Case Capacity question

[tomcat818]

That is 6.5% less water volume so drop your cw by 8% and work up to the target velocity. Hypothetically, If the cw for Hornady is 41gr drop to 38gr for the Peterson and work up. If you're using common components I can run it through GRT if you provide COAL, Barrel length, already have H2O volume, bullet, powder, and distance from lands which will take you from the ballpark to the infield.

Just noticed someone mentioned dropping back 3grs and I just did the math that @memtb mentioned so all I've got is the offer to GRT it

 

[jseandsje]

The safest thing is returning to published starting loads.

I never mind.

It is not the norm, but I have found super accurate loads very near the published starting load.

You new brass needs a chance to fire form anyway.

 

[charlie 7]

OK I filled my Hornady and Petersen cases for my 6.5CM with water and weighed each one. The Hornady volume is 52.4 gr and the Petersen was 49.0 gr.
My load currently is with the Hornady brass. How should I adjust the load using the Petersen brass for same velocity and pressure? Is there a proven method to do this pr do I have to start load development from scratch?

So far we know that you measured the capacity of 2 brands of cases.
We don't know the methodology of the measuring process, further were those cases fired several times in the same chamber with neck sizing only.

As memtb mentioned earlier weight of the cases is virtually irrelevant.

 

[Ol' Red]

Crap on all that math stuff, just reduce to where you started before and work back up. It's a reason to go to the range.

 

[charlie 7]

Clem.

Very interesting, on Oct 9, 2025 you posted a thread by the same name where you measured the capacity of cases by ball powder.

Further you were aware that those cases were of different lengths, pardon the comparison but is like measuring killing capacity of an elephant gun and a pip squeak one.

In the post #10 you stated "That is the reason I used the pistol powder because of the fine granules. No settling as would be with the extruded powder."

So you used a pistol powder because of the grain size, but not all pistol powders are small grain.

Further you think that ball powder would naturally settled compact, wrong, drop tube or better still vibration would settle it more compact, just run an experiment.

 

[Clem Bronkoski]

Charlie thanks for the reminder! This time I used water. It is probably a moot point anyway because the Hornady was fired and the Petersen was new. Very likely the Hornady held more due to fire forming.
I'm just going to take the advice and start new.
I guess I posted before I thought it through

 

[memtb]

Very likely the Hornady held more due to fire forming.
I'm just going to take the advice and start new

That could be pretty significant! memtb

 

[charlie 7]

Clem.

If you want to find the usable case capacity for a given projectile and your particular seating depth of different cases, the way I would do it is as follows.

You need cases fired in your rifle several times without FL sizing, only neck sizing, deprimed and trimmed to the same length.

Clean the cases in walnut shells or better still in ultrasonic cleaner. Dry the cases.

Neck size the cases and seat the projectiles to your preferred seating depth.

You will need a platform scale for this, take a piece of plasticine the size of small walnut and weight it. Put the round on the scale with the plasticine and take down the combined weight.

Push the case projectile first in the plasticine and with syringe with a needle (in contact with the base of the projectile) slowly (no bubbles) fill the case trough the primer hole with the water to the top of the flash hole. You may use boiled previously water with a drop of dish-washing liquid.

Note the weight and with a little math you can calculate the difference in their capacities.

Well, on a second thought the exercise could be done on a normal beam scale, without the platformed one.

Hold the case in your hand while filling with water and use a tip of a bamboo skewer to plug the flash hole. If you weight the tip of the bamboo skewer and include it in your calculations you will do fine.


Calculation of a case capacity by the QuickLoad is similar to your original exercise and if your intention was to ask members for a QuickLoad data, than you may rephrase the title of the thread.

With this exercise you will be able to interpret better advice given here by other members.

 

[Turpentine21]

That could be pretty significant! memtb

Yep, all the cases I used in my little test were sized, trimmed, and ready to load. But I did seat a fired primer in each one to keep powder from exiting the flash hole

 

[Turpentine21]

Charlie thanks for the reminder! This time I used water. It is probably a moot point anyway because the Hornady was fired and the Petersen was new. Very likely the Hornady held more due to fire forming.
I'm just going to take the advice and start new.
I guess I posted before I thought it through

Try running a ladder at 300
over a chronograph watching speed, poi, and pressure. 10 or even less shots. Find the load that matches or closely approximates the speed and poi of your hornady brass loads. Next try loads just +/- and equal to the load that gave you approximately the speed of your Hornady load. Maybe .4 lower to .4 higher in .2 grain increments. .3 grain increments may work also. This time looking for consistency (ES and Sd), group size, and velocity. 3 shot groups are fine here. You can refine and tweak when you get closer to dialed in. I'll almost guarantee that you wont be far off from where you want to be. It's worth a try anyway and may save you some time and loading components.

 

[Veteran]

OK I filled my Hornady and Petersen cases for my 6.5CM with water and weighed each one. The Hornady volume is 52.4 gr and the Petersen was 49.0 gr.
My load currently is with the Hornady brass. How should I adjust the load using the Petersen brass for same velocity and pressure? Is there a proven method to do this pr do I have to start load development from scratch?

Model the two different volumes in Quickload.
It will tell you how much less powder Peterson needs to achieve the same velocity.

Then make some loads, go range and check by chrono. Proceed from there to fine tune.

 

[JustMe2]

Crap on all that math stuff, just reduce to where you started before and work back up. It's a reason to go to the range.

You beat me to it Red. Forget the math. Drop 3 grs and work your load back up. You'll need to fireform this new brass anyway which will change your pressures. I'd also recommend you do this when changing powder lot numbers, diff' powders, diff' bullets, and diff' primers.

 

[BRADMOTO]

You beat me to it Red. Forget the math. Drop 3 grs and work your load back up. You'll need to fireform this new brass anyway which will change your pressures. I'd also recommend you do this when changing powder lot numbers, diff' powders, diff' bullets, and diff' primers.

Then possibly go back up 3gr because the Peterson case handles pressures better. LOL

 

[JustMe2]

Then possibly go back up 3gr because the Peterson case handles pressures better. LOL

Anything is possible. That's why when you change a component you should start low and work back up. It's more important to be safe than sorry.