Weighing brass

V

VT52

Guest
Maybe interesting for some folks, old news for others... Someone at the club asked why people weigh brass and I looked up some figures to try to explain a little about the sense, or non-sense, for doing this (not just for BR, for plane-jane rec shooters as well).



Brass = 8400 kg/m3

Air = 1.29 kg/m3

Vihta N133 = 870 kg/m3


1 grain of brass displaces 1.29/8400 = 0.000153 grains of air

1 grain of brass displaces 870/8400 = 0.965 grains of powder

1 kernel of N133 weighs around 0.025grs

So 1 grain in case weight gives the same result as 0.1gr of powder (in terms of volume, not weight), ie 3-4 kernels of N133.


Depending on what you shoot (BR, plinking, high-power), that 0.1gr powder volume difference may mean nothing, or it may mean something. I can not, however (imho), see how sorting at the 0.1gr level of brass weight would mean anything, besides on paper, to real world results, as this would mean 0.01gr less volume for the powder.
 
VT52 when your shooting 1000 yards everything makes a difference, try weighing primers also, there can be a big difference. At 100- 200 not so much! Remember for every action there is a reaction in loading. One thing at a time so you know what done what.

Joe Salt
 
I don't shoot BR at 1000, only F-Class. When I'm guessing to add or drop 2 minutes of wind I don't think 0.01grs case volume will make a difference to me ;). It all depends what game you are playing.
 
Another observation to add to the mix.
Over the years, I used to start with 100 Lapua .30-06 cases to make a seasons worth of elk cartridges. As time went on, I noticed I had to start with 200 to make sure I could sort out about 80 "good ones".
One of the drivers for sorting them in the first place was that when I checked the weights, I would always find samples that you could only describe as way out of family with the batch. (More than 4 sigma away from the average.)
I used to keep them sorted out and marked them as fouling rounds. These cases were off the ends of the curve by more than 3 grains and were always found with wall thickness runouts above 0.002".
 
VT52

I started competing in 1000 yard BR last year. So my methodology is to reduce verticle to the least amount possible. My first test was to shoot weight sorted brass to determine if I can reduce ES. My conclusion to the test is the weight of each case is a small percentage of ES. Powder type, primers, seating depth, ambient temperature and a host of other ever changing variables can wreck your day. I am with Joe S. and FBecigneul I want everything as perfect as I can make it.

Eric K.
 
Would it not be more meaningful to measure inside case volume using water for this reason and measuring wall thickness for any deviation? Just weighing the brass and sorting by weight, when you don't know where that weight is, is kind of taking a lucky guess. I can imagine a case weighing the same but having a thin part and a bump somewhere where as the other case would be constant all around.

Just trying to find out the real-world benefit of weighing cases to the extreme. The point not being that it is quick to do and having piece of mind, but if there is a real tangible effect at the 0.1gr level.
 
VT52
I have been thinking about this for a while now. Being more of a tinkerer than an avid competitor
I do not shoot competition point blank, only the odd club shoot, but i do have a range at home so that helps not having to drive across state.
just making up 100 new lapua cases for my new 6PPC barrel
What i am in the process of doing and am open to criticism here.
sort by weight and mark the cases with marker pen
neck turn to thickness .270" neck so .2675"
polish neck with steel wool
uniform primer pocket, check for burrs on the inside
form a false shoulder and fireform in slave barrel with hornady butter, to give the best uniform lenght and reduce case stretch
trim to lenght
weigh again and batch into 0.5gn lots
Have not got it completed so still keen to see any weight changes occur.
JRB
 
kind of silly to weigh BEFORE brass prep.
trim to lenght does not affect effective case volume( volume below the base of the bullet), but does affect weight
neck turning does not affect case volume, but does affect weight.
primer pocket uniforming does not affect case volume( you seat the primer to the bottom of the pocket), but does affect weight.
now deburing the inner flash hole can affect case volume..but with lapua in 220 russian...very minor.

so prep then sort

you want one more sort.....???

load them all the same..this requires a lab scale, because the "close enough" of a beam or thrown charge will not cut it.

shoot in whatever string length you want..10 15.25....mark all cases that shoot OUTSIDE the mean group...use them for foulers......

mike in co
 
That may work at short range, but at long-range I would end up with zero cases in a few trips to the range :cool:
 
Mike, my 'madness' for weighing, before i started was to see if, in this case, if there was any changes in lots after the prep was completed.
You must 'speculate' which promted this experiment for me, that removing material in varing amounts from case to case, and therefore weight must ultimately effect case volume if all cases are infact uniform in every way. Unless of corse the brass varies in quality or composition, which we can rule out with the top few brass manufacturers.
My prevoius method has been as follows, happy for comment and advise
New lapua brass get 'double' what you need than weigh into two groups to split the pack, put aside any with more than 1.5 grain difference from the group for foulers and setting up etc. Share with a mate or put away for later the other half.
Do all the required prep than fire form and trim, work up a load and shoot
I have tried the cull method as you explain but not been able to repeat the results, most probably because i do not understand the process and effect.

I really like your method to cull brass, simple and effective for point blank shooting.
Can you tell us more about the peramiters you use, and whether cases get a second chance etc?
JRB
 
Last edited by a moderator:
francis,
the problem i see is the open comments...non br shooters...

they are not using lapua or the like...
they are using winchester and rem and they can infact benefit from weight sorting that stuff...


mike in co
 
Ok, so what i am seeing, if i get it right.

Top quality brass does not reqire any more sorting than just shoot it and cull?
This really helps us guys, that cannot get to the big matches and learn more.
If you guys are happy to share your brass culling method i am all ears.
regards
JRB
 
Joe Salt said:
VT52 when your shooting 1000 yards everything makes a difference, try weighing primers also, there can be a big difference. At 100- 200 not so much! Remember for every action there is a reaction in loading. One thing at a time so you know what done what.

Joe Salt
Click to expand...

Joe, I guess you are looking for more than just material weight?
what is the variable? what effect does this have low or high on bullet impact
what improvements have you seen at your distance? by sorting
What perameters do you use?
regards
Jim
 
Someone I trust once told me that a variation of 5% or more in the weight of a batch of cases or bullets indicated that a lot of culling was needed--and/or the lot might not be a good one. I took this to mean that a tolerance of 2.5% +/- was the borderline. It seems to work. I'm talking about 100 to 300 yards since this is not the long range section of the forum.
 
THE PROBELM WITH THIS IS THAT SOMEONE WOULD DO THE TEST AND CLAIM YOU WERE RIGHT......
but they would have done the powder with a thrower or a scale that is not precise, and the entire "test' was stupid do due to lack of precision.

mike in co
Zdog said:
You're right! I think the whole weighing brass thing (in short range benchrest) is a thowback to earlier days when the quality control was not as good as it is now. Even when I did weigh - I never saw anything more than 0.5-1% difference in weight, and this was out-of-the box and unprocessed. Of course if you obsess and group them by tenths (0.1gr) you can drive yourself nuts sorting them into different piles. Someone needs to make up three sets of five cases with five "light" ones, five "mean or average" ones, and five "heavy" ones and using all the same components, shoot some groups and see what happens. My prediction is there won't be enough difference between the results to measure. Of course, I could be wrong but will have to be proved so to change my mind.
Click to expand...
 
As we all know, there are a number of factors that affect uniformity of internal ballistics. It seems to me that as a practical matter we need to determine their relative importance. Unfortunately, this is not all that easy to do. Giving the constraints of time and money, most of us make the best guesses that we can, and carry on.

To test this particular thing, I think that several sets of cases would be needed, grouped by weight, and annealed (stress relieved?) so as to have more uniform bullet pull. Using weighed charges, and a chronograph, one should be able to correlate weight variation to velocity. Does anyone know of such a test?

The only one that I can think of was rather elaborately done, by the publisher of a reloading manual, to put some real numbers on the effects that changing components in a 150 gr. bullet 30-06 load. There were a series of tests done, with a pressure gun, where one component of the load was changed, and the rest were not. I wish that I could find the test. I may have thrown the manual out because I have so many, and the binding failed. In any case, one of the tests involved different brands of cases. It listed their weights, and the pressure produced with the same bullet, seating depth, powder charge, and primer. It was an interesting article. Perhaps one of you has a copy and can direct me to the source.
 
JRB said:
Ok, so what i am seeing, if i get it right.

Top quality brass does not reqire any more sorting than just shoot it and cull?
This really helps us guys, that cannot get to the big matches and learn more.
If you guys are happy to share your brass culling method i am all ears.
regards
JRB
Click to expand...

you really wanna' cull brass in a meaningful way? Chamber your guns .007 oversized at the base and look at the cases after fireforming and running thru a fitted sizer die. Keep those cases which show a concentric ring at the base.

6X47L scrub.jpg
 
JRB said:
Ok, so what i am seeing, if i get it right.

Top quality brass does not reqire any more sorting than just shoot it and cull?
This really helps us guys, that cannot get to the big matches and learn more.
If you guys are happy to share your brass culling method i am all ears.
regards
JRB
Click to expand...

you really wanna' cull brass in a meaningful way? Chamber your guns .007 oversized at the base and look at the cases after fireforming and running thru a fitted sizer die. Keep those cases which show a concentric ring at the base.

View attachment 13368


throw out those which aren't concentric

scrubbed case.jpg
 
You must log in or register to reply here.
Back
Top