Brass

[BD1]

        I did a weight distribution of my first lot of Starline brass last night and the results are unlike anything I've seen before. This is fully prepped brass, twice fired, resized and trimmed. It'd like there are two different distributions, with some significant outliers.  This may explain some of the flyers I've seen at times. Has anyone done a weight distribution check on a lot of Hornady Brass?  Any better?

[grayfox]

Numbers on the Pic are a little hard to read...
So, from say 111-112 grs, looks like 90% are in that, <1% delta range?
This does not sound like "2 different distributions"...
Perhaps some of our more competitive shooters will chime in.

[BD1]

    I use this same method every time. Sitting at a table I check weight the digital scale then weigh each case individually and line them up in rows. My goal is to come up with 50 cases out of 100 that are all within +/- .2 grains. Those are my match cases and I'll take the row with the most cases weighing the same and add to that from the next row until I have the 35 I need "for Score". The others from that 50 being sighters. The numbers can very depending on the structure of the match.  A typical distribution in my experience has one row that has the most matching cases, then a row either side of it with slightly fewer matching weights, and as you go out from the center the rows get shorter. Cheap brass distribution looks like a Christmas tree. High end brass distribution looks more like a Arbor Vitea tree, Like the pic I mocked up attached which is what a typical Lapua distribution has generally looked like. Using my method, (which I admit is mine alone, but it has worked for me so far), with this lot of starline 6ARC brass I have two choices, either taking the row at 11.4 grains with the rows to either side, (111.2 and 111.6 for a total of 41 cases, or taking the row at 112 grains with the rows on either side, (11.8 and 112.2), for a total of 40 cases.  I've just never seen this distribution in a single lot of brass before.
The percent range of weight is not a large number, in fact it's about what I'm used to seeing, and without the few outliers it's not something that would be very significant at 100 yards. But these are pretty small cases compared to 6.5x55 or a .308, and my goals for this rifle involve longer ranges. I guess I was expecting a more narrow range.

[StoneHendge]

Starline Brass will never be confused with Lapua. And that's before getting to the primer pockets. You get what you pay for. I'd guess that your "lot" was made with multiple "lots" of ferrules.

I haven't done it in years, but I found Hornady brass to have more outliers and deviations than almost all other brands of brass

[Tangodown]

Of all the brass I’ve used…….Hornady was the worst with the weight spread

[corpsman8483]

What accuracy bearing would brass weight have on repeatablilty, i.e. smaller groups?

[BD1]

Once you have a lot of brass fire formed to your chamber, all of the primer pockets uniformed and the flash holes uniformed, the difference in weight is directly related to the difference in case volume which is directly related to pressure, which is directly related to velocity. You are never going to get to single digit standard deviation with brass that varies much over 1% by weight in a cartridge as small as 6mm ARC.

[corpsman8483]

Let me get this straight; if I use the same pwd, same volume of pwd, and the brass has been identically prepped; you say that the brass that is > than 1% in deviation by weight, velocities will be way off (SD), than brass that is <1% of deviation by weight. Is that what you're saying?

[BD1]

Corpsman, nobody ever said anything about "way off". If you only shoot at 100 yards you'd be hard put to notice the impact variations from brass weight variations This is "down to the brass tacks" stuff. I do not sort hunting rifle brass by weight, and I do not sort Lapua brass by weight no matter it's intended use. However I do sort out the outliers in long range match brass and Lake City .556 brass. It can be the difference between low double digit SDs and single digit SDs. The availability of brass for the 6mm ARC is such that I do weigh the prepped brass and sort out anything that's more than plus/minus 1% or so from the average. The first couple humdred starline fell into two batches, the second 100 was better. For the money I'm hoping the AM brass is a significant improvement.

[corpsman8483]

Thanks for the clarification; I sort by LOADED weight. I used to weigh primers, quit that, but I do weigh the bullets I use. Recently started weighing loaded ammo and have noticed almost a 5gr difference in Starline, I don't bother weighing Hornady and use those for backyard plinking. Always weigh each pwd charge so I know I'm charging with exact amounts which only leaves the brass as a variable. I'm retired so time isn't that much of a factor. I agree that the process is really for long range shooters which I'm not ; just glad to get on paper at 100.

[CZ527 Guy]

Will be interesting when a guy does a similar observation w Alpha brass.

[BD1]

Will be interesting when a guy does a similar observation w Alpha brass.

I have some alpha brass and will do the same weight distribution observation once it has been fired twice and fully prepped. At first look it is much more consistent.

[BD1]

Sorry to be so long getting back to this. But it was a cold, windy winter day and my wife is out of town so I finally got around to doing the weight distribution on the first lot of Alpha brass. This brass is twice fired, trimmed and primer pockets uniformed. I gave the flash holes a twist just in case but there really wasn't any need as they showed no burrs or chads.  The second photo is the weight distribution of this same lot when new/unfired. Looks good, but without being prepped all it's telling us is that the pellets they start with are pretty consistent. Long story short, the Starline brass has a weight variation of 2.6 grains, while the alpha has a weight variation of 1.2 grains

[CZ527 Guy]

Mind if a guy looks for clarification on how repeatable your scale is? Not exactly questioning your results. Just based on my experience some scales are less reliable than others to s surprising degree. What scale are you using for the weight sorting?


I recently switched to an A&D FX120I balance and found it eye opening how much my previous digital scale floated around. I have never trusted a scale like Ido the A&D FX120i. Think I always suspected the float, though it was hard to accept. Since switching to the balance, float is a thing of the past.

[BD1]

Scale is a TRX-925 which reads to .01 gn. These are rounded to .1 gn or the spread wouldn't stay on the table. I live in a passive solar house with no air handling systems so there are no drafts, and the temp is very stable within any 2 hr period. So I can weigh brass pretty quickly without needing the draft shield and without needing to recalibrate very often. I have faith in it. What was your previous digital scale?

[BD1]

"I recently switched to an A&D FX120I balance and found it eye opening how much my previous digital scale floated around. I have never trusted a scale like Ido the A&D FX120i. Think I always suspected the float, though it was hard to accept. Since switching to the balance, float is a thing of the past."

What are you using for a trickier? I haven't found one I'm very happy with. Too low, or tube too short, too light weight. I just ordered the new RCBS2 to try out. All the vibratory ones I've seen are prone to clogging on stick powders and too sloppy to get to a single grain of Varget. I can do better with a manual one.  Weighing out loads is probably worth another thread on it's own.