case sorting question

[Hoodlum]

I am sorting some .308 lc brass by volume.... I am filling them with water with a touch of soap for surface tension... My question is, what tolerance do you use in the groups? I have, for the majority, 55.4-56.1 gr of water, but have a few in the upper 54's and a few in the upper 56's.... Should everything in that range stay in the same group, or is the spread enough to warrant different groups?
Hoodlum

 

[George63]

I am sorting some .308 lc brass by volume.... I am filling them with water with a touch of soap for surface tension... My question is, what tolerance do you use in the groups? I have, for the majority, 55.4-56.1 gr of water, but have a few in the upper 54's and a few in the upper 56's.... Should everything in that range stay in the same group, or is the spread enough to warrant different groups?
Hoodlum

if you are going to water test, than you consider interior volume important, so why not sort

- the .7 gr spread is still more than 1% - if you divide that in thirds you have 1/2 of 1 % variance

 

[JGorski]

Hoodlum, What type of shooting will you be doing with this brass? Whatever it is, you're wasting your time, load em up and go shooting.

 

[Hoodlum]

Hoodlum, What type of shooting will you be doing with this brass? Whatever it is, you're wasting your time, load em up and go shooting.

Mainly paper hunting out to 600 for now, but working my way out farther.. What brought me to do this was when running some loads over my chrono. I was getting some pretty erratic readings... Had one 5 shot group with an ES of 255fps... I am just eliminating variables, and since I weigh each charge on a beam scale, case volume was one of my concerns... I just wasn't real sure what was considered acceptable in volume variance.... Would the volume spread of 2 gr's of water be enough to warrant the 255fps spread, or should I be looking at my chrony as the culprit? I am using a cheapo f1, but it has been pretty consistent in the past... The only variable that has changed is a new batch of brass, but from the same headstamp.
Hoodlum

 

[Skigolfmike]

That's a huge spread. Case volume may have something to do with it, but it doesn't account for that much. What is your load (powder, primer, bullet, OAL)? I have found the most important thing is consistant neck tension. I full length size every time and then trim to get consistant case lengths. You might want to check neck thickness and sort caes by that. If your beam scale is accurate to .1gr and you are on or close to an accuracy node that kid of ES should not happen.

FWIW, my ES on my 308 loads is about 15 and the SD is around 8. 24" 11.25 Krieger, 175 Berger OTM, Lapua Brass, 43.5 gr Varget, CCI 200 primer, 2.806 OAL 2720 fps.

 

[JGorski]

Mainly paper hunting out to 600 for now, but working my way out farther.. What brought me to do this was when running some loads over my chrono. I was getting some pretty erratic readings... Had one 5 shot group with an ES of 255fps... I am just eliminating variables, and since I weigh each charge on a beam scale, case volume was one of my concerns... I just wasn't real sure what was considered acceptable in volume variance.... Would the volume spread of 2 gr's of water be enough to warrant the 255fps spread, or should I be looking at my chrony as the culprit? I am using a cheapo f1, but it has been pretty consistent in the past... The only variable that has changed is a new batch of brass, but from the same headstamp.
Hoodlum

If you had your Chrony in the sunlight I'd say that was the culprit, I've had some pretty wild swings myself when mine was partially in the sun. Let's see, 255fps difference would be like 4grs of powder from one case to the next, that would be hard to do even if you had a Win and a LC case, Win holds more, LC holds less, but not 4grs. less.

 

[308boltgun]

It sounds to me like WAY to much work to test with water. Simply weighing the cases should give you the same results.

Since you will be shooting them all out of the same chamber, the available interior volume will be directly proportional to the weight of the case. Try this on some of your water sorted cases to verify the correlation and then save yourself time by just weighing the cases.

 

[George63]

It sounds to me like WAY to much work to test with water. Simply weighing the cases should give you the same results.

everyone who has carefully tested this has found it not to be true - the correlation ends at about a 3 gr spread in .308


to the OP: there is no way you will even be able to detect the difference 2gr water volume will make with that crony,

like others have said - look elsewhere to explain those readings

 

[OF&B]

Mainly paper hunting out to 600 for now, but working my way out farther.. What brought me to do this was when running some loads over my chrono. I was getting some pretty erratic readings... Had one 5 shot group with an ES of 255fps... I am just eliminating variables, and since I weigh each charge on a beam scale, case volume was one of my concerns... I just wasn't real sure what was considered acceptable in volume variance.... Would the volume spread of 2 gr's of water be enough to warrant the 255fps spread, or should I be looking at my chrony as the culprit? I am using a cheapo f1, but it has been pretty consistent in the past... The only variable that has changed is a new batch of brass, but from the same headstamp.
Hoodlum

I like to hang numbers on things to try to get a sense for when things stop mattering for what I'm doing.

1 grain of Varget with a 175 grain SMK will give a change in average velocity of 55 - 60 fps. Weighing the charge down to +- 0.1 grain cuts the contribution of powder weight to velocity spread to +-6 fps. When you weigh individual charges, you can get down to half that.

Depending on how large the chamber is and how much free bore it has, 1 grain of water volume case capacity will affect velocity the same as a quarter to half that change in powder weight.

Brass weighs 8X as much as water, so sorting sized and trimmed cases to +- 1 grain would be the same as +- 1/8 grain of water if the correlation held. Which it doesn't down to that level. But it's a huge step in the right direction and tends to equalize things like neck thickness as well.

A grain of brass is an eighth of a grain of water capacity which is a sixteenth of a grain of powder. I sort mine down to +- 1 grain lots and use the culls on both ends to set up the press and other tools.

So these things are the games played to take your SDs from teens to single digits, not the answer to train wrecks.

It's probably worth confirming the chrono.

I had a similar problem with LC01 223 brass. SDs in the 20s. Annealing dropped it down to 8 fps. Neck tension appeared to be the problem.

 

[Hoodlum]

Ok... I think I may have found part of my problem...I am shooting some new to me brass, that was bought de-primed, and sized.... I set up my dies with a fired case from my chamber and re-sized anyways before firing the brass....But, apparently the brass, or at least some of it, had excessive headspace.... I have several cases with as much as .015" headspace, and some sized down to .003", which is where I want to be.... I measured several of the cases that I had not re-sized, and the headspace was all over the place.... Some too long, and found a couple with as much as .020"..... So, this brings me to my next question.... Is there a way to stretch this brass safely? Is it safe to load some lighter charges in order to fire form this brass? ,020" just seems to be on the excessive side to be running through a fire form.... I assume that loads with that excessive amount of headspace would clearly effect velocity... Lesson learned... NEVER buy brass that someone else has had a hand in sizing!!!!!! Especially from a local show vendor that looks like he's lived in the woods for the last 10 years!!!!!
Hoodlum