Case Volume

[dr foxtail]

Obviously this topic has been beat to death but lets do it again. The data say that case volume not weight affects uniformity. I think I can get more accuracy out of my 22-250 by using more uniform cases but filling with water and then weighing and drying just sounds like a big PITA, not to mention water spilled on an expensive scale. So, better techniques with the water or different techniques altogether. Also, what is believed to be an acceptable varriance in water capacity. I could check them all and group into lots of say 1 SD.
Thanks Miles

 

[bheadboy]

brass of the same alloy in the same lot will weigh the same per reciprocal water volume, in other words, if you sort the cases of a single lot, trim to same length, then weigh the water volume will be consistant with the case weight

So trim, weigh and shoot by case weight, the water volume will be very very consistant relative to the case weight as sorted.

Bob

 

[dr foxtail]

I'm very happy to just weigh the cases, but several "studies" quoted on this forum say that case weight does not correlate with case volume. Now, that said, I could try sorting by weight and see if my groups tighten up. And, to hell with the studies. I obviously only care about what works in my gun.
Miles

 

[jlow]

Can someone point me to those studies?

 

[JohnMill]

when I was shooting pointblank the things that worked for me were to sort the brass and bullets by every available means and practice 3-4 days a week when I could. That accounted for 4 club championships and 4 of the 6 thightest aggs over a 10 year period (all since surpassed). I haven't won anything since I stopped doing all that I know you are looking for someone to tell you what works so you do not have to go through it all BUT it doesn't work like that. What really works for you are the things that you have gone through and believe in.
The hot tip is if you can't talk yourself into doing all that, the ones that do are going to be way ahead of you. And remember to have fun. If it's not fun it's not worth all that trouble.
You'll wear a barrel out learning (building a catalog of experience) so make sure you get a new, good barrel b4 an important match.
John
I just looked again and noted you did not say competition. Never mind

 

[Leaddog]

............ and practice 3-4 days a week

That folks, is the secret. If you can't get to a range, then dryfire instead. Once you have single digit SD's, the rest is up to you.

 

[lloydx2]

I would also like to see (the studies)

 

[mikecr]

brass of the same alloy in the same lot will weigh the same per reciprocal water volume, in other words, if you sort the cases of a single lot, trim to same length, then weigh the water volume will be consistant with the case weight

This is wrong.
Volume can and does stand without direct correlation to case weight.
Just measure capacity from new, to fireformed, to fully fireformed, to FL sized, and you'll see capacity changing regardless of weight.

YOU WEIGH BECAUSE IT'S EASIER

 

[Shynloco]

Guys,
More than anything, my curiosity has been raised AGAIN regarding this subject of "case volume." Now I don't compete, but love that accuracy. Thats my ultimate goal every week when I hit the range. And I know that reducing the variables to their lowest possible factors is the name of the game. But what just has never registered with me (and yes I can be THICK at times) is that if you buy Lapua brass of the same lot, and you weight it to within .5 of each other after trimming (if you even trim because I know some who compete who don't even trim and shoot lights out) and have the same bullet weight and same powder weight and their finalized and loaded cartridges weigh within .5 of each other AND you chrony them to find a low SD, what the heck does case volume have to do with anything? I'm REALLY just curious because otherwise this sounds like a bunch of opinions based on how different shooters shoot great scores and then the only truly UNCONTROLLED factor or variable is the shooter himself and the equipment used - rifle - rest or whatever they shoot off of. Given all that, I'd love to read a response. Thx guys and not trying to be think...just curiious.

 

[jlow]

brass of the same alloy in the same lot will weigh the same per reciprocal water volume, in other words, if you sort the cases of a single lot, trim to same length, then weigh the water volume will be consistant with the case weight

This is wrong.
Volume can and does stand without direct correlation to case weight.
Just measure capacity from new, to fireformed, to fully fireformed, to FL sized, and you'll see capacity changing regardless of weight.

YOU WEIGH BECAUSE IT'S EASIER

Sorry, no offence but this fails the logic test.

The question is not can you change the volume without changing weight of the case. The question is if you produce a case by a specific method and you get a weight variance, does this translate to a difference in case volume.

You can figure this out if you know exactly how they make the case but without this info, you will have to do the empirical test which is to weight he cases and check their volume and see if there is a correlation.

 

[lloydx2]

brass of the same alloy in the same lot will weigh the same per reciprocal water volume, in other words, if you sort the cases of a single lot, trim to same length, then weigh the water volume will be consistant with the case weight

This is wrong.
Volume can and does stand without direct correlation to case weight.
Just measure capacity from new, to fireformed, to fully fireformed, to FL sized, and you'll see capacity changing regardless of weight.

YOU WEIGH BECAUSE IT'S EASIER I will agree with this part of the equation. But you must think outside the box on this one. Its chamber volume that has the most effect. After all when at peak pressure that brass is almost liquid. The question is How much volume is the brass occupying in the chamber. How much room does the gas have to expand.

 

[bheadboy]

LLoyd, you miss the point, the cases fired, trimed, will have the same external size (with very little variation) you describe different case states,

take a uniform case group, fired, trimed, and then compare the water volu to carefully weighed cases that are of the same weight and the water volume will be of negligable variation.

Bob

 

[mikecr]

As initially mentioned, this has been beaten to death, yet it never matters..
Reloaders don't weigh cases INSTEAD of measuring capacity because their arms are broken. They do this, and rationalize it, merely because it's easier.
I say if you question it, do it, answer the questions.
Be sure to include a good chrono in your testing.
The pressure peak is affected by initial containment. This is capacity, neck tension, trim length to chamber end area, freebore to bullet area, bullet weight and engraving of it.
Brass weight does not directly correlate with any of these.

Also, what other shooters manage is not the same as you, so that is never a valid basis.
Someone shows up to a 1kyd line with a new gun, no break-in, no load development, new brass, borrowed load, and shoots 9 out of 10 in a group under 1/4moa. Does that mean you can? Have you considered all the factors that come into play with great shooting performance from someone, or how consistently they actually perform at that level? This happened(a bulletin here), but who was it? Did he ever shoot like that again, and was it exactly the same conditions? Did this set precedence that load development isn't needed?
A shooter could come to this board, search around a bit and conclude that zero efforts are needed to shoot like a champion, -if his basis was all the anti-effort rationalizations so dominant here. After all, no matter the specific subject, some 'great' shooter out there seemed to pay little mind to it. Right?

The question shouldn't be 'why go through the efforts'. It should be 'what might these efforts do for me',,or 'would these efforts give me an edge'.
And you should actually be more willing to find out, than to argue it away..

 

[fguffey]

and about the time someone thinks they have it figured out they find there is a difference in ‘where the brass is located’ as in a case with a thick case head and a thin case body when compared with a case with a thin case head and thick case body, both cases could weigh the same but have different different volumes, then in the same comparison, the powder column could be be long but small in diameter when compared with a powder column that is short but larger in diameter.

Then all this goes back to an article written back in the 60s, with another twist, the case powder column had to be centered, if not the case had to be indexed for repeated accuracy. The writer/shooter/reloader purchased 500 cases from the same lot from one manufacturer, he shot and culled, then went back and shot and culled and shot and culled again, out of 500 cases he settled on 60 cases + or – a few, he found faults with the cases he culled.

F. Guffey

 

[mikecr]

Good points fguffey. I forgot to include load density with initial containment factors.
And it's true that powder lie alone can greatly affect peak pressure.

A test I've done: load a round with the barrel pointed up & carefully lower to the bags before shooting. load a round with the barrel pointed down & carefully raise to the bags before shooting.
The case with powder slid rearward will show higher velocity over a chrono.
In this case, the load density nearest ignition source is higher.

Well, when a case holding a given amount of powder is smaller in volume, it's load density is higher, and MV produced is higher.
This regardless of brass weight, or chamber volume.

 

[lloydx2]

So your telling me that chamber volume doesnt effect peak pressure? You just said that freebore length does. Is this not part of overall chamber volume?

 

[mikecr]

Chamber volume affects peak pressure a great deal.
But chamber dimensions don't represent a variance.
I'm talking about the affects of containment variance as an early contributor in peak pressure, which ultimately affects barrel time of bullet travel.

Try this; Weigh some new/prepped brass to match and fire across a good chrono.
Now neck size it, reload and fire again over a chrono. Notice the velocity drop?
The brass didn't change in weight, and your chamber certainly didn't vary in volume. The only thing you changed was case volume.
This shows that brass weight and case volume do not directly correlate, and there is no math that would.

You either measure prepped & fully formed case H20 capacity, cull what departs, and control capacity with a sizing plan, or you do not actually know if your cases match.
You can be content with that, rationalize it away, but you can't deny it until you've at least measured it.

 

[lloydx2]

I agree 100% I never said that case cap doesn't affect pressure. Your putting words in my mouth. I said that chamber volume affects pressure As does case cap bullet seating depth etc.. it all works together. But you already know that. That being said If there is a weight difference in a given lot of cases It can and will change the amount of space (volume) being occupied in the chamber. Right? Regards Lloyd

 

[mikecr]

If there is a weight difference in a given lot of cases It can and will change the amount of space (volume) being occupied in the chamber. Right?

At some later(rather than earlier) part of combustion, the brass is fully obterated to the chamber, yes.
And if the primer pocket, rim thickness, and extraction groove were uniformed(along with all else), AND the brass still matched in weight, then volume at the chamber with that brass would be matching.

But I think you'll find through tests mentioned that earlier confinement/load density has already affected you more than chamber filling case weight will.

 

[diriel]

For *COMPARITIVE* ONLY Purposes, use 91% Alcohol. The reason you do this is because once you dump it out of the case it will fully evaporate quickly.

I have a 6.5x55 swede that I reload for. I have Remington, Winchester, and Lapua brass. Remington really does have a .473 head, and it is pretty consistently that measurement. Both Lapua and Winchester have a head that varies slightly more and is much closer to the .479 called for in the 6.5x55 swede case diagrams.

-- Remington = Lighter brass that has a head diameter of .473. This head diameter is pretty consistent. You can easily test this by grabbing #2 and #3 shell holders and seeing how many cases you have that fit one or the other. With Remington pretty much all of them usually fit in the standard #3

-- Lapua = Heavier brass that has a .479 type case head that varies a bit more in size than Remington does. Again you can easily test this by grabbing those #2 and #3 shell holders and seeing how many pieces fit the #2, and how many pieces fit the #3. You WILL end up with 2 groups, one much larger than the other.

-- Winchester = Heavy brass astonishingly similar to Lapua in weight and form! It has a head diameter similar to the .479 of Lapua, and you will sort cases quickly into 2 groups of #2 and #3.

I point this out because the Case Head can cause a considerable variance in weight! If you really want to sort your brass, sort by neck thickness, wall variance, and finally by Comparative Internal Capacity. Most folks say to use water, and that works great except I am a lazy, impatient bastard and don't like to wait and wait for the brass to dry. So, I use 91% Rubbing Alcohol when I am sorting by case volume. By the way, you *WILL* find that cases of the same batch will vary by internal volume enough to really mess with your ES / SD numbers.

Have a good one,
Gary