Brass weight descrepancies - how much is too much?

[Bbear]

I was gifted 100 pcs of 7mm-08 ppu brass. I had nothing better to do so I weighed them. The majority fell into 173-176 gr in weight.
My questions are:
1) for a hunting rifle, how much difference would the 3 gr difference make?

2) for a target rifle, how much difference would you accept? .1 gr? 1 gr?

 

[rfl42431]

I was gifted 100 pcs of 7mm-08 ppu brass. I had nothing better to do so I weighed them. The majority fell into 173-176 gr in weight.
My questions are:
1) for a hunting rifle, how much difference would the 3 gr difference make?

2) for a target rifle, how much difference would you accept? .1 gr? 1 gr?

For a hunting rifle, a 3 grain difference in the weight of the brass should not be very detrimental to accuracy.

For a target rifle, you'd probably want the spread to be in the 1 to 1.5 grain range. Anything outside that range can be used for short range shooting or practice.

 

[FrankG]

Your weighing brass cases. That being said......can anyone answer how much of a difference does it really make......and is the case volume more critical than the actual case weight.

A slight difference in the extractor cut on the case can easily effect the case weight but does nothing to effect case volume or performance.

So hmmmmm?

Later, Frank
Bartlein Barrels

 

[LC Tikka]

Case volume is the important part when sorting brass, even if at times there maybe correlation to weight.
Sorting by weight is a method that should have been dropped years back, its simple but inaffective.
As to acceptable discrepancy in volume, that's up to the reloader.
LC

 

[Steve Donlon]

I think it has more to do with you and your rifle than the weight of brass. I have to correct that, It does not matter to me because I have had to sort brass out of a lot 1000 pieces of SSA brass half were around 194 grs. and the other half were 174grs. Lapua has all been good enough to not worry about. I think it is more important to have the base of your bullet at the top of the powder column than a small amount of weight difference. That is where I start when I work up a load.

 

[Zero333]

You're fine.

Load and shoot.

 

[ppaul]

If you have " nothing better to do" take the five heaviest and the five lightest and check the volume of the ten cases. You'll learn something!

 

[243winxb]

I did a simple 1 time test using 100 win new brass , 243 win caliber in my Rem 40x. Brass seperated by 1/10 gr. I took 5 heavest, and 5 lightest. Shot groups with each. Then took 3 heavy & 2 light shot group. Then took 3 light & 2 heavy shot group.

Weight sorted from 100 new Win brass. Flash hole done. Lot spread about 3 grs. Batches sorted by 3/10 grs for best accuracy.

 

[GSS]

I did a simple 1 time test using 100 win new brass , 243 win caliber in my Rem 40x. Brass seperated by 1/10 gr. I took 5 heavest, and 5 lightest. Shot groups with each. Then took 3 heavy & 2 light shot group. Then took 3 light & 2 heavy shot group.

Weight sorted from 100 new Win brass. Flash hole done. Lot spread about 3 grs. Batches sorted by 3/10 grs for best accuracy.

And the results / findings were ????

 

[243winxb]

And the results / findings were ????

Flyers that opened groups were eliminated. In a 40X & Rem 600 .

Its something that needs more testing by others.

 

[corning]

I believe case volume is correlated to the case weight. The heavier weight, the lower volume, and visa versa, the lower weight the higher the volume.

My experience from when I was young and naive. I was shooting a mixed lot of un-weighed Federal brass. During the 1000 yard stage of a Palma match, I fired a round that really kicked my butt with recoil, and required assistance opening the bolt. The shot was a full 2 feet higher than any of my previous shots. I set the piece of brass aside to weigh when I got home. That piece of brass was a full 15 to 20 grains heavier than any of the other pieces of brass that I used that day. I've weighed my brass ever since.

 

[ronemus]

I did an experiment several years ago to determine just how much effect brass weight has on .223 loads. I used WW brass (sized, trimmed and deburred, primer pockets uniformed, flash holes deburred, and neck turned) , WSR primers, charges of RL-15 or N-550 powder weighed to 0.1 gr, and 75 gr A-Max bullets. Using the lightest and heaviest cases (sorted from 1000 once-fired I had on hand), I had two lots of 10 cases with a 3 gr difference in weight. The average muzzle velocity difference was 16 fps, just a bit more than the 12 fps due to 0.1 gr of powder. I choose to sort 0.5 gr lots of .223 brass for my long range loads, but the effect will only matter at 800-1000 yards - the vertical displacement on the target from such a small velocity change is negligible at shorter distances. Unless you control all other sources of variation, the effect of brass weight is negligible. I also shoot .284, and because the brass is twice as heavy I batch in 1 gr lots.

 

[Ned Ludd]

In my hands, case weight correlates quite well with case volume, something for which I have provided solid supporting data on numerous occasions. Do a search and you can find the various threads. As you'll find when reading them, there are also plenty of differing opinions here. Of course, ultimately, it's up to the user to decide what they believe and what actually works for them.

Further, it's not as simple as whether cases can be reliably sorted by weight, which is much easier and faster than determining volume. Rather, it's more likely about the fraction of the total case volume that can vary before pressure and velocity become noticeably affected. That means the specific "allowable value" in grains will vary according to case size and capacity. More likely, some percentage of the total case volume would be a more useful number across a range of different cartridge types/sizes. Although I don't think it's written in stone, I'd generally try to keep the case volume variance at or below about 0.1 to 0.5%. Keep in mind this is just general approximation based on the number of significant digits in our typical velocity values (4), and picking a comparable value in terms of case volume (i.e. using some percentage of total case volume that corresponds to the 4th decimal place or less).

Nonetheless as 243winxb mentioned above, the simplest test would be to sort cases by volume (preferably) or weight. Choose several (each) at the extreme high/low end of the range, load them up identically, then shoot them and compare velocity and grouping. If you use volume to sort the cases, I'd suggest weighing them so you can also determine for yourself whether weight sorting is a useful (and much easier) surrogate for case volume. If you can detect a difference in velocity between the highest/lowest, you should be able to decide fairly easily how much further you could subdivide brass into groups and still retain a measurable (statistically significant) output. If you cannot distinguish between highest/lowest cases in a simple test such as this, then sorting your brass is likely not going to provide any benefit.

 

[LC Tikka]

Regardless of any correlation toward case weight, it is "case volume" variations that is the unknown factor when sorting brass, so why not just measure volume up front.
If the shooting world thought about volume measuring instead of case weight the necessary tool or gauge would be on the shelf now, end of story.
LC

 

[Ned Ludd]

Have you ever tried to measure the water volume of 500 pieces of brass? No? If you had, you'd understand why sorting by weight is more desirable. Personally, I think it's pretty unlikely that an affordable tool to measure case volume would be on the shelf right now, no matter how many people wanted one. I've heard more than a few people's ideas on how to do it over the years, but those ideas never seem to pan out in the long run. Accurately and reproducibly measuring the internal volume of an irregularly-shaped object such as a brass case is not an easy thing to do inexpensively.

 

[Dud]

You might be able to use the acoustic resonance of the air inside the case to do a quick and dry measurement.

 

[searcher]

For the practical effective big-game killing range of a 7mm-08 (approx. 400 to 650 yards, roughly, and depending on bullet) you will not find any practical benefit in sorting brass when it comes to hitting a 8" vital zone. If you use it to shoot at targets, small game or small varmints at extended range, you can get a very small benefit to sorting. If most fall within that 3 grain range, as you say, I would just split them into two lots and the outliers into another for fouling shots, big-game hunting, etc. Cases differing 1 1/2 grains will have minimal discernable difference in velocity. I am a brass prep freak on target rifles - but some things make a big difference and some don't. I'd sort into 1/2 grain lots if I thought it would be worth doing.

 

[Mr.Knowit all]

Your weighing brass cases. That being said......can anyone answer how much of a difference does it really make......and is the case volume more critical than the actual case weight.

A slight difference in the extractor cut on the case can easily effect the case weight but does nothing to effect case volume or performance.

So hmmmmm?

Later, Frank
Bartlein Barrels

Outstanding points.

Once I ran out of Norma brass so I gave the Fed. brass a shot. I knew that the Federal brass was a little thick so I ran my Norma load a full grain less in the Federal brass and the Federal brass still shot faster by ~ 35 fps with less powder. This is an extreme example but same idea... inner dimensions matter when it comes to pressure. But as stated "how much?" could case thickness affect neck tension? Where does one potential problem start and the other stop? etc...
Some of these questions were considered crazy and unnecessary a few years ago but now we are shooting farther and with better accuracy from better equipment so every little piece of intel and research is or can be important.
I love the science behind it all but it can drive me crazy at times. Moderation is key.