Brass volume

dannySLO · Rookie Member Joined: Jan 21, 2009 Posts: 11

Hello,

I weight specimen of my .308 win brass, fill up with wather.

The results are (in grain):
- 229.8
- 229.0
- 229.0
- 228.9
- 228.7
- 228.7
- 228.6
- 228.4
- 228.3
- 228.2
- 228.2
- 228.1
- 227.7

I need advice, how big can be deviation in volume for good varmint shooting up to 600 meters (I use Sierra 168 gr. HPBT match bullets)? Of course as soon as possible, but anyway what is rational limit....

Best regards,

Danny

gelandangan · Posted: Mon Aug 17, 2009 2:08 am Post subject: Re: Brass volume

Hi just to ensure we are in the same track,

most of my 308 winchester cases can only load up to about 56 grains of water
so what is the trick you use to load up over 4 times of mine?

Just to compare,
a 300 Win Magnum can load to 88 grains of water.
a 45-70 Govt loads 79 grains
a 500 Nitro Express 3" loads up 138 grains
YOUR .308 WIN loads up 228 grains!!!!!!!!!!!!!!!!!!!!!!!!!!!!! Shocked

a 50 BMG loads 300 grains

chambered221 · Posted: Mon Aug 17, 2009 4:41 am Post subject: Re: Brass volume

A 1 grain deviation is somewhat the standard for weight sorting!!!
No need to do it with water though.
If using electronic scale weigh each and segregate by one grain difference.
If using a balance beam, weigh enough cases to get an average, set your scale at .5 grain below the average, anything that weighs below goes in one pile anything above that in another pile.
Then set scale .5 grain above the average, take the pile that weighed above in last sorting and place back on the scale to find those that are above that setting and make a third pile.
When done you should end up with about 75-80 % of your brass in one group that will weigh within 1 grain of each other.
This process will take a lot less time than weighing each individual case on a beam scale.

skb2706 · Member Joined: Apr 10, 2006 Posts: 269

Your brass must be somethin real special. Assuming you are correct, but we know its not possible, you are less than 1% variation. With the brass that I've weighed over many years of doing this.......yours is as close as any I've seen.
For shooting varmints in volume I wouldn't sweat it anyway.

Pumpkinslinger · Posted: Mon Aug 17, 2009 7:22 am Post subject: Re: Brass volume

I'm guessing this is the case plus water weight. I weighed a .260 Rem case (necked down .308 Win) and got 165 grains or so. Add 56 grains of water and we're at 221 grains...

dannySLO · Rookie Member Joined: Jan 21, 2009 Posts: 11

Sorry, in hurry I put case plus water weight.

Correct wather volume data are:
- 57.2
- 57.0
- 56.9 2 times
- 56.8 2 times
- 56.6 2 times
- 56.5 3 times
- 56.4
- 56.3

Thanks chambered221 for suggestin.

Regards, Danny

Grumulkin · Posted: Mon Aug 17, 2009 2:31 pm Post subject: Re: Brass volume

A fun thing about handloading is experimentation.

Why don't you sort your cases into a set with only plus or minus up to 0.1 weight variation and then reload that and also reload a set of unsorted brass. Then test at 600 yards. I'm thinking there will be no significant difference on paper but, let us know your results.

Pumpkinslinger · Posted: Mon Aug 17, 2009 2:34 pm Post subject: Re: Brass volume

I personally wouldn't worry about that much variation.

dannySLO · Rookie Member Joined: Jan 21, 2009 Posts: 11

Grumulkin wrote:

A fun thing about handloading is experimentation.

Why don't you sort your cases into a set with only plus or minus up to 0.1 weight variation and then reload that and also reload a set of unsorted brass. Then test at 600 yards. I'm thinking there will be no significant difference on paper but, let us know your results.

Sort into a set with only +/- 0.1 grain weight variation means too many sets with a little casses... First I'll try with +/- 0.5 grain and I'll see, how that reflect on 100 meters shoting group.

Best regards,

Danny

fnuser · Posted: Mon Aug 17, 2009 4:30 pm Post subject: Re: Brass volume

water is a tricky thing, sometimes surface tension allows different appearing weights even in same case, also if there is a spent primer in the pocket an air bubble can be present which will allow less water. I've tried plugging them with toothpicks but this doesn't work much better. if you neck turn you would think that you are uniforming the case but again this isn't always the case, no pun intended. some different weight cases may have identical volumes, depending on wall thickness, concentricy etc. The only sure-fire way I've found is to shoot the cases with a known good load and cull the fliers outside of your acceptable standard.

fnuser · Posted: Mon Aug 17, 2009 4:32 pm Post subject: Re: Brass volume

Pumpkin's probably right so depending on your state of sanity pick one.

gelandangan · Posted: Mon Aug 17, 2009 5:28 pm Post subject: Re: Brass volume

Just to lay some ground info,

The below is only a theoretical calculation made by using a computer program,
which may be a very dangerous load on your gun.
Please do not use the loads below.

Assumptions:
1. Powder used = Varget (ADI AR2208)
2. OAL = 2.8 inch
3. Projectile used = .308, 168, SRA HPBT MatchK 2200
4. Load density 100%

At highest volume of 57.2 grains of water (46.27 gn of powder) chamber pressure is 65000 psi
at lowest volume of 56.3 gn of water (45.44 gn of powder) pressure = 58981 psi

=================================================
Now using MY load, I use 43.5 gn of Varget for the same projectile,

the larger volume case (57.2gn) would fill 94% of the case and work at a comfortable pressure of 49800psi (giving a theoretical 2759 fps)
the lower volume case (56.3gn) would fill 95.7% of the case and the pressure goes up to 51600psi (giving a theoretical 2777 fps)

You can see that the pressure does differs to about 2000 psi or 4%.
But the MV variation is only about 20fps.

Would that make any difference? beats me...
if you are splitting lines in paper target.. yeah, maybe you can go anal and sort out your case weight.
On the other hand, varmint shots, hmm.. your variables stacks up higher, temperature, pressure, wind, sunlights, dust, elevation, type of animal, etc etc etc..

Bugger mate, just use the case and dont waste time worrying about the miniscule differences.
Enjoy your hunt!! Very Happy

Handloader · Posted: Mon Aug 17, 2009 5:39 pm Post subject: Re: Brass volume

For me, weighing cases is mainly to determine if there is a significant difference. Some cases can weigh as much or as little as 8% off average; these become the cases used for fouling and sighting in.

Whether varminting or hunting, accuracy depends, as well all know, on consistency. While that includes case weight, variations of + or - one grain from average seem to have very little affect on accuracy. More critical by far is bullet runout and here we find a major affect on accuracy when runouts exceed .002" or less. Another example is weighed powder charges.

While we may really feel good about weighing each and every charge, that, too, is seldom a signficant factor in attaining top accuracy. Powder charges can be assigned by volume or by weight (a specific volume being equal to a specific weight). Observe bench rest shooters at a registered match reloading their cases and you not find but a few that actually weigh the powder charge. Of course, they have some sophisticated powder measures, but, if one owns a powder measure capable of throwing to + or - one tenth of a grain, there will be no affect on accuracy or on SD for that matter. If using a measure with a big hopper, keep the powder level reasonably consistent as that will keep charge density consistent.

Like most here, I will expend the needed effort to craft good quality consistent ammo. It gives a modicum of confidence in our loads when we see those nice small groups. But, that said, if we are striving for accuracy at long range other critical factors dominate (mirage and wind as well as knowing the exact distance, and, if we get really into it, knowing the humidity, elevation and temperature). For many, the bigger and more productive challenge is learning to shoot accurately at extended ranges and, like most shooting endeavors, is a product of practice, extensive practice. In that regard, a perfect handload may give only the slightest of advantages relative to knowing how to shoot that specific handload.

chambered221 · Posted: Mon Aug 17, 2009 6:35 pm Post subject: Re: Brass volume

Danny, I seriously doubt you’ll see anything at 100 meters with cases that have 2-3 grains weight difference.
If 600 meters is your defining distance I recommend testing at that distance to gain a true evaluation of your expectations.

I do weigh cases on a beam as previously described only to rid the group of any really off par cases that may be present.
In the past I have found cases +/- 5-8 grains from the standard group.

Dawgdad · Posted: Wed Aug 19, 2009 6:07 am Post subject: Re: Brass volume

Danny
you are trying to do two things at once an need to separate the steps.

If you take the empty brass by weight first. no water. Then fill them with water and subtract the brass weight of that case - you get a weight of water equal to the volume of the case. The internal dimension of the brass is what you are trying to keep uniform so that the internal ballistics will be as uniform as possible to give you uniform external ballistic results.

Okay now I read the rest of the post.... you have a very tight set of results.

Your 13 cases have a SD of .26 and a percent relative standard deviation of 0.4%.... that is very good. If you take on SD either side of the mean value of 56.7 you would include all but the high and low case.

So throw out the 57.2 and the 56.3 and have a set of 11 cases that will be more uniform than you can hold the gun steady.

57.2
57.0
56.9
56.9
56.8
56.8
56.6
56.6
56.5
56.5
56.5
56.4
56.3
56.7 avg
0.26 SD
0.46 %RSD

57.0 avg+1sd
56.4 avg-1sd