Thread: Case weight variation powder capacity and significants on the target

My OCD kicked in today.

A few months ago I weighed 5 of each of several brands of 223 cases. Came up with an average.

As you will see the weight varies from 91.3 to 103.7 grains for the S&B (way out there) so I decided I wanted to know if there was a great difference in powder capacity for these cartridges what I did was I took five ADI cases at 94 grs and weighed them then 5 hornady cases ave 91.4.

I chose to ignore the 3 heaviest esp S&B as they do not seem to be typical.

I filled them all to the top of the neck with AR2208. In addition i used an electric tooth brush to vibrate them to settle the powder. Capacity only varied from 28.0 grs to 28.4 grs!

What are people's opinions?

Would mixing cases:

Change group size significantly?

Change point of impact significantly?

Said this many times before. Unless your hotrodding and already near max..nope bugger all at your under three hundy shooting. Under 150 I suggest you would struggle to see any difference. Take heaviest five and lightest five.load them to the same middle of road level,shoot them at hundy and see for yourself.

What you might be more likely to see, is for any given case brand and type (as they tend to have more than one machine stamping out the cases) you will see two three or more distinct groups of cases weights as you weigh up a large enough sample size.

I have been told the some makers of cases keep their cases off each machine together - the match type cases are more likely to have this done.

What I think from my limited experience playing with cases is that the volume or capacity of the case isn't so much of an issue - what I have found is the cases of different batch weights can start to behave differently in terms of not resizing properly/neck tension issues or needing annealing or maybe suffering neck cracking and the like before other batch weights in the same bunch of cases.

That's my gut feeling from my playing - I have had a batch of about 500 milsurp ex-machine gun LC 7.62mm NATO cases, and these separated out into 5 distinct groups by weight. I've used the two biggest batches, one is twice fired and on the third loading is noticeable lighter on neck tension while the other is the same but no issues and still tight. More data required on this as per but that's my observation and thoughts...

Originally Posted by No.3

What you might be more likely to see, is for any given case brand and type (as they tend to have more than one machine stamping out the cases) you will see two three or more distinct groups of cases weights as you weigh up a large enough sample size.

I have been told the some makers of cases keep their cases off each machine together - the match type cases are more likely to have this done.

What I think from my limited experience playing with cases is that the volume or capacity of the case isn't so much of an issue - what I have found is the cases of different batch weights can start to behave differently in terms of not resizing properly/neck tension issues or needing annealing or maybe suffering neck cracking and the like before other batch weights in the same bunch of cases.

That's my gut feeling from my playing - I have had a batch of about 500 milsurp ex-machine gun LC 7.62mm NATO cases, and these separated out into 5 distinct groups by weight. I've used the two biggest batches, one is twice fired and on the third loading is noticeable lighter on neck tension while the other is the same but no issues and still tight. More data required on this as per but that's my observation and thoughts...

Very interesting comments.

Originally Posted by Micky Duck

Said this many times before. Unless your hotrodding and already near max..nope bugger all at your under three hundy shooting. Under 150 I suggest you would struggle to see any difference. Take heaviest five and lightest five.load them to the same middle of road level,shoot them at hundy and see for yourself.

My thoughts too. Rare I shoot over 150yards.

Ummm, might do that test, but will be sometime ime afraid.

Originally Posted by Oldbloke

My OCD kicked in today.

A few months ago I weighed 5 of each of several brands of 223 cases. Came up with an average.

As you will see the weight varies from 91.3 to 103.7 grains for the S&B (way out there) so I decided I wanted to know if there was a great difference in powder capacity for these cartridges what I did was I took five ADI cases at 94 grs and weighed them then 5 hornady cases ave 91.4.

I chose to ignore the 3 heaviest esp S&B as they do not seem to be typical.

I filled them all to the top of the neck with AR2208. In addition i used an electric tooth brush to vibrate them to settle the powder. Capacity only varied from 28.0 grs to 28.4 grs!

What are people's opinions?

Would mixing cases:

Change group size significantly?

Change point of impact significantly?

It certainly not OCD (and I am a card carrying member of this group) to wonder how variables in components effect velocity and point of impact. Long ago I found that in my .308 I found that one additional grain of powder raised the point grain of powder raised the point of impact by around 1 inch at 100 yards. Later I found it also increased velocity by around 50 fps. Lighter projectiles also shot higher than the heavy ones. A heavier case will give more velocity than a lighter one but how much? Frankly I don't know. I have actually loaded cartridges for the .223 and .308 to test this but due to sloth are yet to shoot them. I do know from experience that results vary from cartridge to cartridge and also from rifle to rifle with the same cartridge. Will post more after shooting.
Grandpamac.

Case weight variation isn't necessarily correlated to capacity. The extractor cut and variation thereof contributes significantly

What about the effect on the brass, smaller internal capacity would equal more pressure than the larger capacity? Amounting to shorter case life or is the difference in pressure in this instance insignificant. I'm nothing close to expert or experienced enough to know. Just my thought process

I suspect there’s more to consider than just weight difference between brands as a proxy for case capacity. There maybe differences in brass composition, leading to harder or softer brass, neck tension or splitting, annealing properties, etc. The distribution of brass within the case design might also differ slightly eg thicker brass in head vs body.
I have had one example where brass weight worked out as a fairly good proxy for capacity. In 65.06ai I was working up loads for 140 AMAX with RL25. Norma brass (182-183 gn) vs RP brass (195-197gn). The RP load was giving 2920-30 fps vs Norma load at +1.5gn gave 2970fps. In both cases the load was just below max pressure as judged by ladders run previously.

If brass / case manufacturers used a standard mix across the board there may be some validity to case weight variations, but as said extractor grooves are even different, the only way to see a difference in capacity is measure cases internal volume, with a fluid that fills every part of the combustion chamber ( for that is what it is). using powder has an inherant issue in that the grains will never stack the same. Shooting at short distances will show hardly any difference its when you get past 600 yds and further you see the difference in case volume showing up as erratic velocities which at distance will show as vertical dispersion.
I suspect but have never tested if you took a Winchester case and an ADI case. That had been fired in the same rifle several times and had completely achieved their true internal volume. Then prepared them with the same charge and primer and projectile and then fired them over a chronograph or printed them on paper at distance, you would then see the difference.

My calculations using a band of 2 grains differnce in each cases capacity shows the smaller capacity case would have a higher pressure and higher velocity.
Using a .308 as my base test pressure goes from 54290 to 59600 thats over 5000 psi!! and the velocity change is a mere 40 fps so would not proove much at 100 yds but at 1000 is ? (didnt get there in calculus).

Any ways thats the difference i dont want... the extra pressure. And yes Micky I am talking about hotrod loads.
For example if I have worked up my loads in Winchester cases and then an ADI case gets in the mix now know I could expect to bump pressure up by 5000 psi, with no other variables altered.

"the only way to see a difference in capacity is measure cases internal volume, with a fluid that fills every part of the combustion chamber ( for that is what it is). using powder has an inherant issue in that the grains will never stack the same"

Perhaps this is true, I've read it many times.

But we fill cases with powder, not water so, seems more relevant to me. In any case settling the powder with a vibration will minimise any variables.

Could fill the cases for comparison of volume with a fine grain powder (which flows like water).

Originally Posted by rupert

Could fill the cases for comparison of volume with a fine grain powder (which flows like water).

Yes, I could have used AS50N which is a fairly fine shotgun powder. But, honestly, I use AS2208 in the 223 I want to know how much AS2208 they hold, not water.

If I had a container used to store biscuits and I wanted to know it's capacity, would I use water. Nope that would be useless, because of the shape and size of the biscuits. Because I need to know how many biscuits it holds. I understand it's different but, really!

Originally Posted by Oldbloke

Yes, I could have used AS50N which is a fairly fine shotgun powder. But, honestly, I use AS2208 in the 223 I want to know how much AS2208 they hold, not water.

If I had a container used to store biscuits and I wanted to know it's capacity, would I use water. Nope that would be useless, because of the shape and size of the biscuits. Because I need to know how many biscuits it holds. I understand it's different but, really!

Considering your looking for ballistic differences on target then you need to measure the metric that has the greater effect. Which is true combustion chamber size, of which the combustion gases rapidly fill and of which will then determine pressure that the projectile is subjected to.
Powder volume for the same powder will have a lesser effect than the combustion volume on pressure.

If you werent going to fire the round for an on target effect then your technique would work adequately, but still not be as good as getting a truer volume demension using a more consistent medium.

Originally Posted by johnd

..
I suspect but have never tested if you took a Winchester case and an ADI case. .....
My calculations using a band of 2 grains differnce in each cases capacity shows the smaller capacity case would have a higher pressure and higher velocity.
Using a .308 as my base test pressure goes from 54290 to 59600 thats over 5000 psi!! ..
..

That is a well known difference with older NRA shooters. Commercial Win brass had a much higher capacity than mil brass. Using the same warm load from a Win case in the mil brass would produce much higher pressure. It wasn't subtle.

As John said above, slight differences are often imperceptible on game targets out to 300yds but count for a lot past 600yds.