Bullet comparator or COAL?

[JD284win]

New to the group here. Better jump in. BTO is the way to go. When I do test loads say groups of 5. I use a micrometer die. Seat them close to the chosen jump. Then measure each one BTO and adjust the last few thou as needed. Some call it over handling. For testing why not be perfect. I'll set it and forget it when I do a 200 round lot. COAL is for mag length and semi autos.

 

[one3]

Let me ask this. Once CBTO is found, then why not measure COAL.

 

[JD284win]

Let me ask this. Once CBTO is found, then why not measure COAL.

Because lots of bullets can be slightly off from the ojive to the tip. Especially polymer tipped bullets. Some bullets get fussy when they are a few thou out of desired jump. Bto is the only way to control your jump accurately.

 

[one3]

Thanks, JD284 did not realize that.

 

[PApa Black]

To me COAL has a place as a measurement if its to determine say a lenght that will fit into a magazine but as far as I am concerned there is only one true way to measure it from a reloading sense which is CBTO which is your measurement from the bolt face to the lands.

For consistent and more precise reloading you are better to measure on the ogive with a comparator

I agree w/ Aushunter1 100% !

 

[Muddyboots]

Once you start using the ogive comparator, measure the COAL (total overall case length) and see the total COAL differences due bullet total measurement differences. Go back and measure with comparator and the measurement is consistent (or should be with decent bullets). I am sure everyone agrees if you do only one thing in reloading, measure with comparator to achieve consistent jump to lands for most consistent accuracy for that load process.

Heck, if you really want to see what everyone is talking about, measure the actual bullet total length to the ogive length across a box of bullets. The ogive length will be consistent (we hope!) and the bullet length will likely vary more than anyone would like.

My reloading competency improved exponentially when I purchased the Stoney Point (now Hornady) many years ago. It is definitely a tool every reloader needs on their bench.

 

[PApa Black]

I think you're saying the same as most people here. Just some definitions or misunderstandings. My understanding of COAL is Cartridge Overall Length, the entire length base to the very tip of the bullet using just calipers and no comparator (what is the O for?). BTO or CBTO, is Cartridge Base To Ogive, using a comparator, and not measuring the Meplat or Tip of the bullet.

lightshooter: very good explanation!

 

[lancetkenyon]

G'day Greywolf
Sorry to say but where do you guys get that COAL
Is just to fit your magazine????
Coal is a measurement from the base of the cartridge to the ogive of the projectiles used in conjunction with a OAL gauge
This is used to set the projectiles within a thousand of a inch more or less for bullet jump to the lands ,
last part of loading a round getting the bullet to jump right at a given distance depends on what your rifle likes.
I don't see using the coal to get a round to fit ones mag,
it's not hard to set that by eye
Maybe go the the Hornady web site and have a read and look
At their comparator and oal gauge and inserts

COAL=Cartridge OverAll Length. From case base to tip of bullet. You use any caliper with no attachments for this measurement. With meplat differences, this number can change by .001" to .010"+ easily.


CBTO=Cartridge (or Case) Base To Ogive. You have to use a comparitor with the correct diameter to obtain this correct measurement. This measurement gives you precise numbers from bolt face to ogive of bullet, meaning consistent jump (or jam) to lands.

 

[Muddyboots]

Pictures are ALWAYS self explanatory!

 

[Mikecr]

The precision in this is not what you might think.
I challenge anyone here to calculate a 'correct diameter' for a particular ogive datum.
It's tough enough to measure or calculate an actual ogive radius. Then taking that to a land contact point on an ogive from your whatever diameter & degree of leade is not very easy.

Fortunately it doesn't matter. Land contact relationship doesn't matter. All that matters is consistent reproduction of tested best CBTO (from any local tool).
What that best CBTO amounts to ACTUALLY? Who cares..

 

[Muddyboots]

Berger Bryan Litz has a nice article explaining Effects of Cartridge Over All Length (COAL) and Cartridge Base To Ogive (CBTO ) which is attached. Nice easy read and hopefully adds info on COAL vs CBTO.

 

[bob4]

Comparator, no question. Make one that fits your mag comfortably measure ogive and go less from there.
I'm sure many like myself have found a great load then discovered...oooops doesn't fit the mag. Only did it once, that was enough to learn.

 

[Mikecr]

Did you learn to go with single shot loading?
There is no more powerful ballistic attribute than accuracy. Outside of tactical warfare, magazines add nothing for real world power.

 

[Clark]

10 12 years ago I might have been using a Sinclair bullet comparator to check length on handloads. Back when I went to the range.
Not now.
In the last 10 years I have chambered rifles with garden variety solid pilot reamers [except 223 and 6mmBR were custom reamers].
Gone big game hunting in the last 10 years with; 6mmBR, 243, 6mmRem, 250 Sav, 257 Roberts, 257 Roberts Ackley, 257 Roberts Ackley rimmed, 25-06, 260 Rem, 6.5-06, 280 Ackley, 7mmRM, 7mmSTW, and 300WinMag.

I build ~5 guns in September and leave in October, drive 900 miles, shoot and handload from my truck for a week before hunting. I work up until the primer pockets grow as shown on the extractor groove diameter change. I back off a calculated amount of powder charge for temperature and handloading variations. I do not reload. Belted brass cannot be reloaded when used this hot. I have long cartridges seated at 3.34" [never mind SAAMI COAL on 7mmRM].

Most rifles do not get used. The good ones can keep the holes in 10" target at 600 yards.