Case weight vs case capacity (water weight)

[PigPknHeat]

So I have been reloading once fired LC brass separated by headstamp and have noticed that case weight doesnt always correlate to expected case capacity. For example i have found that cases of the same weight (dry) have different case capacities and some that are lighter have significantly less case capacity.

I assume this is the cause of the larger then desired SD i have seen since i am only water weight checking ranomly...

Other than checking each one with water any other suggestions for sorting for sameness?

 

[mac1911]

What type of differences are you seeing ?
Have you tried doing H2O volume measurements yet? Are you getting consistent repeat H20 weights?
How are you measuring your powder by weight or volume?

 

[PigPknHeat]

What type of differences are you seeing ?
Have you tried doing H2O volume measurements yet? Are you getting consistent repeat H20 weights?
How are you measuring your powder by weight or volume?

Cases of the same weight hold different amounts of water... and light cases hold leas water then heaveier cases...

Results arent bad i just want to be able to control as much as possible. Oiginally sorted by weight thinking would be same capacities but water volume teat proves no pattern

 

[PigPknHeat]

Lc cases tested held between 30.0gr to 31.5gr of water. Other than testing everyone there seems to be no real way to sort

 

[jtnf]

 

[76Too]

I tried checking case volume with water once...I don't think I'm smart enough to do it correctly. I measured different volumes out of the same case :/

 

[mac1911]

I tried checking case volume with water once...I don't think I'm smart enough to do it correctly. I measured different volumes out of the same case :/

exactly, I hate to get into the variables of mineral content and its effect on the water weight

 

[mac1911]

Lc cases tested held between 30.0gr to 31.5gr of water. Other than testing everyone there seems to be no real way to sort

I don't really know for sure. I did a few "water volume" test in the beginning after getting different weights in the same case I gave up. At best on a good day with my best reloads, equipment and skills I might be able to bang out 1 moa groups. So case volume is not going to be a consideration for me. Maybe if I was shooting some very high precision ammo and rifle and getting down into single digit SD might be the difference between an X or a 10 for the win at 1000 yards.

 

[gerrycaruso]

Are you and your rifle both good enough to tell the difference? If not, don't bother.

 

[PigPknHeat]

Are you and your rifle both good enough to tell the difference? If not, don't bother.

Dont know I guess but I have had great success with my 308 loads coming in at 1/2 moa with several even better but that's with lapua and nosler brass and uniform case volumes. In my ar 1 moa is about as tight as I can get it with several bullet types, and sd is in 30s and sometimes more. only ammo variable is case capacity everything else is the same.

at this point it could be other things like stock trigger and used barrel maybe 3500 reds through it... it's a chrome lined YHM

 

[mac1911]

Dont know I guess but I have had great success with my 308 loads coming in at 1/2 moa with several even better but that's with lapua and nosler brass and uniform case volumes. In my ar 1 moa is about as tight as I can get it with several bullet types, and sd is in 30s and sometimes more. only ammo variable is case capacity everything else is the same.

at this point it could be other things like stock trigger and used barrel maybe 3500 reds through it... it's a chrome lined YHM

I cant say for sure but with a SD of 30 I would think by my small mind its not case volume related? Im thinking if you where into the low teens and where trying to get better or where having ES issues?
with the small 223 case case volume will be more sensitive than say 308. So yes case volume may have an some play. Although im thinking this doesn't matter much until your looking to tighten up groups at 600 yards?

 

[NavelOfficer]

Personally, I'm happy to get all of my shots on the paper at 100 meters and iron sights.
That said, I have done simple case comparisons, but I usually use a fine powder and charge the cases just about to over-flowing. A quick glance detects any variations quite readily and accurately enough for my purposes (usually it doesn't make much difference in my shooting results). You'll see by powder height, which cases are larger or smaller volume.
You also don't get the surface tension issues like with water. Plus, you can simply empty the case and continue the reloading process.

 

[vicorjh]

FWIW, thought experiment, here are some results of changing the case capacity in tenths of a grain under simulation while keeping everything else the same. In this case, H4350 as the powder and we change the case capacity (not case weight) for 6.5 creedmoor example round:

50.230 Capacity Velocity 2702
50.330 Capacity Velocity 2699
50.430 Capacity Velocity 2696
50.530 Capacity Velocity 2694
50.630 Capacity Velocity 2691
50.730 Capacity Velocity 2689 (load 40.3 grains powder)
50.830 Capacity Velocity 2686
50.930 Capacity Velocity 2684
51.030 Capacity Velocity 2681
51.130 Capacity Velocity 2679
51.130 Capacity Velocity 2676

With everything else being the same, a case capacity variance that has even distribution across 1 grain "could" introduce ~8 fps spread within the first std. deviation and extreme spread of 26. However, there are many other variables which will contribute (not in a non-linear/additive fashion) to the actual std. dev. so whether such a distribution is relevant is hard to know. Some of the variables such as neck trim, tension, eccentricity may have a lessor or greater effect for which there are an equal number of theories and opinions. Add to that, the error in simply measuring the h2o case capacity is probably in the range of several tenths.

I'd also point out "could" since the distribution is not likely to be even and you'll end up with a better std. deviation than this example illustrates. For instance, if we have a lumpy distribution around the center,

2702
2699
2696
2694
2691
2691
2689
2689
2689
2689
2686
2686
2684
2681
2679
2676

The std. dev. in this population is closer to ~6.7. Again, keeping in mind, that this is not additive to other sources of error.


Personally, I have yet to cull brass based on either weight or capacity but will likely experiment with this in the future (am using decent brass). The items I have played with include consistent trim length, flash hole consistency, annealing the necks, neck thickness, seating depth, and runout within ~0.001. Then add consistent charge. This gets this particular load at or below ~10fps std.dev. (measured) over several dozens test rounds.

 

[PigPknHeat]

Here is my most recent OCW tests with .223/5.56. I guess i am more refering to extreme spread rather than standard deviation. Ciuple timea i didnt write down the velocity hense the gaps in data

55gr vmax
H4895
Cci41
80degF

24.0gr 2776
24.5gr 2867
24.8gr 2917
25.0gr 2873, 2917, 2943, 2930
25.2gr 2956, 2917, 2923, 2956
25.4gr 2976, 2976, 2982, 2996
25.6gr 3030, 2996, 3003, 3016
25.8gr 2996, 3016, 2982



69gr SMK
H4895
Cci41
80degF Humid

24.0gr 2699
24.4gr 2766
24.5gr 2777
24.6gr 2766, 2749
24.8gr 2795, 2807, 2812
25.0gr 2818, 2836, 2812
25.2gr 2812, 2849, 2846
25.4gr 2812, 2861, 2865

 

[mac1911]

Here is my most recent OCW tests with .223/5.56. I guess i am more refering to extreme spread rather than standard deviation. Ciuple timea i didnt write down the velocity hense the gaps in data

55gr vmax
H4895
Cci41
80degF

24.0gr 2776
24.5gr 2867
24.8gr 2917
25.0gr 2873, 2917, 2943, 2930
25.2gr 2956, 2917, 2923, 2956
25.4gr 2976, 2976, 2982, 2996
25.6gr 3030, 2996, 3003, 3016
25.8gr 2996, 3016, 2982



69gr SMK
H4895
Cci41
80degF Humid

24.0gr 2699
24.4gr 2766
24.5gr 2777
24.6gr 2766, 2749
24.8gr 2795, 2807, 2812
25.0gr 2818, 2836, 2812
25.2gr 2812, 2849, 2846
25.4gr 2812, 2861,