Can case volume be inferred by its weight ?

[ajvanwyk]

OFF-TOPIC:

As a benchmark, small sample as it might be...

For the most recent National State Teams, every shooter in the Victorian team was shooting 7mm SAUM. 3 in 5 shooters used Sierra 183gn and the other 2 used Bergers 1x VLD and 1x Hybrids. We did a significant amount of work leading up to the match in WA and the one stat that I had a quick look at was that every shooter had an SD below 5 and ES below 14. These measurements was taken during training using a Labradar shooting 15+2 shot strings. I would say that's a pretty good sample, even though only 1 team... although they were the Champions

Resized_IMG_8284.jpeg

Scope Zeroing at 300yd...
Not relevant for this discussion, but I love the photo

[Gyro]

Very interesting and clearly a diversion to the present discussion but at one of the big Oz shoots not so long back it was asked of the shooters to maybe supply thier load details and a few top F Open guys did and thier ES numbers were not in single digits. One of your top guys if I remember correctly was well into double figures. This is a diversion but surely most of us know that a lot of other things are going on ( like what happenss in a 30" barrel ) that have no bearing on the volume of the pressure vessel, in this discussion the cartridge case.

[UL1700]

With the extreme accuracy achieved with modern presses (I may have accidentally ordered a Heavy Präzipress ) and dies, has anyone ever tried compensating for case volume with seating depth or indeed are these relatively tiny variations in case volume completely negated by varying bullet dimensions or as the bullet is ejected from the case on ignition does the seating depth have little to no relevance with relation to case pressure I think I need to change my motivational office desktop background... or get hold of a pressure trace

20181209_192819 by James Elphick, on Flickr

[Brad Y]

What’s important to remember is SD is what is being looked at. ES will always be larger than SD. But ES tells you what just happened in a string. SD can give you an inclination as to what to expect going forward. I had my 284’s running in the teens for ED but SD was below 10. And that was non sorted brass.

To be honest I’m not in the realm of practically testing. It’s expensive and uses time I don’t necessarily have. But will not argue how sound it is doing the tests for yourself. You will only get out what you put in. Dave and Co. have a nice shiny bit of metal on the shelf to validate their efforts and they still have plenty more in them it seems.

[williada]

James the short answer is yes, yes, yes. Think of it this way, a pressure vessel depends on how it is corked an slow burning powders are not all consumed in the firing chamber either. By varying the seating depth you are altering the pressure particularly peak pressure. Done the experiments with Pressure Trace.

Now to respond to Rob's point. It is not off topic because while the SD's can be higher, they may fall in an individual barrel's zone of harmonic compatibility. There are two aspects to this at the micro and macro level. I examined barrel lift at twenty-five yards as I posted with image a few years ago. In separate testing and I remember Brad and Tony querying short range testing at the time, saying they will go all through the one hole. That tells you something I note some worthy shots still tune at 25 yards. But I examine the micro tunes at 140 yards for reasons I have stated before. With experience you don't need testing at 140 yards or longer will tell you what the barrel is doing.

If a forward of the muzzle tuner is used it can effect the mix of frequencies that flow up and down the barrel about 4 times before the bullet exits. That means it impacts frequencies that alter the bore size at the breach as well as the muzzle. Altering the bore size will effect pressure at the breach but the crown shape will also alter the direction the bullet will start due gas leakage. Getting the timing right is critical. On the macro scale, barrel lift may be timed to effect a compensation tune. Even without a tuner, the shooting platform and fulcrum point together with an adjustment of seating depth can influence both macro and micro tunes. That is while the barrel is lifting minor oscillations are also occurring. An OCW tune requires tight SD/ES for long range shooting. A pure harmonic tune requires strict velocity control to remain on a node. A compensation tune that is mild or enhanced for a specific range requires a specific boundary for ES. So you have to know what your barrel is doing before you can optimize its tune.

[Brad Y]

David that last paragraph has explained more of our conversations than I can remember!

[PeteFox]

OK, since raising the issue and taking on board the helpful criticisms, I still think I am on the right track with the upside down case to eliminate the meniscus.

Back when I was breaking test tubes and collecting environmental samples the BIG thing to avoid in any of this was bias. Bias makes an experiment/survey not worth doing. The sampling must be random and the treatment identical and repeatable, otherwise bias creeps in. At least 2 issues arise:
1.
I still feel that judging the meniscus is too subjective, i.e. in the eye of the beholder, and its measurement or visual estimate is not repeatable if different operators are used. I looked at what I did and my method of inserting a projectile into the neck to seal it is also subjective, subject to my bias and not repeatable by others.
2.
Even though I considered carbon build up inside the case as a factor affecting volume, I erroneously believed that it would be the same (or similar enough) across all cases because they had been fired 3 times each using the same load etc. Wrong again.

So I think I have solved the first issue. I found a silicon stopper that will seal the case mouth without protruding into the neck and allow the case to come to a stop on the bottom and stand vertically on the scale.

seal.jpg

The inside bottom is flat and the seal is around the body of the case. It will be fitted onto the case under water so the extra water captured around the outside of the neck will be the same for each case. I have miked all the necks in three places and they are within +/- 1/4 thou of 0.015". The stopper won't leak so more complete drying of the case will be possible without being pushed for time.

This morning I tried to mechanically remove the carbon from inside the case using a test tube brush on a drill. It was a failure and anyone who has de-coke a cylinder head will understand why. A bronze brush might work but none have bristles on the end to clean the base. I took some interior photos of the case to verify the cleanliness or otherwise.
Case base

caseinsidebase.jpg

Body

caseinsidewall.jpg

Under shoulder

caseinsideneck.jpg

To remedy this I have bought an ultrasonic cleaner online and await its arrival.

I intend to repeat the investigation using the same cases, which should now answer two questions:
Can case volume be inferred by its weight ? and
Does carbon removal/presence significantly affect case volume?
If the answer is yes for the second question then basing loads volumes derived from clean cases is illogical if you use the same load in a dirty case, because the volume will not be consistent.
If anyone can see errors in my logic please let me know.
Pete

[Gyro]

Looks interesting Pete good luck. The volume taken up in the case by the carbon/crud buildup could be interesting too !?

[Wal86]

Anyone actually tested the same ultrasonic cleaned case/ and tested velocities over 10-15 shots..

Same loaded case/therefore exact same volume....................the end result velocities will be different.

So much of this stuff doesn't matter..

Cheers
Alan

[AlanF]

...Even though I considered carbon build up inside the case as a factor affecting volume, I erroneously believed that it would be the same (or similar enough) across all cases because they had been fired 3 times each using the same load etc. Wrong again...

What made you think you were wrong about this? BTW your total approach seems sound to me.

[PeteFox]

...Even though I considered carbon build up inside the case as a factor affecting volume, I erroneously believed that it would be the same (or similar enough) across all cases because they had been fired 3 times each using the same load etc. Wrong again...

What made you think you were wrong about this? BTW your total approach seems sound to me.

Alan,
Wrong because it is a variable I can control. The only uncontrolled variables here should be the case weight and volume.
Also it was just an assumption, I had no evidence to back it up. I’m assessing case weight, not case weight with added carbon as an allegory for volume. Depending on the results of the second test, I may have evidence to support not removing carbon.
It was also biased, in that it was easier to ignore because there was some effort and expense to remove it, and I’m naturally lazy so that would influence my reasoning.
Proper testing should be rigorous and I really want to answer the questions properly.
Pete

[AlanF]

...Alan,
Wrong because it is a variable I can control. The only uncontrolled variables here should be the case weight and volume.
Also it was just an assumption, I had no evidence to back it up. I’m assessing case weight, not case weight with added carbon as an allegory for volume. Depending on the results of the second test, I may have evidence to support not removing carbon.
It was also biased, in that it was easier to ignore because there was some effort and expense to remove it, and I’m naturally lazy so that would influence my reasoning.
Proper testing should be rigorous and I really want to answer the questions properly.
Pete

Okay, not proven wrong, but not worth the risk of degrading the results - fair enough.

On the matter of cleaning the inside of cases with a bronze brush, I'm sure it could be done with the right design, possibly using a hemispherical shaped brush head with a sliding shroud for inserting through the case neck. If someone could manufacture it, it would be much faster and easier than current methods.

[UL1700]

On the matter of cleaning the inside of cases with a bronze brush, I'm sure it could be done with the right design, possibly using a hemispherical shaped brush head with a sliding shroud for inserting through the case neck. If someone could manufacture it, it would be much faster and easier than current methods.

It would struggle to be faster and easier then ultrasonics, 10 mins in the tank, rinse off with metho and flash off with a heat gun and you can be reloading 100 spotless cases in half an hour!

[AlanF]

On the matter of cleaning the inside of cases with a bronze brush, I'm sure it could be done with the right design, possibly using a hemispherical shaped brush head with a sliding shroud for inserting through the case neck. If someone could manufacture it, it would be much faster and easier than current methods.

It would struggle to be faster and easier then ultrasonics, 10 mins in the tank, rinse off with metho and flash off with a heat gun and you can be reloading 100 spotless cases in half an hour!

Really? I didn't realise the drying was that quick. An unfortunate incident I had with a coffee proved that it is essential for them to be perfectly dry inside.

[ajvanwyk]

On the matter of cleaning the inside of cases with a bronze brush, I'm sure it could be done with the right design, possibly using a hemispherical shaped brush head with a sliding shroud for inserting through the case neck. If someone could manufacture it, it would be much faster and easier than current methods.

It would struggle to be faster and easier then ultrasonics, 10 mins in the tank, rinse off with metho and flash off with a heat gun and you can be reloading 100 spotless cases in half an hour!

Really? I didn't realise the drying was that quick. An unfortunate incident I had with a coffee proved that it is essential for them to be perfectly dry inside.

Alan,