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procedure for measuring case volume

 
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  #15  
Old 04-02-2012, 04:47 PM
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Re: procedure for measuring case volume

Quote:
Originally Posted by Trickymissfit View Post
I never have, but if I were to do that I would add "Photoflow." A drop of Photoflow is more than enough. I just leave the spent primer in the case. I never gave all this a lot of thought. But I did have a buddy that actually made some nylon plugs, but that was a lot of work for little gain in my book.

You can buy Photoflow at most camera shops, and a pint will last a very long time! (less than $10). It makes water seem like it it's wetter and also makes it spread out better on a surface. I use it to help me clean vinyl records, and it really helps.
gary
I checked around and couldn't find Kodak Photoflo easily.

So, I tried a few drops of Hornady One-Shot Sonic Cleaning Fluid which seems to work well.

Thanks for the pointers everyone.
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  #16  
Old 04-02-2012, 06:29 PM
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Re: procedure for measuring case volume

I've noticed that smart people complicate what they lack understanding of.
This is a comparative measure that's simple, easy, and works.
No reason to go from concerns over specific gravities(don't matter use motor oil if you want) all the way to assuming same weight cases would magically match in capacity(they don't).

The cases match in capacity as they would be used in the field, or they don't.
If you're using only new brass, then measure only new brass, every one.
If you're using fireformed brass, that's FL sized, measure that.
If you're using fireformed brass, that is minimally sized(bumped/partial neck sized), put it there & measure it.
Don't lie to yourself about the results though. You get what you got. Maybe consider all the things you can do to improve in this area.

If you want to give capacity matching highest probability, you'll hold off on any body sizing until the cases have settled closest to chamber dimension(~3rd fireforming with no body sizing). Your cases will have settled in trim length by then, and should match in trim length, or capacity checks would be useful only as a snapshot for you, and there won't ever be any real matching of it. Many case designs do not settle(like 30-06), and many do(like a 7SAUM), which is very predictable up front given that Ackley & Gibbs already explored this for us.
And of coarse your combinations of load, chamber, dies, brass quality, and other efforts, work to improve or take you from matching capacities.

There are also combinations where capacity doesn't matter as much as others. You don't even have to weigh powder for a 6PPC to shoot 'well enough'. But if I were a competitor, I would weigh powder, and my loaded case capacities would match. My bullets would be qualified, and seated exactly the same, and my loaded runout would be very low. My primers would be seated exactly(as measured), and my striking of them would be calibrated.
I would do everything I could to separate my ammo from question about performance.
I'm not a competitor, and I do this and a lot more anyway. My ammo is as good as I can make it just because it should be IMO.
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  #17  
Old 04-02-2012, 07:29 PM
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Re: procedure for measuring case volume

Mikecr -

You don't even have to be correct in your understanding of internall ballistics to shoot .25 MOA. But, I would sure like to understand more.

So, why do loaded case volume and/or case expanding to chamber volume upon ignition matter?

Is it about fuel/oxygen ratio?

And/or is it about how much gas expansion is required before propelling the bullet?

Or, other?

I realize there are meaningful ways to spend time and energy and other things that are somewhat futile. Either way, I can't see where consistency is ever a bad thing with respect to handloading and shooting.

Thanks in advance.
Richard
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  #18  
Old 04-02-2012, 09:26 PM
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Re: procedure for measuring case volume

Richard I think you hold good perspectives on this.
Capacity checks and other efforts aren't required to get guns shooting well. It might not help a bit.
But I have never found a gun that didn't take efforts to get shooting better. And many guns will never shoot good without great efforts, or blind luck.

By the time a case has expanded to chamber dimensions, we are past a significant portion of the end results. The focus and efforts in capacity matching are to address an early region of internal ballistics.

Initial confinement affects powder ignition speed(regardless of burn rate), and so it affects the pressure curve, and barrel time resulting(with most combinations).
The affects of initial confinement(before expansion to chamber) can't be considered purely as a matter of load density either, as powder with the same load density also ignites differently within different initial volumes. Any obturation that changes ignition rate is significant to most of us.

It is common for reloaders to find that MV and/or POI changes from first firing of new brass to second firing. Well, unless using one of Bart's drilled from unicorn horn barrels.. Their brass might have weighed the same, and on both firings it went to chamber dimensions, but the results were different.
You can load up cases at ~80% load density and produce 30-50fps ES through firing with powder slid back in the case on firing, to powder slid forward. This with cases perfectly matched in capacity.
Anyone who's COW fireformed can see huge differences in ignition rate and pressure based on the tamping applied, even though this component(a tissue) might seem insignificant. It's important, taking you from 'womp' to 'boom', with no change other than initial confinement.

The notons that all is taken to chamber volume regardless, is outside of this subject. Too late.
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  #19  
Old 04-02-2012, 10:51 PM
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Re: procedure for measuring case volume

Quote:
Originally Posted by Mikecr View Post
It is common for reloaders to find that MV and/or POI changes from first firing of new brass to second firing. Well, unless using one of Bart's drilled from unicorn horn barrels. Their brass might have weighed the same, and on both firings it went to chamber dimensions, but the results were different.
I've no idea where Hart got the material to make their barrels from. Four of 'em went through the same 200 WCC58 match .308 cases loaded with max charges of IMR4064 under Sierra 190's for about 1000 rounds per barrel. The other 2000 or so rounds of barrel life each was with 400 Federal nickel plated .308 cases with 41 grains of IMR4064 under Sierra 168's. All 600 cases were full length sized about 20 times. The chambers were all made with SAAMI spec'd reamers.

I didn't notice any change in accuracy for the life of each barrel. They all started out at the same accuracy level but the last 20 to 30 percent of the barrel life seemed a tiny bit less. Elevation and windage sight zeros stayed the same for each range, too. The only exception was very near the end of accurate barrel life, I had to increase elevation 3/4 to 1 MOA at the longer ranges. The throats were lengthened somewhat by then and muzzle velocity was noticably a smidgen less, evidenced by needing more sight elevation to strike point of aim.
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  #20  
Old 04-03-2012, 09:46 AM
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Join Date: Jun 2010
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Re: procedure for measuring case volume

Quote:
Originally Posted by rscott5028 View Post
I checked around and couldn't find Kodak Photoflo easily.

So, I tried a few drops of Hornady One-Shot Sonic Cleaning Fluid which seems to work well.

Thanks for the pointers everyone.
I got mine at Cord camera, but Roberts should carry it as well (both are nationwide chains). Something else that might do similar things is to mix up a solution with about two or three large drops of Dawn dish soap with a couple cups of water. Just stir it up really good and let it set till the bubbles go away.

Been meaning to touch base on the sonic cleaners now for a several months. Awhile back I was over at Harbor Freight with a buddy. They had exactly the same sonic cleaner that Lyman and the others were selling for about $30 less! Same Chinamen make all of them. Larry bought one with a couple containers of their cleaner (also cheaper), and it really does do a nice job cleaning brass.
gary
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  #21  
Old 04-03-2012, 09:56 AM
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Join Date: Jun 2010
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Re: procedure for measuring case volume

Quote:
Originally Posted by Mikecr View Post
I've noticed that smart people complicate what they lack understanding of.
This is a comparative measure that's simple, easy, and works.
No reason to go from concerns over specific gravities(don't matter use motor oil if you want) all the way to assuming same weight cases would magically match in capacity(they don't).

The cases match in capacity as they would be used in the field, or they don't.
If you're using only new brass, then measure only new brass, every one.
If you're using fireformed brass, that's FL sized, measure that.
If you're using fireformed brass, that is minimally sized(bumped/partial neck sized), put it there & measure it.
Don't lie to yourself about the results though. You get what you got. Maybe consider all the things you can do to improve in this area.

If you want to give capacity matching highest probability, you'll hold off on any body sizing until the cases have settled closest to chamber dimension(~3rd fireforming with no body sizing). Your cases will have settled in trim length by then, and should match in trim length, or capacity checks would be useful only as a snapshot for you, and there won't ever be any real matching of it. Many case designs do not settle(like 30-06), and many do(like a 7SAUM), which is very predictable up front given that Ackley & Gibbs already explored this for us.
And of coarse your combinations of load, chamber, dies, brass quality, and other efforts, work to improve or take you from matching capacities.

There are also combinations where capacity doesn't matter as much as others. You don't even have to weigh powder for a 6PPC to shoot 'well enough'. But if I were a competitor, I would weigh powder, and my loaded case capacities would match. My bullets would be qualified, and seated exactly the same, and my loaded runout would be very low. My primers would be seated exactly(as measured), and my striking of them would be calibrated.
I would do everything I could to separate my ammo from question about performance.
I'm not a competitor, and I do this and a lot more anyway. My ammo is as good as I can make it just because it should be IMO.
damn that's a good idea! Golf tees for plugs!! And they're easy to come by, and a bag should last you a lifetime. Like I said I use nothing but strait water out of the tap. Now I fill my case slightly differently that you do, in that I got my hands on a syringe that will hold enough water to do a .300 mag case (got mine at Tractor Supply). Goto a large farm supply store and they shoud have them in the large animal vet supplies. Nice thing about the syringe is that you can get different size tips for them and you start the water flow at the bottom of the case.

Len needs to start a sticky thread on reloading tips that come cheap!
gary
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