COAL Tolerance

[topclass2017]

BACKGROUND: I have determined that for my rifle (6mmBR with an 88g Berger FB Varmint bullet) COAL should be 2.360". When loading, loaded rounds COAL typically falls within a +/- .002" tolerance. For other calibers and/or bullet combos, this tolerance is fairly consistent.

Question: What is an acceptable tolerance in COAL? Is +/- .002" too much? I am not a hardcore bench shooter, more of a casual shooter still wanting to extract as much accuracy as possible from my loads.

 

[Joe Salt]

By any change do you lube the insides of your necks?

Joe Salt

 

[dgeesaman]

I recommend you invest in a cartridge/bullet comparator tool for your dial calipers. I use a Hornady “Lock n Load” set.

Measuring to the point of the bullet is not idea for making accurate ammo.

A comparator will compare your cartridges from base to a point near the ogive of the bullet and give more useful data. This should be very close to where it engages the rifling and where the seater die contacts the bullet too.

Then if that length varies by more than .002” you can consider pursuing questions like Joe has posed.

 

[topclass2017]

I currently use a Sinclair seating depth gauge to determine the length where a particular bullet engages the rifling and go from there. I don't formally lube the inside of case necks, but there is undoubtedly lube from sizing - I use Hornady one-shot spray lube when sizing.

 

[dgeesaman]

I currently use a Sinclair seating depth gauge to determine the length where a particular bullet engages the rifling and go from there. I don't formally lube the inside of case necks, but there is undoubtedly lube from sizing - I use Hornady one-shot spray lube when sizing.

So if you’re seating bullets based on CBTO, then .004” of COAL variation is not usually important.

How far are you shooting?

David

 

[topclass2017]

thanks, David. That was the info I was looking for. I didn't figure it was an issue but thought I'd ask.

I'm generally shooting within 300 yards, though occasionally out to 600. I'd like to do some 800-1,000...but that's in the future some day.

 

[dgeesaman]

thanks, David. That was the info I was looking for. I didn't figure it was an issue but thought I'd ask.

I'm generally shooting within 300 yards, though occasionally out to 600. I'd like to do some 800-1,000...but that's in the future some day.

If you get into 800-1000, I’m told you may see some improvement from sorting the bullets by overall length, ogive length, and of course weight.

I expect that your final COALs will become commensurately more consistent as the bullet sorting sets up.

How consistent are your seated CBTOs?

David

 

[Al Lu]

"
By any change do you lube the insides of your necks?
Joe Salt"
Can you expound more please? Are you saying using lube insides of necks will increase accuracy? If yes, what lubes would you suggest? Thank you.

 

[Joe Salt]

Yes if you use a lube inside the neck,yes you will get more consistent seating depth! If you are running your bullets in a dry neck you will not get consistent seating depth. Your Galling the jacket in the brass. just like you wouldn't run you lugs without any lube would you? Or when your done cleaning your barrel and not using an oil to lube it for the first shot? I use Neco Molly

Joe Salt

 

[Evan]

Honestly COAL is only important for fitting into a magazine. Measure off the ogive somewhere with a comparator and make sure that is super consistent.

 

[DUSTY NOGGIN]

"
By any change do you lube the insides of your necks?
Joe Salt"
Can you expound more please? Are you saying using lube insides of necks will increase accuracy? If yes, what lubes would you suggest? Thank you.

i wouldnt use a wet lube or wax , and you should try an clean all that off after sizing

dry lube https://www.redding-reloading.com/online-catalog/162-imperial-dry-neck-lube-convenience-pak

if you use this , https://www.amazon.com/dp/B000Q2AM82/?tag=accuratescom-20

which i believe is mica , you might wanna read up on inhaling mica

https://www.neconos.com/item/SUPER-DELUXE-DRY-NECK-LUBE-KIT-35

 

[Straightshooter1]

"
By any change do you lube the insides of your necks?
Joe Salt"
Can you expound more please? Are you saying using lube insides of necks will increase accuracy? If yes, what lubes would you suggest? Thank you.

Using rice as a cleaning media in a vibrating tumbler will leave a light coating on the brass, which acts as a lubricant inside the neck. It works great for me where I gets less that .001 CBTO variances.

 

[K22]

I too am not a bench rest shooter but have fairly high accuracy requirements (in the 1/2 moa range) since I hunt varmints and predators at a distance.

I've noticed quite a bit of variation in bullet ogives (about .002 to .004") even with the higher priced Nosler BT's in the same lot. I haven't noticed any affect on accuracy that I can detect given my accuracy requirements that can be attributed to this variation.

My main concern is to make sure the bullet is not jammed into the land creating high pressure or a bullet stuck in the barrel when I extract a live round so I set my seating depth to about .020 to .010" from the lands there by negating the variation is bullet ogive.

 

[topclass2017]

With Bergers I am seating bullets about .010 from the lands; with various Hornady or Sierra bullets a little further off the lands (.015-.020). There is more COAL variation in HP bullets (Berger, Sierra) than in tipped as I would expect.

 

[T-shooter]

Measuring from the tip is sometimes not very accurate. These are measurements from 2 different lots of the same part number of Hornady bullets. The overall length is .015" longer on the bottom one. I used a Hornady comparator in a dial caliper to take the measurements. The insert is .010 smaller than the maximum diameter of the bullet. If you load using this tool, the jump to the lands will be much closer. But the shorter bullet has the longer ogive/nose. Even using this method, the length that is inserted into the case will vary and that will change the case capacity slightly. You can measure the distance to the lands and keep that close to the same on all loading with the same bullets.