Hornady Brass Weight Variation

[StoneHendge]

I've never been a fan of Hornady brass because I've always found it to have worst in class weight variation, and weight variation equals internal case volume variation which leads to velocity variation. I now have some hard stats on a very meaningful sample to share.

A squad buddy built an ARC late last year and has been shooting Hornady factory ammo. He has been incredibly kind and given me his 1x practice brass and I get to pick up his 1x match brass. Nothing beats free brass! With 450 cases on hand (with more coming monthly) and my lot of Starline at 4x (I'll run it to 5-6x), I started to get to work on it.

I decapped and weighed about 40 pieces, tossed a few outliers out of the weight pool and came up with an average of 116.9 grains. For ease, I decided upon 116.0 to 118.0 as the weight range for my "match brass". That will be better than using Starline without sorting, and Hornady's primer pockets do seem to last a little longer then the 5-6x I get out of Starline. I segregated the >118.0 and <116.0. Seeing a lot of the lighter brass fall into 115.0 - 115.9, I further segregated that. This was the result:

>118.0              6.4%
116.0 - 118.0   73.1%
115.0 - 115.9   11.5%
<115.0             9.0%

I found it interesting that more light brass deviates from the mean than heavy, but this is probably explained by whatever process is used to make the ferrules the brass is drawn out of. I'll note that 120.0 was the max I found. 

What was most interesting was the amount of outliers on the low end. 6 pieces (1.3%) were in the 111.0 - 111.9 range. Yes one was 111.0 - that's over 5% lighter than the mean. Many more were in the 112s and 113s.

So when shooters wonder where their flyers come from, this is certainly an explanation for some. It's also an example of why more attention should be paid to SD rather then ES when analyzing load velocity variation. If you have the misfortune of having one of the outliers in your sample, its going to blow out the ES a lot more than the SD. Its also going to blow out the SD a lot more for a small sample size than a large one. You may end up ruling out a good load out of what would literally be due to "bad luck".

It will be a while, but once I develop a load for the match lot, I'll drop it in the six 111.0-111.9 cases and compare the results of those with the match lot. Who knows, maybe I'll (we'll) be pleasantly surprised by the delta. 

Assuming that the free brass keeps coming, I'll also update the pool as it gets larger.

[Santana78]

Thanks for the great info. I was breaking my head for a while there. I also had similar findings with 200 rounds of mixed Hornady Match and Black twice fired from my gas gun. My SD were all over. Once I segregated them by grain the SD greatly improved from 17-10 fps with 10 shot groups to 10 to 6 SD. I still noted some outlier ES with in them still and a lot of overlap between the 1 grain groups. I'm now trying to segregated them further into .5 grain groups and keep better track of the heavier vs lighter ones within to see if i note a difference or if it just noise from other factors I did find a high correlation between weight and volume, which I hear is not always the case with Lapua brass. I was able to get my hands on 100 peices of new Alpha brass which are all within 1.5 grains of each other. Haven't shot them yet but they're all primed already so don't want to fill them with water. I'm going to weigh and shoot them and really hoping to not find any correlation so I don't have to weigh them every time.

[grayfox]

6 Arc and 6.5 Grendel have a disadvantage in the weight/volume arena b/c they are relatively small... so a 1 gr delta translates to more % volume change than in larger, like 6.5 creed or 308 brass.

It's reasonable to find that weight delta=volume delta for a given mfr of the brass. I'd bet that hornady does their stuff in batches, and the QC is not real strict batch to batch.

The gr/vol relationship would a bit more, tenuous, when looking at 2 or more mfrs, since they can have differences in their actual mold/brass specs. Stonehenge did a study , IIRC, on this with lapua and some other 6.5 grendel brass, when looking at the specifics of the case head designs.

So far knock on wood my hdy 6 Arc brass seems, well, ok but not great, in consistency. I like starline more for that, and in 308 I have some great LC brass and some lapua's that are outstanding in consistency. At least, they are the easiest to get a good load for. I'm not in the league of Stoney or others who are shooting competitively (that would include you if you are so inclined!), just an average guy who likes to find a good load. When I get single digit SD and teen's for ES, I feel like I can take them to the field.
I am starting to break into my starline 6 Arc brass, so even these hdy's could be getting left on the shelf soon.

[mike243]

I think If I was searching ways to make my rounds more accurate I would see how much liquid they hold instead of case weight, case weight wouldn't be a accurate way to tell how much powder or dead space are in each. Maybe fine ground sand instead of water?

[grayfox]

In theory that's probably the best way. Kind of time consuming IMO unless you're in some big competition. I did that a couple times for one of my calibers.
In practice and staying within one mfr, case weight is a decent proxy. The mfr typically uses (or should use) one composition of brass, which tends to fix density and drawing characteristics, they would typically use one design structure, one set of thickness specs, one drawing/manufacturing method, case head, internal geometry, etc... so barring a great departure from those parameters, case weight, with all cases prepped the same and equal as to # of firings, can serve as a proxy. This has allowed me to narrow down my brass choices, across the calibers I shoot.

[BD1]

I think that within one lot of brass from the same manufacturer, that has been fully and consistently prepped, case weight is about as close as you are going to reasonably get. Measuring case volume in gn of H20 is something I do fairly often as it is a significant variable needed for Quickload. The issue is the meniscus. It takes some practice to find the "overflow" and then match that meniscus without going too far. And the variation from concave to max convex meniscus can easily be a grain. I typically take five or six cases of the same weight and then use the average of those case volumes in grains of water to get the value for Quickload. I can't even imagine trying to sort a couple hundred cases by water volume.
Different lots of brass, even from the same manufacturer, can vary significantly. I have sorted thousands of .223 brass over the years, and it all varies somewhat lot to lot.