Base to ogive help pls

The Oregonian

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Recently got my new custom 30-06...shoots great with the load that was developed as part of the build.

The recipe calls for a base to ogive of 2.581...the loaded rounds that came with the gun measure with a few thou of 3.294 and I assume the different OAL is due to different ogive points on the bullets (Nosler BT 180gr).

I just bought a bullet comparator from Darrell Holland...It didn't come with directions but it is pretty easy to find the relative lengths of several bullets that are measured. It doesn't give OAL of bullet but it does give a relative measurement like a concentricity gauge does.

My question is how to measure to get the right CBTO measurement. Some bullets are a touch longer so I assume the OAL would be longer by that same amount, but that assumes I have a starting point that says that for a bullet of x length, the ogive is y" from the tip or base of the bullet.

Am I missing something with the comparator (pictured below)? Should I measure the COAL of a round and hen pull the bullet to see the bullet length and use that as a starting point?

Any help is appreciated.

Thanks.
 

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bob4

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The difference in measurements you have? Are you measuring the Ogive of one of the loads built for you for the rifle with your new tool? As long as they fit in the magazine I wouldn't worry about OAL at all just build to match the Ogive measurements given you. Also are you sure your using the correct comparator for the 30.06? Sorry if that seems like a silly question.
Just my thoughts.
 

FearNoWind

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I think we'd better clarify some terms before we get too deeply engaged in this conversation.
CBTO is the distance from the base of the cartridge case to the ogive of the bullet. The distance to the tip of the bullet is not a factor in that data collection process.

Bullet base to ogive has no effect on either of those measurements.

The instrument you have is quite valuable for sorting bullets by "bullet base to ogive" lengths. But it won't provide you with CBTO information unless you can move that bushing out far enough to get a cartridge case with a seated bullet between the dial indicator and the bushing. Even then, unless you can ensure that the bullet doesn't move inside the neck while setting up the measurement you can't be certain of the validity of the data.

To gather CBOL data you need something like:
http://www.midwayusa.com/product/76...l-length-gage-modified-case-30-06-springfield
and
http://www.midwayusa.com/product/57...-length-gage-bolt-action?cm_vc=ProductFinding
and
http://www.midwayusa.com/product/23...ad-bullet-comparator-basic-set-with-6-inserts
along with a good caliper.

Once you get to that point, don't expect the CBTO of the loaded rounds you have to compare with those that you intend to load UNLESS the bullets are the same caliber/style/weight/manufacturer. Bullets differ (even bullets of the same caliber from the same manufacturer from lot to lot) so avoid complacency when you're collecting comparative data.
 
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Dr. Vette

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FNW is correct. I use the second tool he linked to, and purchased additional inserts for extra calibers.

With the Hornady tool plus a good micrometer you can measure the CBTO length on the rounds that you were provided with the rifle. Don't rely just on the measurements you were given, as different tools will yield different results. Once you have the CBTO of the loads you can then load yours to match.

Does that make sense?
 

The Oregonian

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Thanks for the clarification...I am not sure how to even measure the ogive with this tool. It seems like the first and only thing it touches is the tip of the bullet so it would seem to only show the difference in bullet OAL.

I will call a Darrell tomorrow...I assume if I take the avg COAL measurements of the 15 loaded rounds I have and then load to that, that would (hopefully) be close enough to get me within a few thou of the CBTO length as the COAL all seek to be within about 5 thou.

The developed load shot ~.4 MOA so hoping to keep near there. I would like to get a much better understanding of the CBTO but don't want to hold up range time due to lack of loaded rounds in the meantime.
 

WapitiBob

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OP, forget the OAL and measure from the case base to the ogive as instructed. You need nothing but a set of calipers and a bullet comparator set, referenced as item no 3 in fearnowinds post.
The comparator you reference is for bullets only.
 

Mikecr

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What's important above all is understanding.
WapitiBob hit the correct approach leading to this.

The Holland tool holds no application here, and OP has no need to measure the 'bullet relationship to the lands' with a Hornady tool.
He needs only to measure his known good ammo with any CBTO comparator and log it. Doesn't matter that his numbers won't match the makers, just that he has local numbers logged, that he can reproduce from now on(a baseline).
It's simple.
CBTO absolutely can be matched with any and all components. It's 'cartridge base to ogive'.
All cases have a base, and all bullets have an ogive. As long as you use the same CBTO comparator, any one of them you happen to have, you can reproduce target CBTO -with that same comparator.
 

FearNoWind

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..CBTO absolutely can be matched with any and all components. It's 'cartridge base to ogive'.

I believe I understand your point Mike. But I've found that trying to explain to new reloaders that CBTO isn't enough all by itself (because bullet weights, bullet lengths, bullet bearing surfaces, etc. vary widely even in the same caliber caliber) they sometime become confused. Even with matching CBTO, longer bullets will often be seated deeper into the case and/or the COAL will be different. Those factors affect accuracy and if they're not fully understood can be frustrating. Therefore, I advise them to avoid comparing CBTO on a factory round with the ammo they're reloading and to just remain consistent with logging and tracking data for the bullets and cases they're putting together.
 

The Oregonian

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I have ordered the Midway pieces suggested...sounds like the last one is really the one I need to replicate the recipe.

I have 12-15 loaded rounds that came with the rifle and match the load development, so I believe they will be exactly what the recipe calls for on other equipment. I plan to measure all of those on my equipment to take out any guesswork on differences between my equipment and his.

So i have known quantities to measure against. I am using the same bullets as the recipe for now. Once I get better at this i will develop a load on different bullets...I want to take Holland's reloading class to get hands on experience with all of this with someone looking over my shoulder.
 

Hotolds442

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Since you have loads built to recipe, and you have the recipe, why not just stick one in your press, back off the seating plug on your seating die, run the ram up, lower the seating plug to the cartridge, and lock it down. If you don't mess around with other loads for that particular caliber then it will be correct each time you screw the seating die into the press. If you're going to play around with other loads and bullets, then get a precision seating die that you can return to specific seating depths.
You could also build a dummy round to set your seating die to each time you set up to load the recipe.
 

The Oregonian

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What's important above all is understanding.
WapitiBob hit the correct approach leading to this.

The Holland tool holds no application here, and OP has no need to measure the 'bullet relationship to the lands' with a Hornady tool.
He needs only to measure his known good ammo with any CBTO comparator and log it. Doesn't matter that his numbers won't match the makers, just that he has local numbers logged, that he can reproduce from now on(a baseline).
It's simple.
CBTO absolutely can be matched with any and all components. It's 'cartridge base to ogive'.
All cases have a base, and all bullets have an ogive. As long as you use the same CBTO comparator, any one of them you happen to have, you can reproduce target CBTO -with that same comparator.

Many thanks...the above makes sense but on one point I want to make sure I clearly understand what you are saying.

I got the CBTO comparator tool. On known good ammo my tool gives about 10 hundredths longer measurement (2.5xx vs 2.6xx on my tool). I think you are saying that is fine as different tools will give different measurements than each other, but as long as it is known on YOUR own tool, you can replicate.

I believe this is bc an ogive is not a specific, universal point on various bullets. i.e. on a .308 bullet it is not as easy as saying it is the point where the radius is .306 in diameter...so each comparator will have its own version of where the ogive is.

Is that accurate?
Thx
 

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