30/06 Case Cap Trial

[Pawnee Bill]

I just finished checking the capacity of my '06 brass just out of curiosity. I checked 5 LC69 cases against 5 Lapua cases. The Lapua cases averaged 69.4 gr and the LC69 was 67.6 gr for a whopping 1.8 gr difference. Does that sound about right? I was kind of surprised at so little difference.

I used distilled water and the LC69 cases were pull downs, never fired. The Lapua cases were 4x fired. After firing the GI cases I will check them again.

 

[Uncle Ed]

When you measure case capacity according to Quickload it should be done with cases fired in "your" chamber.

That being said the larger the case and its capacity the less it will effect pressure and velocity. Meaning a smaller case like a .22 Hornet or .223 will be effected more by variations in capacity.

Example using the chart below and Quickload there was a 5,000 psi difference in chamber pressure with the same 25.0 grains of H335 between the top Lake City case at 30.6 and the bottom Lapua case at 28.0 case capacity.

 

[Wildcat455]

1.8 gr of case volume is pretty significant in my world, but your data will mean more to you after the cases are fire formed in your rifle.

For the shooting I like to do, (which is long range target and hunting) when it comes to developing loads for 30-06 and larger cases, I like to keep the volume range to .5 gr or less. I find this is easier to accomplish by keeping my case weights in same lot brass to 1 gr total per load workup. For example 30-06 case weight (with primers) 192.0-192.9.

OP, In your example of volume difference, those cases would have about a 45 fps spread and about 4,600 psi chamber pressure difference when loaded exactly the same. (Depending on powder choice of course.)

Holding the case volume to .5 gr total difference will give a variance of velocity of about 10 fps and pressure variance of about 1000 psi when otherwise loaded exactly the same (Again, depending on powder choice.)

At 1000 yards, a velocity difference of about 6 fps is about 1" of vertical. At 100 yards, you wouldn't even notice it.

For my type of shooting, I would notice a 45 fps and 4,600 psi difference.

Really, it's up to you to decide if any of this is meaningful or worthwhile to the type of shooting you do.

 

[Artisan]

1.8 gr of case volume is pretty significant in my world, but your data will mean more to you after the cases are fire formed in your rifle.

For the shooting I like to do, (which is long range target and hunting) when it comes to developing loads for 30-06 and larger cases, I like to keep the volume range to .5 gr or less. I find this is easier to accomplish by keeping my case weights in same lot brass to 1 gr total per load workup. For example 30-06 case weight (with primers) 192.0-192.9.

OP, In your example of volume difference, those cases would have about a 45 fps spread and about 4,600 psi chamber pressure difference when loaded exactly the same. (Depending on powder choice of course.)

Holding the case volume to .5 gr total difference will give a variance of velocity of about 10 fps and pressure variance of about 1000 psi when otherwise loaded exactly the same (Again, depending on powder choice.)

At 1000 yards, a velocity difference of about 6 fps is about 1" of vertical. At 100 yards, you wouldn't even notice it.

For my type of shooting, I would notice a 45 fps and 4,600 psi difference.

Really, it's up to you to decide if any of this is meaningful or worthwhile to the type of shooting you do.

Don't know if this thread will be answered or not but here goes.
I find all this knowledge very informative, essentially more to add in my vast reloading library. According to the chart above, comparing the 06 LC case, to the Lapua old stock, the less brass used, in the forming process, increases the H2O capacity of the case. Yes, No, Maybe?
Another question, without purchasing anything elaborate, what is a quick way to take an H2O reading from different cases, without getting to expensive or elaborate?
When measuring for H2O capacity, are the cases to be in their fired formed state and not resized in any way?
If there is a reply, I would like to Thank you in advance.

 

[LC Tikka]

DD
Some would say measure vol after firing, really if brass is fired in your rifle and sized with your FL die, measuring vol after sizing may also have the same consistent result.
LC

 

[Wildcat455]

Don't know if this thread will be answered or not but here goes.
I find all this knowledge very informative, essentially more to add in my vast reloading library. According to the chart above, comparing the 06 LC case, to the Lapua old stock, the less brass used, in the forming process, increases the H2O capacity of the case. Yes, No, Maybe?
Another question, without purchasing anything elaborate, what is a quick way to take an H2O reading from different cases, without getting to expensive or elaborate?
When measuring for H2O capacity, are the cases to be in their fired formed state and not resized in any way?
If there is a reply, I would like to Thank you in advance.

Donaldduck,
Yes, a heavier brass case occupies more chamber volume than a lighter brass case. Your rifle chamber volume is a fixed entity. Filling it with more brass weight leaves less volume for powder. Using a lighter case, there will be more room for powder. Heavier cases will use less powder to achieve the same pressure as lighter cases with more powder. There is a benefit to each. You may find your rifle likes heavier brass and less powder with your bullet choice, jump, barrel harmonics, powder burn rate and a multitude of other variables that come into play. Conversely, It may like the lighter case more powder etc.

To take meaningful water measurements with different brass, you first have to fire that brass in your rifle. Do not do anything to the fired case. Leave spent primer in.
This is how I do it. It's not the best method but it gets me close enough. You'll need a digital scale. I use a Hornady Lock-N-Load digital bench scale. First, weigh the fired piece of brass. Write the weight on the case with a sharpie. Fill the case to the top of the neck with water. I do this in the bathroom sink by my reloading room. I trickle the water into the case while tapping the case on the sink. This is to reduce air pockets and bubbles. I fill to the top of the neck, and try to get a water tension bubble at the top. (Looks like the case is slightly over filled with water, but not too much, just make sure it's as consistent as you can make it for all cases being compared.) I wipe the case exterior for excess water droplets and weigh the full case. Subtract the empty weight from the full weight for water fill volume weight. I write the case full weight on the case with a sharpie as well. I also record the volume weight on the case. You could do this all on a piece of paper and just number the cases. After emptying the water from the case I twist toilet paper up and twist it into the case, packing and spinning the toilet paper into the case tightly to speed drying. I also punch out the spent primer and dry the primer pocket as well, same method.

 

[Wildcat455]

DD
Some would say measure vol after firing, really if brass is fired in your rifle and sized with your FL die, measuring vol after sizing may also have the same consistent result.
LC

It'll be close, but not quite representative of your chamber volume. Some portions of the sides and bottom of the case get squeezed back to the die size, which is usually a little undersized for the cartridge. Depending on how your chamber is cut, will determine how much different it is.
I have chambers that closely match my sizing die, and I have chambers that are a little larger than my sizing die.

I believe it best to use the fired case for volume.

If you want to see where your die is resizing the case, take some steel wool, 0000 or so, and polish the case by twisting the case in a circular fashion in the steel wool prior to sizing. Be sure to lube the case prior to sizing or you'll stick it in the die. After sizing, look along the case body for shiny areas. These are the areas your die squeezed the case smaller.

 

[Zero333]

From 67.6 to 69.4 gr capacity difference is roughly 2.5 % which is no small amount...

It roughly translates close to 1.0 gr of powder difference to generate the same pressures.

 

[riflewoman]

It was well known in the 50s and 60s that military brass was heavier than commercial. The 30-06 wasn’t too bad but the 308 was very much heavier. The reason wasn’t entirely known, but the reason most often proposed was the use of the ammo in machine guns. Not only are the chambers bigger in diameter and length, but machine guns also don’t have rigid lockup. So the brass has to accept more abuse. The 30-06 was usually 10 grains heavier and the 308 was 15 grains heavier than commercial. To put it in load differences, a 308 Federal case was loaded with 42.5 Gr IMR 4895 to get a similar velocity as 41.5 of the same powder in a Lake City case.