Weight of brass

[M-61]

Separating empty brass by weight I understand. I find large deviation between different manufacturers. 308 Norma brass around 156gr and for example IMI at 181gr. These are averages. My question is given one weight to choose which would be the better choice..the heavier or the lighter brass? I have no desire to fill the cases with water to determine volume just wondered if there is a preferred case...heavier or lighter.
These are all de-primed, neck turned and cleaned.

OK if you had 10 cases of one caliber to load and two piles of brass..one heavier than the other...would you take the heavier or lighter brass?

 

[amamnn]

I don't bother to sort Norma or Lapua brass by weight any longer. It's a waste of time.

 

[gunnermhr]

I don't think it matters if you choose the light or heavy just so they're in the same sorted batch.

I've seen huge variations in Norma brass weights, sometimes up to 5 grains in 300WSM cases, this is unacceptable to me a $2 per case, I think it has to be sorted but thats just my opinion. I sure wish LAPUA would start making 300WSM brass. LAPUA can you here us guys that are using short mags??? They seem to be a cartridge that is winning and is here to stay.

 

[jlow]

It’s a good question. I am no expert but I will give you my own read on this is which is it depends on the degree of weight variation. Slight variation probably means weight sorting is not important. Intermediate weight variation for me means sorting the brass and keeping the ones close to each other in weight close together when shooting so that the translated volume variation does not affect pressure and MV. More extreme weight variations are more troublesome since not only can it affect pressure and MV but it may potentially move you out of a sweet spot depending on what weight brass you used to determine it.

Unfortunately I am not going to be able to give you specifics i.e. where the lines begins and ends for these situations – that will require some experimenting on your part.

 

[Shynloco]

Evening Chuck,
In all that I've seen, read and experienced, a key factor for me is NOT mixing brass. I'm doing something similar in which I intend to compare my usual Lapua /308 brass to some Lake City Match .308 brass I got from a friend who used LC brass in his Winchester Model 70 in FT/R competition. It's gonna be tough to outdo the Lapua brass which is within 1.5 gr of each other in 35 casings. The Lake City is like in the 3.5 grs range of each other for the same number of pcs, all having the same year head stamp. I'll be using the same loads in both brass and intend to shoot them back to back (barrel cleaning in between). You hear and read comments how brass weight variance does make a difference in outcome...guess I'm about to find out whether thats true or plain old bull.

Alex

 

[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 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. Because .308 brass is twice as heavy as .223 and has twice the volume, I would expect the effect to be halved (~6 fps for a 3 gr dfference in case weight). I would sort .308 brass into lots with a 1 gr spread in weight. Unless you control all other sources of variation, the effect of brass weight is negligible.

 

[searcher]

Between the two brands of brass, the brand that weighs the most, on average, will typically be thicker and have less case capacity. The lighter case brand being just the opposite. If case capacity in filling them is a problem as not enough room - use the lighter cases to your benefit as they should provide a bit more room. Likewise, if you have plenty of excess capacity after filling the case - you might opt for the heavier case to bring the powder level up closer to a fill situation, resulting in more uniform pressures.

If case capacity is not an issue, divide your weighed cases into lots and you will probably be rewarded with less vertical stringing, at the least.

I would suggest doing "final" load development with both brands after you have found a few promising loads with either brand. You may find that one brand just doesn't work well - no matter they are weight sorted.

 

[CatShooter]

Between the two brands of brass, the brand that weighs the most, on average, will typically be thicker and have less case capacity. The lighter case brand being just the opposite. If case capacity in filling them is a problem as not enough room - use the lighter cases to your benefit as they should provide a bit more room. Likewise, if you have plenty of excess capacity after filling the case - you might opt for the heavier case to bring the powder level up closer to a fill situation, resulting in more uniform pressures.

If case capacity is not an issue, divide your weighed cases into lots and you will probably be rewarded with less vertical stringing, at the least.

I would suggest doing "final" load development with both brands after you have found a few promising loads with either brand. You may find that one brand just doesn't work well - no matter they are weight sorted.

The difference in weight may be enough to effect vertical stringing at long ranges, but it is NOT enough to effect the fill volume of a case. If you take 308 cases of 165gr and 175gr respectively, and load them with 44gr of your favorite brew, you will not see any difference in volume.

The "apparent" fill volume is more effected by the amount of FL sizing, and the state of anneal, which effects the apparent volume, but not the firing volume.

 

[searcher]

Regarding Catshooter - perhaps he has never used different brands of brass or seen the differences between military brass... Dead wrong on that one - though he does pose other interesting bits.

 

[CatShooter]

Regarding Catshooter - perhaps he has never used different brands of brass or seen the differences between military brass... Dead wrong on that one - though he does pose other interesting bits.

I have used different kinds of brass - the fill level is more determined by the way the powder is dropped into the case, than the weight of the case. A lot of commercial cases weigh as much or more than military cases...

 

[mikecr]

I agree with catshooter in that it would be hard to assume powder case fill correlations with brass weight.
10gr diff in brass weight, which is heavier than powder weight, and spread over undetermined areas case to case, could not be said to mean anything without actual measure(h20 capacity).
While anyone should know better than to mix different brass, choosing cases based on weight rather than capacity is more an act of faith than logic. It very well could be detrimental.

I don't agree with implications that generalize volume, as I see no difficulty in just measuring it.
I also know that initial volume(not 'apparent') affects tune and ES, as it affects the pressure curve peak. And, we can size same weighing cases to significantly differing volumes. This alone invalidates weight -vs- capacity correlation.

To see it, match 10 fireformed and unsized cases by both H20 capacity and weight.
Now FL size 5 of them and remeasure their capacities. You'll see it drop, and variance in it rises.
Now load & fire them across a chrono round robin. You'll see slightly higher MV and ES from the FL sized cases.
But they all weigh the same..

 

[CatShooter]

I agree with catshooter in that it would be hard to assume powder case fill correlations with brass weight.
10gr diff in brass weight, which is heavier than powder weight, and spread over undetermined areas case to case, could not be said to mean anything without actual measure(h20 capacity).
While anyone should know better than to mix different brass, choosing cases based on weight rather than capacity is more an act of faith than logic. It very well could be detrimental.

I don't agree with implications that generalize volume, as I see no difficulty in just measuring it.
I also know that initial volume(not 'apparent') affects tune and ES, as it affects the pressure curve peak. And, we can size same weighing cases to significantly differing volumes. This alone invalidates weight -vs- capacity correlation.

To see it, match 10 fireformed and unsized cases by both H20 capacity and weight.
Now FL size 5 of them and remeasure their capacities. You'll see it drop, and variance in it rises.
Now load & fire them across a chrono round robin. You'll see slightly higher MV and ES from the FL sized cases.
But they all weigh the same..

Well said - most people that argue about case weight have never considered that the "apparent" volume of cases changes with when you measure it.

The only true measure of the volume is the weight - since brass has a fixed specific gravity, then 175 grains must take up the same space - the only possible variable in the extractor cut (which I have found is pretty consistent). The true determinant of case volume, is when the case is under pressure in the chamber... and in the end, that is the only volume that counts.

 

[mikecr]

The only true measure of the volume is the weight - since brass has a fixed specific gravity, then 175 grains must take up the same space - the only possible variable in the extractor cut (which I have found is pretty consistent). The true determinant of case volume, is when the case is under pressure in the chamber... and in the end, that is the only volume that counts.

I don't agree at all. Initial confinement IS significant to outcome.
Dismissing this would be like dismissing bullet grip of necks, or load density, and there is no way to do it. By the time a case fully obturates to a chamber the affects of these things have already mattered.
But all the thickness of a case against chamber walls matters at that point, is with expansion ratio as an immeasurable variance.

Now anyone who has measured H20 capacities learns, or should have, that it does not correlate directly with case weight. To match capacity you have to get cases to the same INTERNAL DIMENSIONS, and weight does not show this. So by culling cases different by ~10gr or so, someone doing this may actually be mis-matching batch capacities.

To get H20 capacities, you must fully fireform cases -without sizing, and then measure.
From this stable point you can best match cases, and depending on lot(not brand), they may or may not weigh the same. But you'll never know capacities until measured anyway.

 

[Shynloco]

At the risk of sounding very simplistic and certainly appreciating all the technical and obviously knowledgeable folks and their dialogue regarding the pros and cons of case weight, case capacities and so on (most of which my little brain has problems fully understanding the virtues thereof), it strikes me that the original question posed was whether to choose the lighter or the heavier brass groups. What I've found is that I separate each manufacturer's brass (that I intend to shoot) by case weight and then load and shoot that brass to see which group or manufacturers' brass works the best in my particular rifle at whatever distance I intend to shoot. Perhaps I'm being too "simple minded" about this, but best accuracy is REALLY all I care about. I'm not sure knowing what the internal capacities or even case weight will help my rifle shoot better. It'll be her call in the end anyways as to whether she likes the lights or the portly casings.

Alex

 

[mikecr]

Now that makes sense Alex.
Even with measured and matching capacities, cases of different lots can respond differently as sized, chambered, fired, and extracting.
It could be that heavier lots include more thickness variance, causing bowing runout. Neck tension changes with thickness. Different thickness in webs may mean different flash holes or primer pockets, or extraction issues early to later. Shoulder bumps set differently.

Much as we match these things, it shows if nothing else that cases have character that sometimes follows lot, and surely brand.