Why does OAL to Ogive vary?

[4xforfun]

First....I didn't read all of the responses above, so if this has been covered, .....

If you could take your seating stem out of your die and fit it some way to the measuring tool and then measure your base to "ojive" with that...(which probably isn't really the ojive, but it will be the same place on the bullet since you are using the actual seating stem)...then your OAL base to ojive would be IDENTICLE...less the run out in the press and run out in the measuring tool. Your measuring tool and your seating stem are different and touch the bullet at different places on the bullet, and there is run out in the actual shape of every bullet to some degree....that is where your varience comes from.....PLUS the runout in your press and measuring tool.

Just my take,
Tod

 

[msinc]

First....I didn't read all of the responses above, so if this has been covered, .....

If you could take your seating stem out of your die and fit it some way to the measuring tool and then measure your base to "ojive" with that...(which probably isn't really the ojive, but it will be the same place on the bullet since you are using the actual seating stem)...then your OAL base to ojive would be IDENTICLE...less the run out in the press and run out in the measuring tool. Your measuring tool and your seating stem are different and touch the bullet at different places on the bullet, and there is run out in the actual shape of every bullet to some degree....that is where your varience come from.....PLUS the runout in your press and measuring tool.

Just my take,
Tod

Well yeah, but he still hasn't said how much of a difference he is finding....what you are referring to and what I am talking about would be a few thousandths.....he might be talking about .010" or .020". In that case it has to be something different.

 

[4xforfun]

Well yeah, but he still hasn't said how much of a difference he is finding....what you are referring to and what I am talking about would be a few thousandths.....he might be talking about .010" or .020". In that case it has to be something different.

Like I said....I didn't read the entire post. I apologize.

Tod

 

[msinc]

Like I said....I didn't read the entire post. I apologize.

Tod

I really didn't mean for an apology...none is needed at all. I was just agreeing with you and pointing out the fact that he has yet to disclose what he is calling a difference in length.

 

[Papa Charlie]

Here are the readings I get using my comparator and the Hornady OAL length gauge for different types of rounds.

2.343 175 SMK
2.367 155 SMK Palma
2.385 185 Juggernaut

 

[Average joe]

Here are the readings I get using my comparator and the Hornady OAL length gauge for different types of rounds.

2.343 175 SMK
2.367 155 SMK Palma
2.385 185 Juggernaut

What XTR said.........your comparator is not the same diameter as your lands. None are.
So when your bullet is touching the lands, you are measuring a place on the bullet further up on the ogive, and using that value as a reference.
Theoretically, If you had a comparator that was the exact diameter of your lands, all of your cartridge base-to-ogive measurements would be the same for all bullets. I think that is what you're struggling with.

 

[spclark]

Theoretically, If you had a comparator that was the exact diameter of your lands, all of your cartridge base-to-ogive measurements would be the same for all bullets.

Right on!

And that comparator you refer to is colloquially referred to as a ‘gizzy’: a short piece of barrel blank into which your choice of reamer has been run into, so that you have an exact duplicate of your chamber’s throat and lead (where lands begin tapering from full bore dia., at least when your chamber’s fresh & new!) that you can use to measure this kind of thing more accurately than any ‘off-the-shelf’ comparator like Hornady’s.

 

[Papa Charlie]

Thanks for the responses, as I have been reading and inputting information it has clicked in.

 

[4xforfun]

Right on!

And that comparator you refer to is colloquially referred to as a ‘gizzy’: a short piece of barrel blank into which your choice of reamer has been run into, so that you have an exact duplicate of your chamber’s throat and lead (where lands begin tapering from full bore dia., at least when your chamber’s fresh & new!) that you can use to measure this kind of thing more accurately than any ‘off-the-shelf’ comparator like Hornady’s.

Which works when your BBL is new. Run a couple hundred rounds down the tube and it isn't "exact" anymore.

My smith gives me one with every new bbl he chambers up for me.

Tod

 

[Richard Coody]

if you really want to learn buy you one of these or some other model

https://www.sinclairintl.com/reload.../sinclair-bullet-sorting-stand-prod38769.aspx

and compare the different bullets you use. then compare 50 or so of the same bullet.

it should be enlightening

 

[spclark]

Which works when your BBL is new. Run a couple hundred rounds down the tube and it isn't "exact" anymore.

Well, no, that’s true enough.

Still, at the very start you can use it to tell you what the difference is (in 0.000x”) between using it and a Hornady-style gauge to measure seating depth once those lands begin to move... which can be useful info.

 

[Papa Charlie]

You all have got me thinking now. I just sent Benchmark a RFQ for a comparator that would be the same as the lands on the barrel they are making me. Sure it will change over time but might be worth it depending on what they want for it.

 

[XTR]

You all have got me thinking now. I just sent Benchmark a RFQ for a comparator that would be the same as the lands on the barrel they are making me. Sure it will change over time but might be worth it depending on what they want for it.

The point at which a bullet touches will depend on the angle of the lead and the shape/angle of the nose of the bullet. You are over thinking this. Exactly where/what the measurement happens to be is not important, what is important is that you have a way to quantify that distance and determine where your seating depth is in relation to it.

 

[Brians356]

"ojive"

LOL You're either channeling Richard Pryor, or, like me, you're a stickler for correct pronunciation. I could write "jigabytes" on that subject.
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