Brass Weight And H2O cap

truck driver · Feb 20, 2017

I weighed some once fired cases to get the H2O cap and picked out three cases that were close to being the same dry weight give or take a few tenths of a grain. Today I fired 23 rounds and cleaned them after which I decided to weigh them. I had three groups of brass with the weight being 1-2 grains difference so I measured each one to see if there was a difference in OAL which there was so I set up the case trimmer to trim to them all the same length and and reweighed some from each group to see if they would all be the same and they weren't so that blew that theory out the window.
Now I'm wondering how this will effect the accuracy?
I guess the only way to find out is to get some more H2O caps and see if there is a difference.

longrangehunter · Feb 20, 2017

To be honest at least for me, I used to hunt with my 8.59 Galaxy with the cases all the same in one box. In the end, shooter error, wrong wind call, or various other mistakes that might have come up caused more of a issue then weight sorted brass.

I certainly don't do it competing at a PRS Match. My only reason for knowing the H2O capacity is for the QL data to be more accurate. After that, the small cased 5.56/223 can show some differences out past 600 yards if using cases that are very different from one extreme to the other. The larger the case the less so IMO.

jimbires · Feb 21, 2017

Rodger , I've checked this a bunch of times , brass weight does not relate to brass capacity . the way I shoot from hunting positions I can't shoot good enough to see a difference . it might be different if I was shooting bench rest .
here are a few from my 7 rem mag , same lot rem brass

.............empty weight ...................full weight ........................capacity

#1 .........240.34 ..........................325.44...........................85.10
#2..........235.04...........................320.28...........................85.24
#3..........236.64...........................321.82...........................85.18
#4..........237.02...........................322.58...........................85.56
#5..........236.20...........................321.62...........................85.42

I only have 3 for this rifle. I misplaced my info and wanted to double check my memory .
338 Lapua , same lot Lapua brass

#1............332.62..........................449.20 .........................116.58
#2............333.54..........................449.46..........................115.92
#3............336.80..........................452.18..........................115.38

truck driver · Feb 22, 2017

Thinks for the replies. I did a little checking my self just because and these are all the same lot of Nosler seconds from SPS which is what was available at the time and may invest in some first or just buy some Norma for hunting.
First group of 3 dry weight 214.5 avg wet weight 306.7grs avg =92.2grs H2O
group 2 same lot dry weight avg 215.4grs wet weight avg 307.2 = 91.8grs H2O
group 3 same lot dry weight avg 216.7grs wet weight avg 307.1 =90.4grs H2O
This avgs out to 91.4grs H2O cap.

So after all that I see where I'm maybe .6 gr off for what I thought my h2o was for QL which I had Scotty run at 92.0grs .
How much difference will this make? After shooting loads based off the 92.0grs H2O cap the velocities in QL and my actual chronograph was only a couple fps difference.