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Discussion Starter #1
hey everyone. I have read that you should measure the length of a cartridge starting at the ogive. I have a hornady bullet comparator for .308. Does anyone know the exact measurement when using hornady 168HPBT match and sierra 168HPBT both in lake city brass. Thanks for the help.
 

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A comparator is used to measure the distance from the base to some point on the bullet's ogive so that a particular seating depth can be repeated on subsequent loads, for uniformity. AFAIK, there is no standard measurement for any particular bullet, or any chamber for that matter.

Unless I am wrong. In which case, someone correct me.

Ray
 

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If you're reloading for a semi auto, you want to stick with spec COAL (like 2.800") for reliable feeding.

If reloading for a bolt action rifle, you need a Hornady OAL gauge and a modified case to test the "length to lands" (from bolt face to rifling) for your rifle then use the comparator to measure that length. Practical shooters will typically "jump" the bullet ~0.010-0.020", bench rest shooters "jam" onto the lands a few thou.

I put a few lingo terms in quotes. The major point is ... if you dont have the right tool (OAL gauge) and typr of rifle (bolt action), I definitely recommend loading to spec length. If you find yourself jammed on the lands with a hot load, the resulting pressure spike could damage your gun or worse!
 

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As raymeketa stated, there isn't any standard ogive measurement, there are too many variables and most often the tools are just comparators (meaning that they only allow you to compare your current ogive dimension against some standard that you have set the tool to).

I went through a long process trying to find a consistent tool that would provide true values and the one issue I found with most of the tools available was that they all varied by several thousandths of an inch. I settled on the Hornady tool but I made my own bushing because the original Horandy bushing is made from aluminum and I found that it changes shape and size over time which makes it impossible to be used as a direct reading tool.

Unless everyone were using the same tool with the same sized opening and all of the openings were shaped the same (some are chamferred and others have a sharp shoulder) you won't get a true comparison from one tool to another.
 

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I use the bushings from Hornady and they seem to work well and as RAMMAC has stated they are made from alum and most likely will wear down from repeated use but I am guessing they will last me for lots of reloading sessions, and to answer your question there is no exact measurement as all chambers are different so you are going to have to get a HS gage and use the bullet of choice to measure your chamber but you have to remember you will be limited by mag length.
 

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i think i know what youre getting at. is it that you want to seat your round just off the lands? to get the max length for your rifle? look at a precision mic from rcbs. that with the bullet comparator you can get the perfect length for your rifle. however, most of the time the rounds will be longer than mag length. i just load to mag length.
 

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Years ago we would just use the chamber to seat a bullet in a empty case. Put it in your seater die and adjust it down until it contacts the bullet, then give it another 1/4 turn.

Doing this with an M14, however, will give you a cartridge about 1/4" longer than the magazine can hold.
 

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My OAL/OGL for my Scout is 2.820/2.230 with a Nosler CC 168 and by bumping it out from the 2.800" I gained about 1/2" @100, this was not the only thing I did, lots of tweaks plus a tuned load
 

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Years ago we would just use the chamber to seat a bullet in a empty case. Put it in your seater die and adjust it down until it contacts the bullet, then give it another 1/4 turn.

Doing this with an M14, however, will give you a cartridge about 1/4" longer than the magazine can hold.
Pretty much what I do... Seat a bullet a little long and tweak the length back little by little until the cartridge drops out of the chamber from gravity alone. Waaaaaay easier than messing with dummy cases, lengths of rod, or that miserable hair pulling thing that comes with the RCBS Case Mic.


OP: I hail from your neck of the woods originally. Next county over, about 1mile from 53/US42.
 

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The way I do things is, after years of tinkering, I've found that more often than not a Cartridge Overall Length (COAL) of 2.82", with 168gr and heavier bullets, seems to work best for my rifles. After I verify that this is the best load I measure the ogive dimension of the assembled cartridge and record that as my standard for that combination of cartridge components and powder charge weight in that rifle. That ogive dimension will vary with different brands of the same weight bullet so I record the ogive measurement for each one.
 

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Discussion Starter #11
Sorry for the confusion on my first post. My COAL is 2.8. That's what I'm sticking with. When I measure a cartridge I get a lot of different readings. 2.84, 2.800, 2.82, 2.86 etc etc. I thought this could be bc I'm measuring from the tip of the bullet to the bottom of the case so when I did some research, I found it's better to measure a cartridge from the ogive to the bottom of the case.
When you measure from the ogive to the bottom of the case you will get a shorter measurement. My question is, using the load I have posted, what should the measurement be for a 2.8 COAL round when taking a measurement from the ogive, if anyone has ever done this. I feel kinda dumb for asking now, I just like to see every round seated to the correct depth to keep each round identical to the next
 

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I'm afraid there is no one here who can give you the number you are looking for. If you will take one of your 2.800 cartridges and measure it with your comparator, that is the number you are after. But, don't be surprised if you use that number when loading other cartridges and the OAL does not come out to 2.800". Individual meplats (points) will not be identical, even on Benchrest quality bullets. That's exactly why most competitors measure seating depth to the ogive. That's the important measurement, not the OAL.

Ray
 

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Sorry for the confusion on my first post. My COAL is 2.8. That's what I'm sticking with. When I measure a cartridge I get a lot of different readings. 2.84, 2.800, 2.82, 2.86 etc etc. I thought this could be bc I'm measuring from the tip of the bullet to the bottom of the case so when I did some research, I found it's better to measure a cartridge from the ogive to the bottom of the case.
When you measure from the ogive to the bottom of the case you will get a shorter measurement. My question is, using the load I have posted, what should the measurement be for a 2.8 COAL round when taking a measurement from the ogive, if anyone has ever done this. I feel kinda dumb for asking now, I just like to see every round seated to the correct depth to keep each round identical to the next
What you need to do is if you are comitted to the 2.800" OAL is get a bullet comparator like from Hornady and measure the ogive for that OAL with that bullet, it's impossible to give you a standard number due to the bullets design as they are all different.
 

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Here is a little information on the difference in a .308 and 7.62x51 dimensions..... Also a very nasty ammo is identified (CBC)....... haven't read all the stickies yet so I don't know if they list this stuff in them...
http://www.thegunzone.com/30cal.html
I wouldn't put a lot faith in that article, it's way off on several points but most blatant are their claim that the NATO round's maximum chamber pressure is 50,000 PSI and they also confuse their point by saying that the chamber's headspace is a major problem. And yes, McKee and Kuleck were right, there are not 7.62x51 resizing dies, only .308 Winchester so the cases are the same (within specified design tolerances).

The old Army specs of 50,000 PSI chamber pressure has been proven wrong for a long time now, that number was based on CUP units and not PSI units. The NATO 7.62x51 cartridge is in fact rated at just under 61,000 PSI and the .308 Win 62,000 PSI. For all intents and purposes they are virtually identical in the real world.

Yes, the chambers are the real difference and the military chambers are quite a bit bigger in some dimensions but the M1A as manufactured by Springfield Armory is usually chambered for a .308 Winchester so standard reloading practices apply.
 
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