length of the Hornady Modified Case + Bullet in question
I then add or subtract the difference between my once fired case and the Hornady Modified Case to get my once fired "kiss the lands" COAL with the bullet in question
Subtract my desired bullet jump and I have my target COAL using THAT BULLET
Then I use a bullet comparator to determine the case base to ogive length (this should be constant for all bullets, as this should be the distance from the bolt face to the lands)

What that basically does: Sticks the headspace to ogive length measured with the Hornady tools onto the proper headspace (base to datum) length for my once fired brass.

So if my hornady case = 1.470" headspace, but my chamber is long at 1.473", and I measure 2.225" COAL using the hornady case and a bullet, I know I have to increase to 2.228" COAL with THAT BULLET to actually fit my chamber - then subtract my desired jump, say 15thou, giving me 2.213" COAL. Then I measure the Ogive-to-base length (bolt face-to-lands + jump) length) with a bullet comparator so I can replicate that ogive-to-base length with the rest of the bullets in the batch.

Technically - I know I can use that same ogive-to-base length with ANY bullet.
 
Can't you drill out a once fired case and stretch the neck? Would this be more accurate then? Do seating dies measure from the tip of bullet or from the ogive? I thought they all measured the same way...from the tip? That's why you get a different reading at times...because all bullets aren't the same length. Right or wrong? (again)
Thanks for all the replies!
Gene
 
Originally Posted By: gene10pntrCan't you drill out a once fired case and stretch the neck? Would this be more accurate then? Do seating dies measure from the tip of bullet or from the ogive? I thought they all measured the same way...from the tip? That's why you get a different reading at times...because all bullets aren't the same length. Right or wrong? (again)
Thanks for all the replies!
Gene

Yes you do drill out a fired case. If it is too tight to let the bullet move through easily go in with a Cratex and lightly ream the inside of the neck. You probably don't have an expander button that would allow you to increase the size of the neck from the inside as it is already expanded to larger than bullet size in most cases.

Dies don't measure anything. The seater on various brands and various calibers will be higher or lower on the bullet. The good ones are hollow in the center and let the bullet ride up until the ogive is encountered. The RCBS will sometimes impinge on the bullet tips flattening them out. For those long pointy ones you can get special seaters. Some of the seaters will crease the bullet as they don't meld at the same angle as the bullet ogive and at times you have to go in and smooth the cup to fit the profile.

Greg
 
Originally Posted By: Varminterror
Technically - I know I can use that same ogive-to-base length with ANY bullet.

Not really.

You might, if...

If your comparator just happens to match the geometry of your chamber throat. Which is not likely. Even if you had a stub gage made when the barrel was chambered, even it won't match the actual geometry once you start shooting and wearing the throat.

If the other bullets have the same ogive as the one you used to measure, some will, but some likely won't - tangent vs. secant, radius, there are variations, each of which will give a different measurement on the same comparator.

The comparator/ogive measurement is obviously much more consistent and vastly superior to measuring off the tip. But it's not transferable between bullets as many seem to think.

- DAA
 
Originally Posted By: DAAOriginally Posted By: Varminterror
Technically - I know I can use that same ogive-to-base length with ANY bullet.

Not really.

You might, if...

If your comparator just happens to match the geometry of your chamber throat. Which is not likely. Even if you had a stub gage made when the barrel was chambered, even it won't match the actual geometry once you start shooting and wearing the throat.

If the other bullets have the same ogive as the one you used to measure, some will, but some likely won't - tangent vs. secant, radius, there are variations, each of which will give a different measurement on the same comparator.

The comparator/ogive measurement is obviously much more consistent and vastly superior to measuring off the tip. But it's not transferable between bullets as many seem to think.

- DAA

Well said DAA.

I just pulled the specs on my American 30. Measuring nine bullets in the same chamber with the same case using my Sinclair tool I got nine different distance to lands. These varied from 1.049 to 1.442. Actual loaded overall length varied from 2.103 for a Sierra 110 FMJ to 2.389 for a Remington 150.

I tried some Speer 200's and the were DTL at 1.049 (note the shortest) and the loaded OAL was only 2.322.

There are very few things in reloading that are identical across the board when it comes to bullets and chambers.

Greg

By the way a Sierra 110 FMJ was 1.442, the Sierra 110 HP was 1.379 distance to lands.
 
Originally Posted By: DAAOriginally Posted By: Varminterror
Technically - I know I can use that same ogive-to-base length with ANY bullet.

Not really.

You might, if...

If your comparator just happens to match the geometry of your chamber throat. Which is not likely. Even if you had a stub gage made when the barrel was chambered, even it won't match the actual geometry once you start shooting and wearing the throat.

If the other bullets have the same ogive as the one you used to measure, some will, but some likely won't - tangent vs. secant, radius, there are variations, each of which will give a different measurement on the same comparator.

The comparator/ogive measurement is obviously much more consistent and vastly superior to measuring off the tip. But it's not transferable between bullets as many seem to think.

- DAA

YEP
 
I ordered the Sinclair tool and AR guide....every body I've talked to says this is better than the Hornady...will give it a try. What is a good distance to start at seating from the lands then??? Do most rifles like some bullet jump before going into the lands??? Putting bullets right up to them will cause high pressures...correct? Hope I'm reading the books right!!!
 
If you can reach them I start at the lands and then back off 0.005 increments. If I can't reach them I load as long as I can and then shorten up. Pressures from seating are an inverse Bell curve. Load very short and pressures go up. Push the bullet out further and pressures drop. Keep getting closer and closer to the lands and in them and the pressures go up again. Not necessarily linear but close in many instances.

Most Sierra's don't mind a long jump. Some bullet shapes like VLD's (Bergers in many cases) like to be very close to the lands though lately Berger reports that many are jumping them. I won't unless I have to but they are a specialty bullet in my world. The monolithics like the Barnes need to be backed of quite a bit from the lands or pressures will rise on them

Greg
 
Ditto.

Bottom line, if you are going to tweak it later, you only want to go one direction. Easiest path is starting as long as is reasonable/possible for the application. It's the atypical bird that actually shoots better with significant jump vs. in or nearly in the lands. It happens, but it's not the norm. So start as long as you can, given the parameters of your specific application.

- DAA
 


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