reconsidering measuring case weight
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I didnt know so I googled it for all. From Wikipedia, the free encyclopediaamamnn said:
(Redirected from How many angels can dance on the head of a pin)
The question, "How many angels can dance on the head of a pin?" has been used many times as a dismissal of medieval angelology in particular, and of scholasticism in general. The phrase has been used also to criticize figures such as Duns Scotus and Thomas Aquinas.[1] Another variety of the question is: "How many angels can sit on the head of a pin?" In modern usage, this question also serves as a metaphor for wasting time debating topics of no practical value, or questions whose answers hold no intellectual consequence.
CatShooter
jlow said:
I used to think it made no difference.
I have a very (VERY) accurate 308 match rifle, and for some time, back in the late 90's, shot Federal nickeled Gold Match cases.
I had 200, and they weighed ~175grs. +/- maybe a grain.
I needed more cases so I bought 200 more new of the same, shot them, and threw them into the mix.
But the groups went into the toilet and it drove me crazy. Then I went back to the "Prime directive"... "When things suddenly go wrong, look at the last thing you changed".
Since I couldn't tell which cases were which, I decided to weigh them (the first time I weighed cases).
I came up with ~205 that were 175 +/- 1 gr - the rest were all over the place, from 155 to 170, with no particular focus. When I picked 20 from the 175 group, the rifle shot as well.
That was a wake-up call for me. I called Federal, and they wanted all the light cases back right way... I guess if I made them, I'd want them out of circulation too.
I didn't send them back - I just never bought or shot another Federal case after that.
How much does a RED HERRING weigh?
Every time the issue of case volume comes up, and the discussion goes to weighing cases, vs filling with water...
... someone will cloud the conversation with something along the lines of "? Case rim and extractor groove can and do vary, so will weight.", and that pretty much kills any further discussion.
Well... I have this 6mmBR bench rifle that has a 0.262 neck,, and I cut a bunch of Lapua cases for a pending PD trip to 0.261"... a little "tight", but I could reload in the motel if I had to, without sizing.
The trip never panned out and the rifle was a spoiled Prom Queen to shoot - it was fussy, and needed to be cleaned about every three shots, and generally was a pain in the butt... so it collected a lot of dust in the back of the safe.
Some years back, I watched Jack Neary's video series, and he said he had the same problem with his 6mm bench rifle (a PPC), he was running a 0.001 clearance neck and the rifle drove him crazy, so he cut it larger (2.5 thou total), and all was good.
So I cut 40 cases down to 0.2596" (0.0083" wall), and the rifle finely came home - no matter what I loaded, it shot well and became a sweetheart.
So I was now looking at 760 cases to be turned down to 0.0083", and the bucket sat there for years and years, cuz turning necks is my second least favorite thing to do.
Yesterday at 6 PM, I decided to turn them all down and be done with it
I finished at 5 AM this morning.Now what is this all about.
Half way through it I was thinking about this thread and all the times guys killed the weighed case discussion with "? Case rim and extractor groove can and do vary, so will weight." type comments...
... so I took a case and measured the neck (0.0091") and weighed it. Then I turned it down to 0.0083" and weighed it again - 0.6 grains lost.
So we have a cylinder that is 0.3" long, and ~.260" in diameter, and (including both sides) 0.0016" thick, weighs 0.6gr.
The width of an extractor groove is ~0.03... so that is 1/10th of our 0.3"long, 0.6gr cylinder.
So to clear all the "Stuff away in a more reasonable presentation - for every 0.0016th of an inch difference in extractor groove diameter, you lose or gain 0.03 grains in case weight!
Which is to say - discussing extractor groove variations in a case weighing thread is shear idiocracy and the reddest of herrings.
Read jlow's efforts here, they spell it out very well:
http://forum.accurateshooter.com/index.php?topic=3858399.45
P.S.... never turn case necks for 11 hours straight, it makes you crazy!
CatShooter
mikecr said:
If you know the volume of the brass, you don't need the volume of water, which will vary due to many factors that you cannot control.
What you indicated above is the reason why there is so much disagreement about the correlation between case weight and volume.mikecr said:
The root of the problem with negative data like the ones generated by Donovan is that unless the technique is validated, it is not proof. What I mean is unless you show proof that your technique can detect the small changes equal to the change in weight, not being able to show a correlation between weight and volume is not proof. This is a basic foundation people follow in research and applies in this situation.
If you change the Initial confinement from a case(regardless of it's weight), you can see a change to MV with it from a given load. Do you believe this?
If you use QL, and have it well calibrated to your barrel/powder lot, go ahead & fiddle with H20 capacity a bit and consider the results to both MV & barrel time.
I'll concede that H20 capacity variance may not be a factor with a gun running a pressure node. That is, the bullet is jammed, and running fast powder at extreme pressures, as with point blank underbores.
But with LR cartridges that are not jammed and running viable pressures, capacity variance would manifest similar to neck tension variance.
I don't have a scientific study to prove it, would like to see one.
It's just my notion I guess. I think initial confinement matters a lot.
If you use QL, and have it well calibrated to your barrel/powder lot, go ahead & fiddle with H20 capacity a bit and consider the results to both MV & barrel time.
I'll concede that H20 capacity variance may not be a factor with a gun running a pressure node. That is, the bullet is jammed, and running fast powder at extreme pressures, as with point blank underbores.
But with LR cartridges that are not jammed and running viable pressures, capacity variance would manifest similar to neck tension variance.
I don't have a scientific study to prove it, would like to see one.
It's just my notion I guess. I think initial confinement matters a lot.
CatShooter
mikecr said:
No... The case walls open very fast and seal the chamber - so the case reaches it's "working volume" almost instantly.
This is all spculation and has no bearing on real stuff.
On occasions, I have had to add a new, unfired case into a group of fired cases, and to my surprise (the first few times) there was no measurable change in velocity or POI... they fell right into the group.
It is my experience that "initial confinement" is another made up "pseudo theory" that holds no H2O, and matters not one bit.
It is easy to theorize on the couch - but try this stuff and see what happens. Often, it will surprise you.
Seems like there are a number of slightly related items here being discussed at the same time which can be confusing.
I think at least to me, there is the initial question of case weight vs. case volume, this stands by itself.
A second question is if case volume is actually different (regardless of whether it is new brass, size or unsized fired brass but comparing within the same group), does this affect chamber pressure?
A third what mikecr just brought in is the initial confinement which I gather is defined as a case that has been sized smaller or has not been blown out to chamber dimensions. The question appears to compare this initial confinement case to one that has been blown out to full chamber dimension. This is an interesting question but not really related to the above as the difference is in the initial volume but how does it does relates to the first two questions?
I think at least to me, there is the initial question of case weight vs. case volume, this stands by itself.
A second question is if case volume is actually different (regardless of whether it is new brass, size or unsized fired brass but comparing within the same group), does this affect chamber pressure?
A third what mikecr just brought in is the initial confinement which I gather is defined as a case that has been sized smaller or has not been blown out to chamber dimensions. The question appears to compare this initial confinement case to one that has been blown out to full chamber dimension. This is an interesting question but not really related to the above as the difference is in the initial volume but how does it does relates to the first two questions?
CatShooter
dedogs said:
I would think that, whatever variables there are, fall inside the grouping window ("node" is a terrible misnomer),... then it should not matter.
I have several rifles (big - 14 to 15 pound class) that do not show preferences - you increase the powder, and the same sized group appears a little higher on the target.
Some rifles are so fussy that if clouds appear, the group goes to hell.
This is specifically the reason why I weight sort your brass. I recently dealt with a 3 grain Lapua 308 brass variation by buying 500 cases, weight sort them and dividing them into three batches which I will use separately. That way, there will only be a 1 grain spread within each group.dedogs said:
Anytime you use a granular material with an irregular surface texture, you are asking for less than perfect packing which in turn affects the % of the mixture which is made up of the particulate vs. air. As long as you cannot get exactly the same packing efficiency as a liquid, you are not going to get as accurate and reproducible volume determination. This is the reason why people use liquids instead of solid particulates for volume determination. Even water is not the best because of the tendencies to leave bubbles inside the case and that is the reason why people use rubbing alcohol; not to mention that it has a lower surface tension and so less of a tendency to form a meniscus which also affects your ability to measure accurately.
In the end, you can use whatever you want, but if you want to have meaningful data to help you move forward, you must first proof to yourself that the error in your measurements is significantly less than the degree of change you are expecting in your sample. If you can do this, you are golden, if you cannot, then none of your data means anything.
In the end, you can use whatever you want, but if you want to have meaningful data to help you move forward, you must first proof to yourself that the error in your measurements is significantly less than the degree of change you are expecting in your sample. If you can do this, you are golden, if you cannot, then none of your data means anything.
This might be slightly off-topic, but what exactly is the "standard procedure" for measuring the water capacity of a case?
Do you use resized, trimmed-to-length cases, and if so, how do you plug the flash hole?
Do you use a wetting agent such as detergent or alcohol?
If not, how do you ensure the consistency to the size of the meniscus or whatever it's called (the "bulge" of water that protrudes from the neck due to the surface tension of the water) and how do you make sure there are no air bubbles hidden inside the case?
What about droplets of water that adhere to the outside of the case? Do they make a significant difference in weight, and if so, how do you get rid of them?
The whole process as I envision it just seems really messy and chock-full of potential errors...but I've never tried it, so I don't know.
Do you use resized, trimmed-to-length cases, and if so, how do you plug the flash hole?
Do you use a wetting agent such as detergent or alcohol?
If not, how do you ensure the consistency to the size of the meniscus or whatever it's called (the "bulge" of water that protrudes from the neck due to the surface tension of the water) and how do you make sure there are no air bubbles hidden inside the case?
What about droplets of water that adhere to the outside of the case? Do they make a significant difference in weight, and if so, how do you get rid of them?
The whole process as I envision it just seems really messy and chock-full of potential errors...but I've never tried it, so I don't know.
Synocrowave, I tried used and new primers with very little consistent repeatability. 21st Century makes a primer plug that works great, and gives repeatable results. After filling case, I use a light weight machinist's rule and push down as I lay the ruler across the case mouth removing meniscus, forcing water over the side of the case. All the while, I am holding the case wrapped in a small cotton cloth. Then dry the case and plug as needed with cloth. Even the slightest moisture on the outside of the case will effect weight. Results are repeatable with distilled water (tap would probably work), I use at approx 70 degree F. Temp variation will cause water density variations, but for our use a few degrees won't matter I believe. Also, let tap water sit for a day or 2 in a loosely covered cup, to let air work it's way out. The above method will give repeatability to within .002 gram (.03 grain) or less, most of the time. A case that seems too light, typically contains an air pocket, and is reweighed. When this is done, the primer pocket must be dried or your weight will be off a 2nd time. All cases are fire formed to chamber and not resized. I personally use SSM to clean inside and primer pockets before weighting. Also case length needs to be as close as is possible to the same dimension throughout. I am certain that I will be flamed by some, as there are as many ways to do this as there are people doing it. This works for me. A lot of work is involved, and as exciting as watching grass grow.
Jim,
just out of curiosity, since you have gone through the tedious process of actually measuring volume of fire formed brass, could you give us the differences of case weight between cases with equal volume? Thanks.
just out of curiosity, since you have gone through the tedious process of actually measuring volume of fire formed brass, could you give us the differences of case weight between cases with equal volume? Thanks.
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