Measuring Case Volume vs time-intensive case preps

[seymour fish]

measuring case volume, despite the naysayers, is simple, quick, and easy. It is repeatable. Why quibble over powder charge to the kernel when your combustion chambers capacity varies ? This seems a bedrock issue to me. Many brass tweaks are "flavor of the month", falling in and out of favor, and consuming time better spent elsewhere, i.e. Producing a matched set of combustion chambers. Some lots of high quality brass will be found to have near-identical case vol after fire forming, despite some fluctuation in weight. Fortuitous, producing "accidental" good loads. Some weight-matched cases will have fire-formed case capacity variance. Retorically, would an engine-builder be considered competent if he failed to cc and match your combustion chambers ? Is internal combustion internal combustion ? Is this one of the underlying reasons why throwing away a case which refuses to print with the rest has been a time-tested common sense approach ? Onward, to the basics. Let the flames begin. Seymour

 

[T-shooter]

I've tried the water method. Have a better idea?

 

[seymour fish]

I've tried the water method. Have a better idea?

T, the water method is all you need. Tap the case mouth a couple times on a board to knock out any loose carbon. Fill case to point of a surface tension lenticular bulge. If some runs over, no problem, mop it off the case with a paper towel. FX scale. Careful not to spill any, get any on scale. Learning curve short and shallow. Give it another chance

 

[mikecr]

I've tried the water method. Have a better idea?

Assuming you had some kind of issue with it, I'd suggest learning, and solving whatever it was.

 

[T-shooter]

Assuming you had some kind of issue with it, I'd suggest learning, and solving whatever it was.

No issue except it is time consuming to do in an quanity. I used a 50cc syringe and fill from the bottom to prevent air pockets. Best to resize first leaving the spent primers in the cases, then remove later.

 

[Ron Blain]

I was curious about this so began my own little science experiment. I randomly selected 10 Each of Remington, Winchester, WCC 10, LC 13 and Federal Match empty cases. I ran all 50 cases through a sizing die followed by trimming. All cases were also cleaned and had their primers removed. I weighed all 50 cases making note of each case weight. To close the primer flash holes I used modeling clay, the same clay used for glass bedding type operations. Each little ball of clay weighed 1.8 grains. I used a syringe to fill each case with standard tap water which is good enough and my pot of water had a few drops of Dawn Dish Detergent so the water would easily level at the case mouths. Below are the results:

Getting down to actual case volume the smallest standard deviation was the WCC 10 brass. I have yet to get around to loading the cases but will likely load 150 grain Sierra Match King bullets over about 44 grains of AA 2495 and run them through one of my bolt guns. I'll also run them over the chronograph just to get a general idea of velocities. Primers will likely be CCI, maybe some BR 2. No, I don't do this for all brass I load, this just being a curiosity thing.

Ron

 

[Bart B.]

Case water fillers need to have each case full into a full length sizing die so it's outside dimensions and shape is identical across all cases. Otherwise their normal out of round condition will skew their capacity.

Elipses with the same circumference as a circle have less area.

Are all your cases perfectly round?

 

[T-shooter]

I was curious about this so began my own little science experiment. I randomly selected 10 Each of Remington, Winchester, WCC 10, LC 13 and Federal Match empty cases. I ran all 50 cases through a sizing die followed by trimming. All cases were also cleaned and had their primers removed. I weighed all 50 cases making note of each case weight. To close the primer flash holes I used modeling clay, the same clay used for glass bedding type operations. Each little ball of clay weighed 1.8 grains. I used a syringe to fill each case with standard tap water which is good enough and my pot of water had a few drops of Dawn Dish Detergent so the water would easily level at the case mouths. Below are the results:

Getting down to actual case volume the smallest standard deviation was the WCC 10 brass. I have yet to get around to loading the cases but will likely load 150 grain Sierra Match King bullets over about 44 grains of AA 2495 and run them through one of my bolt guns. I'll also run them over the chronograph just to get a general idea of velocities. Primers will likely be CCI, maybe some BR 2. No, I don't do this for all brass I load, this just being a curiosity thing.

Ron

Nice chart. I checked a few before but just one each for a ballpark idea between brands. I went through 50 Hornady cases and picked the lightest and heaviest. In the past I had overpressure issues with CBC brass. No wonder, it has almost the smallest capacity. These could be more accurate. I didn't have my FX scale then.

 

[Ron Blain]

Case water fillers need to have each case full into a full length sizing die so it's outside dimensions and shape is identical across all cases. Otherwise their normal out of round condition will skew their capacity.

Elipses with the same circumference as a circle have less area.

Are all your cases perfectly round?

Bart, they were as round as a baby's butt! Really they were as good as they were going to get if I was to load them. When all was said and done I really have to wonder how much the case capacity would really matter in the big picture? Take a look at those case volumes expressed in cc. Oh, I forgot to mention following cleaning each case had a brush mounted on a case prep center run on the inside. I'll see what I get but really my guess is things like the actual brass neck tension will likely have a greater effect than those case capacity differences. There really isn't much there, not enough to really matter as I see it. They were sized and trimmed and any spring changes in the brass I see as not really being a concern because any change would likely not come in light of the final numbers. So while I agree as to an ellipse I doubt it matters enough in this case.

Ron

 

[Ron Blain]

T-Shooter, real nice chart you came up with. The numbers are close which runs with my findings.

Ron

 

[Bart B.]

Bart, they were as round as a baby's butt! Really they were as good as they were going to get if I was to load them. When all was said and done I really have to wonder how much the case capacity would really matter in the big picture?

Never seen anyone's butt perfectly round. 'Course I've never checked out enough to be statistically confident.

I weigh cases to a 1% spread about average weight. They shoot bullets as accurate as anyone's when tested to 98% confidence levels. No case prep, either. Just use decent cases to start with.

 

[Ned Ludd]

I don't find measuring case volume with water to be difficult, but it is time-consuming and I don't do it for all of the hundreds of cases I use in competition. On numerous occasions I have measured case volume with water for cases of known weight. There is always a general inverse trend for case weight versus case volume. However, there are always a few outliers where case weight does not match up well with case volume (i.e. they're well off the trend line).

Regardless, I still sort cases by weight and I figure even if case weight doesn't always correspond perfectly to case volume, the weight sorted case will still be more uniform in terms of volume than if I do nothing at all. I can weight sort a few hundred cases in well under an hour. Sorting the same number of cases using water volume would take considerably longer.

In response to Seymour's original question, I think the best answer lies in the concept of limiting source of error. Which condition would have the greater effect on velocity/pressure: 1) varying charge weight by a tenth of a grain in cases of the exact same internal volume, OR 2) having the exact same charge weight in cases where the internal volume may differ by a tenth up to a few tenths of a grain?

In this example, I think Quickload might give some insight to which factor (case volume versus charge weight) might be the larger source of potential error, at least in as much as you have faith in QL predictions/outputs. I used one of my .223/90 VLD loads as a starting point and 1) adjusted charge weight up by 0.1 gr, or 2) adjusted case volume up by 0.1 gr. Here are the QL predictions/outputs:

As you can see from the Table, increasing charge weight by 0.1 gr had a 3-fold greater effect on predicted velocity/pressure than did changing case volume by 0.1 gr. In this example, I know from testing that the predicted increase in velocity going from 24.2 gr to 24.3 gr is spot on the increase I actually measure with the chronograph. I have not ever loaded cases that differed in volume by ~0.1 gr and tested those to determine how good QL's prediction there actually. However, these predictions at least suggest that as measured in grains, charge weight will have the greater effect on velocity/pressure by a factor of slightly more than 3X.

During the reloading process, there are many things we do as reloaders that probably go far beyond what we can realistically assess with confidence on the target. Identifying and understanding the the largest potential sources of error can be a useful exercise in deciding what steps you consider "essential" and those you may not always choose to implement, except perhaps for really critical matches. It is important to note that the one element of this process that cannot be defined other than in individual terms is the peace of mind and/or confidence you get by going the extra mile. I'm positive that on a theoretical basis, some of the reloading steps I carry out for important matches have an effect so small as to be statistically insignificant. However, I place a high value on having confidence when I get behind the rifle for a match that there is little more I could have done to improve my ammunition. For that reason alone, it is personally worth it to put forth the extra effort. Everyone must decide for themselves what steps they consider "essential" and what steps may not be worth the extra time and effort.

 

[seymour fish]

I don't find measuring case volume with water to be difficult, but it is time-consuming and I don't do it for all of the hundreds of cases I use in competition. On numerous occasions I have measured case volume with water for cases of known weight. There is always a general inverse trend for case weight versus case volume. However, there are always a few outliers where case weight does not match up well with case volume (i.e. they're well off the trend line).

Regardless, I still sort cases by weight and I figure even if case weight doesn't always correspond perfectly to case volume, the weight sorted case will still be more uniform in terms of volume than if I do nothing at all. I can weight sort a few hundred cases in well under an hour. Sorting the same number of cases using water volume would take considerably longer.

In response to Seymour's original question, I think the best answer lies in the concept of limiting source of error. Which condition would have the greater effect on velocity/pressure: 1) varying charge weight by a tenth of a grain in cases of the exact same internal volume, OR 2) having the exact same charge weight in cases where the internal volume may differ by a tenth up to a few tenths of a grain?

In this example, I think Quickload might give some insight to which factor (case volume versus charge weight) might be the larger source of potential error, at least in as much as you have faith in QL predictions/outputs. I used one of my .223/90 VLD loads as a starting point and 1) adjusted charge weight up by 0.1 gr, or 2) adjusted case volume up by 0.1 gr. Here are the QL predictions/outputs:

As you can see from the Table, increasing charge weight by 0.1 gr had a 3-fold greater effect on predicted velocity/pressure than did changing case volume by 0.1 gr. In this example, I know from testing that the predicted increase in velocity going from 24.2 gr to 24.3 gr is spot on the increase I actually measure with the chronograph. I have not ever loaded cases that differed in volume by ~0.1 gr and tested those to determine how good QL's prediction there actually. However, these predictions at least suggest that as measured in grains, charge weight will have the greater effect on velocity/pressure by a factor of slightly more than 3X.

During the reloading process, there are many things we do as reloaders that probably go far beyond what we can realistically assess with confidence on the target. Identifying and understanding the the largest potential sources of error can be a useful exercise in deciding what steps you consider "essential" and those you may not always choose to implement, except perhaps for really critical matches. It is important to note that the one element of this process that cannot be defined other than in individual terms is the peace of mind and/or confidence you get by going the extra mile. I'm positive that on a theoretical basis, some of the reloading steps I carry out for important matches have an effect so small as to be statistically insignificant. However, I place a high value on having confidence when I get behind the rifle for a match that there is little more I could have done to improve my ammunition. For that reason alone, it is personally worth it to put forth the extra effort. Everyone must decide for themselves what steps they consider "essential" and what steps may not be worth the extra time and effort.

Taylor, Thank you for this excellent analysis. Many F-TR shooters are weighing powder to the limit of an FX120 scale i.e. 0.02 grains. Using your 3:1 ratio, which matches ones intuition about these matters, to maintain the same precision re: powder capacity, if not OCD, would require 0.06 gr. Your QL outputs are instructive and valid. Ron' s post above, also very nicely done, highlights the probability that there is considerably more than our 0.06 capacity variance out there, some brands being more uniform than others. Just how exactly can a set of brass be matched, and at what time and material cost. being ignored, consider the errant under capacity case, on a hot day, going just off the node. Perhaps there is a brand of case that we gravitate toward which maintains near-identical case capacities and thus shoots well "by accident". any chance it starts with L ?

 

[Ned Ludd]

Taylor, Thank you for this excellent analysis. Many F-TR shooters are weighing powder to the limit of an FX120 scale i.e. 0.02 grains. Using your 3:1 ratio, which matches ones intuition about these matters, to maintain the same precision re: powder capacity, if not OCD, would require 0.06 gr. Your QL outputs are instructive and valid. Ron' s post above, also very nicely done, highlights the probability that there is considerably more than our 0.06 capacity variance out there, some brands being more uniform than others. Just how exactly can a set of brass be matched, and at what time and material cost. being ignored, consider the errant under capacity case, on a hot day, going just off the node. Perhaps there is a brand of case that we gravitate toward which maintains near-identical case capacities and thus shoots well "by accident". any chance it starts with L ?

FWIW - I weigh powder on a high end Mettler analytical balance to +/- less than half a kernel. That is far finer an increment than is necessary, most definitely gross overkill. However, the manner in which I dispense and weigh powder is such that weighing to +/- 10 kernels would still take me about the same amount of time, so I've always figured why not take it out to a level where I'll never, ever, ever have to worry when I'm on the firing line at a match that I could have weighed my charges to a finer degree of precision. If it took me ten or twenty times longer to measure powder to that level, I wouldn't be doing it.

I think in general most everyone has their particular reloading practices, some of which may fall into the uber-OCD overkill category. That's ok, being extra careful only slows things down. Not being careful enough will often cost points.

 

[Bart B.]

I've shot 308 Win ammo with a 3/10ths grain spread in charge weights shooting about half MOA extreme spread for 20 shots at 600 yards.

 

[wapiti25]

I also watch for cases that do not shoot in the same group, they get culled.

 

[Ray B]

While I sort cases for similar internal capacities I also use several other steps to insure that the loaded ammunition is as identical as possible. It may be OCD, but for the amount of rounds involved, it's well spent time. Now if I were shooting the amount that a friend of mine does in trap, it would be prohibitive.

 

[swd]

Never seen anyone's butt perfectly round. 'Course I've never checked out enough to be statistically confident.

Oh there was a girl in highschool named Nancy. Can't remember her last name, been too long. It was magnificent! And I wasn't alone in that opinion.

 

[seymour fish]

I've shot 308 Win ammo with a 3/10ths grain spread in charge weights shooting about half MOA extreme spread for 20 shots at 600 yards.

Bart, my m-14's do the same, loaded on a Dillon using their powder dump. Don't want to know what the powder spread is. Might ruin the "magic". All that aside, the thread is an attempt to take a hard look one element in the accuracy equation. Many thanks to Taylor, T, Ron, Ray, Wapiti, and of course "Nancy", for the education. Seymour

 

[Bart B.]

Bart, my m-14's do the same

That's the most accurate M14 I've heard of.