Shouldn't the measurement from base to ogive be the same or every bullet combination? Once you know one, shouldn't the contact point be the same for any bullet. I used the rod down the barrel method but it hard to get good repeatable readings. The crimped case and bullet inserted is useless as sometimes it sticks in the lands and sometimes it moves while being retracted. Hard to find a good repeatable way of doing this, does the hornady tool work any better?
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Measuring Base To Ogive
- Thread starter rockywlw
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1. No, each bullet's design has the ogive in a slightly different arc/radius, so the measurements will change,
2. The Hornady tool works well, especially if you're not real adept at the other methods you mentioned.
2. The Hornady tool works well, especially if you're not real adept at the other methods you mentioned.
like marinePMI said no....perfect example...im shooting 130g berger hybrids and am going to try some 130g TMKs...
130 berger hybrid base to ogive .700...base of case to touching lands 2.085
130 TMK base to ogive .784...base of case to touching lands 2.104
130 berger hybrid base to ogive .700...base of case to touching lands 2.085
130 TMK base to ogive .784...base of case to touching lands 2.104
The bullet is .308”
The grooves are .308 and the lands are .300
There’s a sloped transition between those two called the lease. Where that sloped transition of the bore and the slope on the nose of the bullet meet depends on each individual combination of angles to where it contacts. You might get close between two and you might get drastically different answers. Only way to know is to measure and check.
The grooves are .308 and the lands are .300
There’s a sloped transition between those two called the lease. Where that sloped transition of the bore and the slope on the nose of the bullet meet depends on each individual combination of angles to where it contacts. You might get close between two and you might get drastically different answers. Only way to know is to measure and check.
I always thought the base to ogive should be the same on every bullet regardless of shape, but I’ve found that is not the case. If I asked anyone why, they usually misunderstood my question and assumed I was talking about coal. I’m still a little confused why a say 250 smk and a 300 smk don’t have the same ogive length.
Because the ogive is specific to a bullet's length/weight. It's an arc or angle (tangent or secant), or both (as is a hybrid) that is based of the length/weight of the bullet and the preferred performance design. This is also why some bullets of the same weight and caliber have different amounts of bearing surface, their ogive (or curve of the bullet point) will determine how much shank remains untapered. Minus the boat tail, this collectively is referred to as the bearing surface (how much of the bullet actually bears against the rifling).
In a perfect world, all bullets in your box of "identical" bullets should have the same exact ogive length.
Unfortunately, machine adjusment, tooling wear, and manufacturing tolerances may cause minor differences in any given lot. These differences may become more significant lot to lot and are easily measured with our calipers.
Easiest way to compensate for the ogive variations is to adjust the seating depth of your new lot of bullets to match the CBTO length measure from your prior lot.
Unfortunately, machine adjusment, tooling wear, and manufacturing tolerances may cause minor differences in any given lot. These differences may become more significant lot to lot and are easily measured with our calipers.
Easiest way to compensate for the ogive variations is to adjust the seating depth of your new lot of bullets to match the CBTO length measure from your prior lot.
simple answer....because the 300g SMK weighs 50g more than the 250g SMK so that extra 50g has to go somewhere...obviously they can not make the bullet fatter so they make it longer.
You know I’m talking about distance to lands with a seated bullet and not the bullet itself right?
yes...your question is(if im understanding correctly) "why do all bullets not seat the same distance from the lands"?
right?
left 130g berger hybrid
center 130g TMK
right 140g berger hybrid
so the bergers are both hybrids and from what i understand so is the TMK but dont quote me on the TMK because it dont really look like it to me.
the 130g berger is 2.090 touching the lands in my rifle
the 140g berger is 2.085
the 130g TMK is 2.104
the TMK has .083 more baring surface than the 130g berger and .063 more than the 140g berger...also note that even though they are all hybrids they have a slightly different looking ogive...also the press that the bullet is made on can vary as well as other machining differences.
i dont know if that helps any.
center 130g TMK
right 140g berger hybrid
so the bergers are both hybrids and from what i understand so is the TMK but dont quote me on the TMK because it dont really look like it to me.
the 130g berger is 2.090 touching the lands in my rifle
the 140g berger is 2.085
the 130g TMK is 2.104
the TMK has .083 more baring surface than the 130g berger and .063 more than the 140g berger...also note that even though they are all hybrids they have a slightly different looking ogive...also the press that the bullet is made on can vary as well as other machining differences.
i dont know if that helps any.
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Okay, I think what is being missed in this discussion is that simple fact that the ogives on different bullets are at different diameters than each other and are also mostly different than the diameter of the included circle formed by your lands. Therein lies the answer to your question.
Yes, different loads should all exhibit the same distance from base to your lands, but ogive diameters are rarely the same as your lands diameter.
Yes, different loads should all exhibit the same distance from base to your lands, but ogive diameters are rarely the same as your lands diameter.
Here's a discussion about ogives by AB. Note the first paragraph in the section titled "How Ogive Curves are Defined".
http://www.appliedballisticsllc.com/Articles/ABDOC2.1 - OGIVECOMPARISON.pdf
http://www.appliedballisticsllc.com/Articles/ABDOC2.1 - OGIVECOMPARISON.pdf
Okay, re-reading what I wrote a few posts above, I realize that I didn't really describe what I meant, so here it is in pictures. And it differs a bit from what I said above.
So, as the pictures show, what we are often referring to as the ogive, is not the same as the caliber or land to land dimension, because we are really usually referring to as ogive just happens to be the diameter of our measuring tool. Notice that the Hornady comparator insert measures .2475" (roughly, since calipers are not the best measuring device for this application), but it is marked .26, indicating its intended use for 6.5/.264 caliber rounds.
The land to land diameter of your barrel for that caliber should be nominally .264", making that disparity the reason for the question, the confusion and discussion. The disparity is the roughly 0.016" in diameter difference between the comparator measuring point and the actual caliber diameter of the bullet (most commonly referred to as the ogive). The location, lengthwise, of that measuring point on different bullets varies considerably (in relative terms).
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Lash, you are certainly correct about the tool used for measuring being incorrect. In fact, some of those inserts are actually cone tapered. I am referring to the Sinclair inserts in particular. I use the Redding instant indicator, so I use the bushing corresponding to land to land. For a 6.5/.264 caliber, the land to land measurement is .256, a .308 is .300, and .338 is .330
I ordered one of the Hornady tools and I will do some more checking. I still have a hard time seeing how different bullets will have different base to ogive length since all the bullets will contact the lands at the same diameter. The video above looks so easy but in reality does not work that way. I did my RPR 10 times and got 10 different answers. I'm interested to see how the Hornady tool works and of its repeatable.
I used to use the Sinclair tool until I got suspect measurements compared with the soft seating method. Truth is, there is no foolproof method to doing it, and to expect conclusive results in one try is quite ambitious
Lash, back to your post from earlier, what's got me confused is that if the diameter of lands is .300, a .308 bullet should stop movement forward where the ogive is .300. I'm sorry I don't do well with abstract things, and I am sure I would understand it better if we could draw it on paper
A .308” bullet will hit the lands before they are their tightest diameter of .300, at a land dimension of .300 a .308 bullet will be .008 jammed. The lands taper from .308 to .300
I’m this picture you can seen the area marked “lead” with the circular scratches where the lands are removed entirely. In “throat” you can see the scratches disappearing as the lands taper from removed to their full height.
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Yeah. The grooves are the diameter of the lands removed. The freebore should be pretty freaking close to it with in reason to not be a press fit.
Half a thou over in this particular reamer print for googles quick return
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Yeah, I think it’s usually a 1.5-2.5 degree angle or so. This article has this great illustration
http://riflebarrels.com/a-look-at-bullet-ogives-and-chamber-throat-angles/
You know what is so funny about this? I first brought up this question back in 2011 and asked a bunch of people including Redding. I eventually gave up and just accepted it for what it is. But not one person ever said to me, "because the lands are tapered". That would've solved everything 7 years ago.
Yep. It’s all tapered.
The lands are tapered and the tools are tapered because a perfect sharp angle diameter will dig it before giving a consistent reading.
Because it’s not a perfect angle and diameter between every reamer and every tool they are not headspace gauges or seating gauges, they are comparators. They won’t give you an absolute measurement but they will provide a consistent reference diameter datum to measure your personal set up with your particular tools and materials. That’s why we say bump back .002 or size down to .002 beneath loaded diameter or .020 off the lands instead of giving a hard number of 1.628 shoulder measurement or .338 neck or 2.3174 seating depth. My tapered tools won’t return those same measurements.
The lands are tapered and the tools are tapered because a perfect sharp angle diameter will dig it before giving a consistent reading.
Because it’s not a perfect angle and diameter between every reamer and every tool they are not headspace gauges or seating gauges, they are comparators. They won’t give you an absolute measurement but they will provide a consistent reference diameter datum to measure your personal set up with your particular tools and materials. That’s why we say bump back .002 or size down to .002 beneath loaded diameter or .020 off the lands instead of giving a hard number of 1.628 shoulder measurement or .338 neck or 2.3174 seating depth. My tapered tools won’t return those same measurements.
You don't need to be exact. You just need to get in the ball park to start your bullet seat depth testing.
At the end of the day, you are still going to take out some rounds with the bullets loaded at different seating depths. The gun and rounds down range will be the ultimate judge on what your base to ogive length will be.
Everything is relative to the specific rifle, so I wouldn't get hung up on having to be exact. All the other stuff is noise once you get that load shooting.
I have used the Hornady tool and find very easy and repeatable to find base to ogive. I still don't understand why but all 3 bullets I tried do indeed have a different base to ogive. The other thing nice is the 6.5 case from Hornady has the exact same base to shoulder of my fired brass, that's was a surprise. I would recommend that tool to anyone.
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