Case weight and capacity: numbers heavy/technical question inside

[BigJ]

Hi guys. I'm trying to decide if separating new Lapua brass by weight is worth the effort. The gun is a 1/2MOA Rem700 308, and the application is long range competition (600, 800, and 1k yards).

600 new pieces of Lapua 308 were bought all at the same time. Sorting them by weight before any prep showed they fell into three groups:

275x 172grains
200x 173grains
125x 174grains
(grouped by whole grains, and totals rounded off to keep them easier to read)

I went ahead and prepped them all to SAAMI specs (case length = 2.005", headspaced no longer than 1.653" (several are shorter than this, but fire forming will take care of that).

Then I pulled 3 cases randomly from each group, filled them with water and weighed (using all the best practices to do so, and a GemPro 250 scale). For the three groups, the average weight of water is

172s = 54.70 grains
173s = 54.30 grains
174s = 54.58 grains

If I plug standard load numbers into QuickLOAD and only vary the "Maximum Case Capacity, overflow" value as per the above, QL tells me I can expect a whopping 9FPS difference between my three groups. Nine...

So Im wondering, WTF? Why bother keeping these groups separated by weight? Am I missing a key concept here or is my logic and reasoning sound, and combining the groups is good to go?

Thanks in advance.

[highpower790]

Unless you are better than your rifle or the ammo to be created,it really isn't worth the time.

[J-cat]

That assumes your ES is zero. If you have an ES of 9 then you're basically doubling your ES.

[BigJ]

That assumes your ES is zero. If you have an ES of 9 then you're basically doubling your ES.

Good point. Here's the ES by group for the three I pulled from each:

172s = 0.55 grains
173s = 0.30 grains
174s = 0.40 grains

And the ES across all nine cases is 0.90 grains.

How does that figure into the thinking?

[J-cat]

I'm talking about your velocity. The heavier cases will give you higher velocities.

[thomashoward]

Hi guys. I'm trying to decide if separating new Lapua brass by weight is worth the effort. The gun is a 1/2MOA Rem700 308, and the application is long range competition (600, 800, and 1k yards).

600 new pieces of Lapua 308 were bought all at the same time. Sorting them by weight before any prep showed they fell into three groups:

275x 172grains
200x 173grains
125x 174grains
(grouped by whole grains, and totals rounded off to keep them easier to read)

I went ahead and prepped them all to SAAMI specs (case length = 2.005", headspaced no longer than 1.653" (several are shorter than this, but fire forming will take care of that).

Then I pulled 3 cases randomly from each group, filled them with water and weighed (using all the best practices to do so, and a GemPro 250 scale). For the three groups, the average weight of water is

172s = 54.70 grains
173s = 54.30 grains
174s = 54.58 grains

If I plug standard load numbers into QuickLOAD and only vary the "Maximum Case Capacity, overflow" value as per the above, QL tells me I can expect a whopping 9FPS difference between my three groups. Nine...

So Im wondering, WTF? Why bother keeping these groups separated by weight? Am I missing a key concept here or is my logic and reasoning sound, and combining the groups is good to go?

Thanks in advance.

indeed,they are Lapua. Over thinking here for 9fps really?

[Metal God]

Am I missing something here ? You are talking about 2 grains total difference . I'd bet dollars to donuts there will be NO difference in anything . IMO you need a 10+gr swing before you start seeing any real recordable differences . If I bought 600 cases and the difference in weight from the heaviest to the lightest was 2gr . I'd be dancing in the streets .

If you're using IMR 4064 or the like . The gap/space between each piece of powder will differ enough though out the loaded case to make up for that 2gr difference that could just be in the head or neck of the brass and has no effect on volume anyway . You are assuming that 2gr difference is only in the case body where it could effect case volume but you really don't know where that VERY small amount of weight is at or coming from .

[hambam105]

Send me 20 pieces of Lapua Brass from each group. Then I, The Great One, will weigh each piece properly with the correct water sample with the correct Ph balance and purity. All for a small monetary donation of course.

A full written report of the findings will be sent from my people to your people in good time, naturally.

[BigJ]

I'm talking about your velocity. The heavier cases will give you higher velocities.

Right I understand. The proof will be in what we see at the range.

indeed,they are Lapua. Over thinking here for 9fps really?

Well, I didn't know it was 9FPS until all the overthinking was done .

Am I missing something here ? You are talking about 2 grains total difference . I'd bet dollars to donuts there will be NO difference in anything . IMO you need a 10+gr swing before you start seeing any real recordable differences . If I bought 600 cases and the difference in weight from the heaviest to the lightest was 2gr . I'd be dancing in the streets .

If you're using IMR 4064 or the like . The gap/space between each piece of powder will differ enough though out the loaded case to make up for that 2gr difference that could just be in the head or neck of the brass and has no effect on volume anyway . You are assuming that 2gr difference is only in the case body where it could effect case volume but you really don't know where that VERY small amount of weight is at or coming from .

Understood and agreed.

Send me 20 pieces of Lapua Brass from each group. Then I, The Great One, will weigh each piece properly with the correct water sample with the correct Ph balance and purity. All for a small monetary donation of course.

A full written report of the findings will be sent from my people to your people in good time, naturally.

Ahhh no? :P

So its sounding like the reasoning I've applied here is sound. It also sounds like I haven't missed a key factor along the way. Anyone else with experience in this area agree or disagree?

Thanks again.

[JMP]

I generally do not mix sets of Lapua and do not sort. Within each box, it tends to be very consistent.