Confused about cartridge length

[Danny Treacy]

Hi all,

I’m new to reloading bottle neck cases.

I have used the Hornady OAL gauge in my .308 bolt action rifle. The results were an overall length of 2.890” to the throat of the chamber using a bullet in the test case.

I have heard that I should seat the bullet about 5-6 thousands less than this.

This would then take the COAL to 2.884-5”.

However, when I looked at the Lyman reloading book, it states that the .308 COAL max is 2.810”.

So I’m confused as if I reduced the COAL to the max length it would reduce it in my rifle’s chamber way beyond 5-6 thou, which surely is way too much a jump to the lands?

Any information is appreciated, thanks!

 

[timbrayford]

Start at the Lyman recommendation and then increase coal incrementally, at some point you'll reach a sweet spot for consistent accuracy, powder load has a bearing on the matter too, it may take some time to get there.

 

[webley701]

Hi all,

I’m new to reloading bottle neck cases.

I have used the Hornady OAL gauge in my .308 bolt action rifle. The results were an overall length of 2.890” to the throat of the chamber using a bullet in the test case.

I have heard that I should seat the bullet about 5-6 thousands less than this.

This would then take the COAL to 2.884-5”.

However, when I looked at the Lyman reloading book, it states that the .308 COAL max is 2.810”.

So I’m confused as if I reduced the COAL to the max length it would reduce it in my rifle’s chamber way beyond 5-6 thou, which surely is way too much a jump to the lands?

Any information is appreciated, thanks!

More than 5-6 thou most certainly isn’t “way too much jump”.

If, as you say, you are new to reloading bottle necked cases, read a good reloading manual such as the Lyman one which you have (Hornady is another good one), that have extensive chapters on reloading technique including seating depth. For sporting ammunition you’ll be well advised to seat to the recommended length as shown in the load data section of a manual for the bullet in question.

Seating very close or even into the lands has its uses but for general sporting ammunition you’ll likely gain nothing you’ll be able to detect.

 

[paulst]

Yes be wary of seating into the lands for sporting ammunition, you really don’t want to leave a bullet jammed in there and powder everywhere when you try to eject an unfired round.

 

[Twodogs]

@webley701 gives sound advice, .

You say to the throat, the throat is a combination of both the freebore and the leade. The freebore being the portion of the chamber in front of the neck that has no rifling, the leade being the portion where the rifling increases from nothing to full depth. These both vary based on a number of factors.

Using the Hornady OAL system you will have identified the length of the cartridge when the ogive of the bullet contacts the leade of the rifling. This measurement is however highly dependant on how precisely you performed the measurement. This point is often referred to as ‘at the lands’ or ‘touching the lands’. It is also dependant on which bullet you use and what ogive they have.

This measurement is often referred to as CBTO, cartridge base to ogive and is far more consistent than the COAL, cartridge overall length.

The term ‘jump’ is often used, this is the distance from the point on the ogive that contacts the leade to the leade. In most cases the loaded bullet will have a jump, how much, who knows. Secant ogive bullets often prefer to be seated into the lands, I seat my 6mm target rounds 0.006” into the lands. DO NOT try this unless you know what you are doing as it can lead to increased chamber pressures amongst other things. All my hunting bullets are loaded with a jump.

Copper bullets often prefer to be seated at least 0.050” off the lands, a jump of 0.050”, sometimes much more. Some bullets will perform up to a jump of around 0.120”. A whole rabbit hole to disappear down, reloading is an art and science in its own right.

Until you are an experienced reloadeder stick with what the manuals state.

The reason manuals give an COAL, and this varies from bullet to bullet, is because they have to give a general ‘safe’ guidance when considering manufacturing tolerances and the multitude of chambering approaches and bullet styles. Also COAL is much easier to measure.

 

[M@tt]

Some bullets like a bit of jump, and if you're feeding from a magazine, that could be your limiting factor.
You can get problems if you load touching the rifling, so some jump is generally advisable.

 

[NullMac]

So I if have got this right, you have used the modified case and gauge to measure the COAL to the lands. The point of this is that it measures that dimension in YOUR rifle. So your COAL maximum in that rifle is 2.890". However the SAAMI standard COAL is 2.810" If I have got my numbers right. Most manufacturers will make the chamber a bit (sometimes a lot) longer than the SAAMI standard presumably for safety reasons. However if you know what you are doing you can use the extra length for a bit more puff, but forget that. Other people want to be precise on how far the bullet is from the lands hence they use the gauge.

I assume you are stalking.

What you never want is the bullet to get jammed in the lands by being too long, nor for cases to fail to load because they are not sized quite enough.

For field use full length resize them and load to SAAMI COAL ie 2.810". This way you know they will work.

If you have a decent set of dies the bullets will be straight and if you take care to get the powder load consistent then you will have accurate consistent rounds that do the job when you are out there.

There are years and years of bad advice still out there on the internet most of which is wrong and still repeated. So be careful about chasing accuracy (precision) as after a point it has no value in the real world. Errors from our shooting skills or wind dwarf the improvements from reloading.

I have rifles that will shoot 6mm at 100m reloading that way (probably better cos I make no claims to be a great shot nor specialist reloader.) I have tried most of the supposed genius ways to get superior accuracy and most of them are a waste of time unless you are seeking ultimate accuracy at long range and I think that's debatable as well. I have never messed about with seating depth. I know it works but if a hunting rifle shoot sub 0.5 moa just doing the above what's the point of wasting components.

My R8 shoots 7mm at 100m. That accuracy is not required, but that's what I got doing the above

Make the bullets consistently straight and a consistently accurate powder load and you will have good bullets.

Remove yourself from the shooting when testing as much as possible so you are testing the ammo not yourself.

 

[Twodogs]

As per @NullMac, consistency is key, in all aspects of shooting not just reloading.

Don’t get drawn in by peoples ‘claims’ as to dispersion or accuracy, many are based on inconsistent and statistically insignificant data.
If you want to know your rifles performance you will need to use the data from at least 20 rounds. Many measuring programmes will give you ‘mean radius’, a much better measure of your rifles potential as it uses data from every bullet not just two as in the traditional moa method.

If you are really drawn to some of the more precise aspects of reloading anything by Bryan Litz is an informative read. He is acknowledged as the bees knees of ballistics and reloading.

 

[cjm1066]

Given that a 308 can take from 110 to 200g bullets, it must have freeborn with some.

 

[Danny Treacy]

More than 5-6 thou most certainly isn’t “way too much jump”.

If, as you say, you are new to reloading bottle necked cases, read a good reloading manual such as the Lyman one which you have (Hornady is another good one), that have extensive chapters on reloading technique including seating depth. For sporting ammunition you’ll be well advised to seat to the recommended length as shown in the load data section of a manual for the bullet in question.

Seating very close or even into the lands has its uses but for general sporting ammunition you’ll likely gain nothing you’ll be able to detect.

It’s for target loads, not general sporting ammunition

 

[Danny Treacy]

Yes be wary of seating into the lands for sporting ammunition, you really don’t want to leave a bullet jammed in there and powder everywhere when you try to eject an unfired round.

Not sure why there’s an assumption that it’s ’general Sporting ammunition’ but this is for target shooting, perhaps I should have mentioned this so apologies

 

[Danny Treacy]

@webley701 gives sound advice, .

You say to the throat, the throat is a combination of both the freebore and the leade. The freebore being the portion of the chamber in front of the neck that has no rifling, the leade being the portion where the rifling increases from nothing to full depth. These both vary based on a number of factors.

Using the Hornady OAL system you will have identified the length of the cartridge when the ogive of the bullet contacts the leade of the rifling. This measurement is however highly dependant on how precisely you performed the measurement. This point is often referred to as ‘at the lands’ or ‘touching the lands’. It is also dependant on which bullet you use and what ogive they have.

This measurement is often referred to as CBTO, cartridge base to ogive and is far more consistent than the COAL, cartridge overall length.

The term ‘jump’ is often used, this is the distance from the point on the ogive that contacts the leade to the leade. In most cases the loaded bullet will have a jump, how much, who knows. Secant ogive bullets often prefer to be seated into the lands, I seat my 6mm target rounds 0.006” into the lands. DO NOT try this unless you know what you are doing as it can lead to increased chamber pressures amongst other things. All my hunting bullets are loaded with a jump.

Copper bullets often prefer to be seated at least 0.050” off the lands, a jump of 0.050”, sometimes much more. Some bullets will perform up to a jump of around 0.120”. A whole rabbit hole to disappear down, reloading is an art and science in its own right.

Until you are an experienced reloadeder stick with what the manuals state.

The reason manuals give an COAL, and this varies from bullet to bullet, is because they have to give a general ‘safe’ guidance when considering manufacturing tolerances and the multitude of chambering approaches and bullet styles. Also COAL is much easier to measure.

Thanks, this makes sense

 

[paulst]

Not sure why there’s an assumption that it’s ’general Sporting ammunition’ but this is for target shooting, perhaps I should have mentioned this so apologies

Aha, my mistake.

 

[deeangeo]

Bullet jump to lands/rifling can be as much as .040" depending on bullet type so seating depth can be adjusted until you find the sweet spot in your rifle.
Always best to start with book/manual recommendations tho'.