Sorting primer velocity with the Garmin Xero

[Rocketvapor]

Went to the 600yd range in Bogalusa to test some Heavy and Light CCI 450 primers.
22Nosler AR-15, Berger 85.5, 31.7gr SB 6.5
Grouped some 3.62/3.63 light ones, and some 3.73/3.75 heavy ones, 5 each, shot round robin light first.

The light/ heavy individual velocities, Garmin Xero:
Light 2989.3
*Heavy 3039.3
*Light 2975.2
Heavy 3007.7
Light 2996.5
Heavy 3018.5
Light 2993.2
Heavy 3011.4
Light 2997.4
Heavy 3015.7

Went back 2 weeks later and did a larger sample with individual primer weights recorded and post fired primer weight.
15 light, 15 heavy. Shot round robin heavy first. 22N AR-15, Berger 85.5, 31.8gr SB 6.5
Weighing performed with an A&D EJ-54D2, on low range (0.005grain resolution)

Shot Order, Primer Weight, Fired Primer Weight, Weight Loss, Garmin Xero Muzzle Velocity.
1 -- 3.765, 3.400, 0.365, 3036.8
30 - 3.625, 3.375, 0.250, 2989.2
2 -- 3.760, 3.390, 0.370, 3042.7
29 - 3.625, 3.360, 0.265, 2989.0
3 -- 3.765, 3.385, 0.380, 3054.4
28 - 3.620, 3.360, 0.260, 2987.4
4 -- 3.775, 3.405, 0.370, 3058.4
27 - 3.615, 3.370, 0.245, 2993.1
5 -- 3.755, 3.395, 0.360, 3050.2
26 - 3.610, 3.360, 0.250, 2977.4
6 -- 3.755, 3.395, 0.360, 3046.2
25 - 3.630, 3.380, 0.250, 2996.3
7 -- 3.750, 3.395, 0.355, 3037.8
24 - 3.630, 3.370, 0.260, 2982.8
8 -- 3.750, 3.385, 0.365, 3047.0
23 - 3.630, 3.370, 0.260, 2992.5
9 -- 3.750, 3.390, 0.360, 3055.4
22 - 3.635, 3.370, 0.265, 2987.9
10 -- 3.750, 3.390, 0.360, 3029.2
21 - 3.635, 3.365, 0.270, 3021.1
11 -- 3.740, 3.380, 0.360, 3055.1
20 - 3.635, 3.360, 0.275, 3010.1
12 -- 3.730, 3.385, 0.345, 3053.5
19 - 3.630, 3.360, 0.270, 3010.3
13 -- 3.730, 3.380, 0.350, 3063.0
18 - 3.635, 3.360, 0.275, 3013.2
14 -- 3.730, 3.380, 0.350, 3032.3
17 - 3.635, 3.370, 0.265, 3003.1
15 -- 3.730, 3.385, 0.345, 3044.6
16 - 3.640, 3.375, 0.265 2999.9

Range of primers: 0.165 grains
Range as fired: 0.045 grains
Range of weight loss: 0.135 grains
Extreme Spread of all 30 shots, Garmin Xero muzzle velocities 85.6 fps.
Extreme Spread of 15 HEAVY 33.8fps SD 9.6
Extreme Spread of 15 LIGHT 43.7fps, SD 12
Picture of Shot Marker target of 10 shots 3/7/24 and first 10 shots on 3/21/24.
Shot marker was acting up (I think) on 3/24 ??? Note avg velocity and POI started shifting right.

Also posted on a couple other forums.

 

[375fan]

Explain the light/heavy primer thing. Are you weighing and sorting each and every primer?
If so, what are you using for a scale.

 

[Rocketvapor]

YES, looking for outliers in primer weight and the effect on velocity

 

[OREGUN]

Interesting. I’m never sure it’s possible to slice the data this thin. The margin of error in your scale, the chrono, the shot marker, hell even the humidity in the powder, all combined to muddy the water more than 3 fps over 15 shots. It would be interesting to see the results of a sample twice as big….at least 30 per weight.…to more adequately validate statistics like SD. How are you decapping in a way that leaves you confident that you haven’t changed the weight of the primer in the process? At the end of the day, if this leaves you more confident that your ammo is better and you have time and excess primers to allow for sorting, it won’t hurt.

 

[Rio Precision Gunworks]

Interesting. I’m never sure it’s possible to slice the data this thin. The margin of error in your scale, the chrono, the shot marker, hell even the humidity in the powder, all combined to muddy the water more than 3 fps over 15 shots. It would be interesting to see the results of a sample twice as big….at least 30 per weight.…to more adequately validate statistics like SD. How are you decapping in a way that leaves you confident that you haven’t changed the weight of the primer in the process? At the end of the day, if this leaves you more confident that your ammo is better and you have time and excess primers to allow for sorting, it won’t hurt.

Agreed. There's too many other variables you'd have to eliminate to make the primer weight observable.

Though I do think looking it over, it's fair to correlate heavier primers with higher velocity. Which would make sense. The rest of the data I'd say isn't enough yet or likely not able to be controlled enough to do much else with...even long term. Mostly anyway.

 

[Rio Precision Gunworks]

Also, FWIW, for your light charges listed in white on the 15 rounds per, your low velocity is 2977 and high is 3021 for an ES of 44 and not 30.4.

 

[Rocketvapor]

Thanks, corrected. That's a lot of numbers
This is posted for anyone that might think primer weight IS important.
The excess outliers still gave me trigger time so no waste.
Total rounds for both tests was 40 rounds. I think that's enough to form an 'opinion'.

My reloading process (when I pay close attention) is to weight sort (not volume) brass.
These were all within 0.2 grains. I still have them and will use them for another practice session with a narrower primer weight range. 2, or more firings and the pockets seemed fine when I deprimed them.
The bullets were sorted first to OAL (+/- 0.002") then weight to +/- 0.05 grains.
Primer weights, giving a count for zero, and a count for weight are accurate to an estimated 0.010grain.
(try that with your 120i )
The scale is calibrated on the low range @ 10 grams and checked with ASTM 1 gram, 5 gram and a 10gram weights from 2 to 10 grams.
It does have a little better resolution in gram mode (0.0002 g) but grain mode is good enough. Still better than that FX120i but a LOT slower.

I use it for things other than reloading and it performs well.
Powder, SB 6.5, a fine ball powder, was weighed to an indicated 0.010 GRAIN (that's +/- 2 counts).
Charges were adjusted to the target value by adding/subtracting one or two little granules (about 0.005grains each ).
Loading area was @ 50 to 52%RH 71 to 72F for hours. All charges should have had the same moisture content.
Charges were done sequentially 1, 2, 3----30, shot 1, 30, 2, 29, 3, 28.
The light and heavy velocities (Garman Xero) were still a range of primer weights. Not one weight for high, or low.
Some of the light ones and heavy ones came real close to overlapping.
I shot what I had available.
For what it's worth, I have found similar primer weight ranges in CCI 41, BR4, WIN41, and Ginex.
AS far as the ShotMarker, I'm not a big believer, but the groups "sort of" bear out Heavy goes higher than Lighter.
The as fired primers, carefully deprimed but not cleaned, had a range of weight that did follow unfired weight.
So cup/anvil was a contributor. About 25% of the weight change was metal/soot leftover, about 75% was lost by firing.

I'm currently an 'Expert' Midrange F-Open shooter (AR in 22Nosler) trying to make Master. Almost an MOA @ 600, but not quite. Get rid of a few 9's and I might make it.
E.S. seems to be more suited for eliminating fliers, while SD for overall group size.
The Heavy and Light groups were pretty good for me.
Thanks for even looking this over.

 

[Maurygold]

There’s no baseline to work from and too many variables to extrapolate something from this. I would rather see what no sorting es looks compared to a non-sorted group. Then we can tell if sorting brought it down any statistically significant amount (the testing from others shows it won’t)

 

[Rio Precision Gunworks]

Thanks, corrected.
This is posted for anyone that might think primer weight IS important.
The excess outliers still gave me trigger time so no waste.

I think you're fairly well showing the heavier the primer, the more compound it likely has, and therefore more velocity.

Testing on this subject in the past has shown that the closer you are to the middle primer weight, the more consistent things get (group size and chronograph). So, you could likely sort primers via weight, then use the outlying weights on both sides as foulers or other such uses. If you want to actually sort primers. Though I'm not away of any extremely high round count tests on the subject.

I'm not sure if he still does it, but F Class John was definitely weight sorting his primers not too long ago and claimed he was able to see a difference.

 

[Rio Precision Gunworks]

And by default, if heavier primers are faster than lighter primers......you can reduce your chrono numbers excluding using the primers on the far ends of weight.

 

[OREGUN]

I suppose if you wanted a higher velocity without adding powder, it looks like you could use only “heavy” primers and get a little bit. There does seem to be something there.

It would be interesting to see es/sd of say 50 each of “heavy”, “light”, and “unsorted” to see which gives better consistency. If pure consistency is what you are after, that should be the next test. And maybe a group with “in the middle” primers by mean weight or within 1 SD of the mean.

 

[ZA206]

No matter what your data shows, I flat out refuse to weigh primers. I can’t do it… I’m just not that anal.

Thanks for the data and the effort, it’s interesting!

 

[Maurygold]

I think you're fairly well showing the heavier the primer, the more compound it likely has, and therefore more velocity.

Testing on this subject in the past has shown that the closer you are to the middle primer weight, the more consistent things get (group size and chronograph). So, you could likely sort primers via weight, then use the outlying weights on both sides as foulers or other such uses. If you want to actually sort primers. Though I'm not away of any extremely high round count tests on the subject.

I'm not sure if he still does it, but F Class John was definitely weight sorting his primers not too long ago and claimed he was able to see a difference.

Then why do the heavier ones remain heavier after firing? Looks like a cup thickness not the charge compound.

 

[Rio Precision Gunworks]

I suppose if you wanted a higher velocity without adding powder, it looks like you could use only “heavy” primers and get a little bit. There does seem to be something there.

It would be interesting to see es/sd of say 50 each of “heavy”, “light”, and “unsorted” to see which gives better consistency. If pure consistency is what you are after, that should be the next test. And maybe a group with “in the middle” primers by mean weight or within 1 SD of the mean.

The interesting part is, if primer weight is correlated to muzzle velocity, you can by default make your chrono numbers more consistent via only using primers from the middle two or middle four weights. As you'd be eliminating higher and lower velocities on each end of the bell curve.

 

[Maurygold]

85 es without sorting is also very high. Seems like something is up there which makes it hard to extrapolate data from this to correlate.

 

[memilanuk]

Then why do the heavier ones remain heavier after firing? Looks like a cup thickness not the charge compound.

Residue consistent with the difference in priming compound?

Others have dismantled and ultrasonically cleaned and measured the metal bits in the past - IIRC they are stupidly consistent, beyond what most of us have the scales see the difference in.

 

[OREGUN]

The interesting part is, if primer weight is correlated to muzzle velocity, you can by default make your chrono numbers more consistent via only using primers from the middle two or middle four weights. As you'd be eliminating higher and lower velocities on each end of the bell curve.

View attachment 8379366

I was just meaning if he wants to find the most consistent set he’s got to keep slicing it down to the smaller pieces. Of course, only shooting the two weights in the middle of that whole group should give the smallest extreme spread of that whole group.

 

[Rocketvapor]

I have routinely shot a narrow range of primer weights (still haven't made Master).
By doing this I collected some heavy/light ones.
All gone now.
Wife will probably make it before me but she is cheating. Shooting a Savage Bolt gun I put together as a Christmas present.
Unsorted has the chance of including some extreme outliers.
Not knowing sort of defeats the purpose of sorting.

I know many good/great shooters don't bother sorting primers, some don't even sort bullets, or shoot better brass and don't sort them either (unless they are closet sorters ).

 

[OREGUN]

Residue consistent with the difference in priming compound?

Others have dismantled and ultrasonically cleaned and measured the metal bits in the past - IIRC they are stupidly consistent, beyond what most of us have the scales see the difference in.

I’m not sure what evidence out there could possibly convince me that anything meaningful can be gained from a post firing, post removal, weight of a primer. All that shows is what parts of that primer you happen to have collected from that case at that particular moment. You guys have never had crumbs fall out of a primer in decapping? Is there any reason to think that the part you pull out to weigh could possibly be consistent from firing to firing and case the case? I guess maybe in a lab setting you could discharge a primer in a closed container and then weigh the mass of whatever remained after you released whatever gas it was you thought wasn’t important to measure but once again, what meaningful information could possibly be gained from that?

 

[Rocketvapor]

How much 'residue' do you think is left in a metal as-fired primer?
I still have them, in order fired.

Sure glad I put up all the data in one post
Why the as-fired weight was heavier for the heavy primers and the as-fired weight was less for the lighter ones?
No idea. Sort of like two groups of cup/anvils.
I think the weight range unfired, and weight loss pretty closely follows velocity.
Maybe some statistical guru could do some mumbo-jumbo to correlate weight loss to velocity

 

[OREGUN]

How much 'residue' do you think is left in a metal as-fired primer?
I still have them, in order fired.
View attachment 8379401

I think the weight range unfired, fired, and weight loss pretty closely follows velocity.
Maybe some statistical guru could do some mumbo-jumbo to correlate weight loss to velocity

Well, here’s a 450 I pulled apart. Aside from the metal bits there’s the rest of that stuff. If we are already talking about weights down to 1/1000 of a grain, which is something like 6 hundredths of a milligram, isn’t nothing.

 

[OREGUN]

And I’m not saying you’re not removing and weighing something. I’m just saying that it means absolutely nothing.

 

[Rocketvapor]

Weigh the crud.
Would a heavier primer leave more crud behind?
How much of the as-fired weight in that one example?
Mine MIGHT do it. Here's 139 counts for a medium kernal of Varget.

Logs of IMR 4350

 

[Rocketvapor]

Not that it matters, other than heavy primers lost more weight than light primers.

SD of weight loss, 15 heavy primers is 0.0094 with
a mean of 0.3597grains, min max of 0.345 to 0.380grains (about a 10.1% range)

SD of weight loss, 15 light primers is 0.0091 with
a mean of 0.2617 grains, min max of 0.245 to 0.275grains (about a 12.2% range).

That's a 37.4% difference in loss between heavy and light primers.
(with an unknown amount of crud left behind)
Did I miss any numbers again?

 

[milprileb]

I would contribute to this but since I am the Variable to my superb rifles at 1000 yd line, my 65 year quest to improve has not crossed the finish line. Hold that thought on SD's and primers till I get there. You Wizards press on, I'll catch up but don't hold your breath.

 

[TheOfficeT-Rex]

@Rocketvapor
What's the expected or usual velocity & SD from this load over 15 shots (without sorting primers)?

 

[Rocketvapor]

31.7gr of SB6.5 about 2990fps,
31.8gr of SB6.5 about 3000fps
SD? maybe 10-15 for 15 to 20 shots, maybe 20 for 60.
Last 600 match was 574-15X, 95.7%
Need to eliminate some 9's.
Wife did a 585-18X, 97.5%
I load her ammo with sorted primers

 

[Rio Precision Gunworks]

It’s been tested and proven 100x over. Primer weight variation is overwhelmingly from the compound and not the anvil or cup. Anyone claiming otherwise hasn't done any measuring of their own, payed attention to any testing done by others, and is just making up what they think and claiming people tested it.

Also, anyone suggesting the above data somehow shows the cup and anvil are the main variation of the weight needs to sit back, read more, and comment less. The average weight of the light fired primers is 3.367 and the heavy primers is 3.389. That's a bit over 99%. Conversely the average weight on non fired primers is 97% when compared.


On average, the heavy primers retained 90% of their weight and light primers retained 93% of their weight. Which makes sense for primer compound being the main difference, because the lighter primers would have a larger % of their weight in the cup and anvil.

All of this supports the weight variation is mainly in the compound. Which the velocity numbers also support.

 

[Rocketvapor]

The likely density of the crud left behind is 1/4 the density of brass.
In other words, relatively LIGHT.

 

[Rio Precision Gunworks]

Likely the most productive way to use this information is to figure out the average velocity difference per sorted unit of primer weight. Then you can see how much effect it would have on your chrono numbers.

I.E. if you normally have something like an 80es and you find that X amount of primer variation = 10fps, you could drop the high and the low primer weight and decrease your ES by 20fps.


Attempting to correlate primer weight variation into certain weights performing better........I.E. weight X has 5sd and weight Y has 10sd........will require a massive amount of data to correlate and even then, with difference variables.....may not be possible to figure out.

 

[Rocketvapor]

I find that weight bins of 0.02 grains, is easy to do (with a good scale), gives plenty in each bin out of a brick, and the extreme outliers are still trigger time.
If outlier weight relates to muzzle velocity ES, and downrange elevation, points is points.
A really good SD (and no wind) will me a higher X count, a crappy ES will likely give me 9's.
How many 9's will screw up a high X count for 60 rounds?
I get wind 9's and elevation 9's.

Besides, I'm also loading for the wife and loading fliers don't make for peace

 

[Maurygold]

I find that weight bins of 0.02 grains, is easy to do (with a good scale), gives plenty in each bin out of a brick, and the outliers are still trigger time.
If outlier weight relates to muzzle velocity ES, and downrange elevation, points is points.
A really good SD (and no wind) will me a higher X count, a crappy ES will likely give me 9's.
How many 9's will screw up a high X count for 60 rounds?

I think the issue with that is plenty of us are shooting SD well under 7 without sorting. so whether it matters materially is different than theoretically.

 

[Rocketvapor]

See, that's the difference.
Those that are Master/High Master @ 600 and 1000 aren't going to be interested in sorting if they aren't already doing it. Big cartridges are likely more forgiving as to primer effects than smaller cartridges.
Primer box color matters more than primer weight
Those that shoot worse than I do, it won't make a difference.
It's the middle of the road shooter than might gain a point or two or three.

 

[Maurygold]

See, that's the difference.
Those that are Master/High Master @ 600 and 1000 aren't going to be interested in sorting if they aren't already doing it. Big cartridges are likely more forgiving as to primer effects than smaller cartridges.
Primer box color matters more than primer weight
Those that shoot worse than I do, it won't make a difference.
It's the middle of the road shooter than might gain a point or two or three.

If you’re shooting 80 es without sorting, sorting isn’t going to vastly improve you’re reloading.

 

[Rocketvapor]

The 85ES was because I picked, ON PURPOSE, extreme outliers to TEST.
NOT my normal load.
The FASTEST heavy, shot #13 of the 30 round test was 3063fps at the muzzle (primer weight 3.730 grains).
The SLOWEST light primer #26 was 2977.4 (primer weight 3.610grains).
You would have to be pretty darn unlucky to have both of those in one relay.

Let's say I only shot the heavies (or the light ones) what was the ES and SD of the 15?
(Extreme Spread of 15 HEAVY 33.8fps SD 9.6). Still not good.
15 shots are reasonable as F-Class relays are only 20 rounds.
Just have to do that 3 times.

I need to find a brand of SRP that will NOT have a 4% spread in primer weight.

I'm looking for less than an MOA in elevation @ 600yd.
Gonnsa be hard to do with 1/2 to 3/4 MOA between light and heavy primers.

 

[Rocketmandb]

The interesting part is, if primer weight is correlated to muzzle velocity, you can by default make your chrono numbers more consistent via only using primers from the middle two or middle four weights. As you'd be eliminating higher and lower velocities on each end of the bell curve.

View attachment 8379366

At the beginning of the pandemic, when I had nothing better to do, I tested exactly what you mention. I measured a bunch of primers, then tested the ones from the middle vs the ones from the edges. The result was like a 1 SD increase for the ones from the center (from like 7 to 6, if I remember correctly). Interesting, but the juice ain't worth the squeeze.

 

[Rocketvapor]

Well, I'm retired, and I don't have nothing better to do
I'll remain one of the three shooters than sort primers.
(the other two are much better than me)

 

[hlee]

And I’m not saying you’re not removing and weighing something. I’m just saying that it means absolutely nothing.

Um...
If the loss of weight was from something other than burning of the primer compound, or was arbitrary, we might expect a lack of correlation between the unfired primer weight and the los of weight due to firing. However, that is not what we see. Graphing the data and fitting it to a linear equation gives us a very nice line with an impressive R^2 value. In fact, this is the strongest correlation in the data set. This implies that the loss of weight is not random (as the heaviest primers lost the most weight). I must assume that all of the primers that were weighed were intact- had both cup and anvil- as the lost of an anvil would throw off this implication. Anyway, I'd back away from saying it means nothing. There is something there...

When comparing the various weights to the velocities, we can see that the strongest correlation between any measured weight and a measured velocity is between the "lost weight" and the measured velocity. This follows the hypothesis, as the hypothesis is that more primer compound leads to higher velocities. An R^2 value of 0.87 is- admittedly- not terribly great, but there is clearly a correlation between the lost weight and the measured velocity. You only need to look at the clustering to come to that conclusion.

But, we don't know- a priori- the amount of primer compound that is in a primer, so this information is not terribly informative to our loading practices. That said, the correlation between the unfired primer weight to the measured velocity is nearly as strong as the lost weight is to the measured velocity (R^2=0.84). Again, one only needs to look at the clustering to see that there is a correlation between the primer weight and muzzle velocity...

I think the more interesting question- given that the extreme spread of the entire population is 86 fps, with a standard deviation of 28 fps- is "what doe the metrics look like from a population of unsorted primers?" A follow on question would be "Is the juice worth the squeeze?"

I can tell you, from my perspective, when thinking about weight sorting primers...

 

[zeroz]

Just when I think Im getting a little too far in the weeds, threads like these let me know I haven't strayed too far. I love that guys do this kind of stuff. Im realistic in my abilities and activities and thankfully neither require this.

 

[kthomas]

I would also be interested in seeing the OP test unsorted primers verse sorted primers, to see if there's any meaningful difference.

Say 30 shots from each test array.

 

[WasNH4X]

Um...
If the loss of weight was from something other than burning of the primer compound, or was arbitrary, we might expect a lack of correlation between the unfired primer weight and the los of weight due to firing. However, that is not what we see. Graphing the data and fitting it to a linear equation gives us a very nice line with an impressive R^2 value. In fact, this is the strongest correlation in the data set. This implies that the loss of weight is not random (as the heaviest primers lost the most weight). I must assume that all of the primers that were weighed were intact- had both cup and anvil- as the lost of an anvil would throw off this implication. Anyway, I'd back away from saying it means nothing. There is something there...

View attachment 8379531

When comparing the various weights to the velocities, we can see that the strongest correlation between any measured weight and a measured velocity is between the "lost weight" and the measured velocity. This follows the hypothesis, as the hypothesis is that more primer compound leads to higher velocities. An R^2 value of 0.87 is- admittedly- not terribly great, but there is clearly a correlation between the lost weight and the measured velocity. You only need to look at the clustering to come to that conclusion.

View attachment 8379538

But, we don't know- a priori- the amount of primer compound that is in a primer, so this information is not terribly informative to our loading practices. That said, the correlation between the unfired primer weight to the measured velocity is nearly as strong as the lost weight is to the measured velocity (R^2=0.84). Again, one only needs to look at the clustering to see that there is a correlation between the primer weight and muzzle velocity...

View attachment 8379540

I think the more interesting question- given that the extreme spread of the entire population is 86 fps, with a standard deviation of 28 fps- is "what doe the metrics look like from a population of unsorted primers?" A follow on question would be "Is the juice worth the squeeze?"

I can tell you, from my perspective, when thinking about weight sorting primers...

View attachment 8379544

That's for doing the above graphs/spreads........and I'll reply to yo meme with for some of us old farts .Now, if only I had a scale capable of doing so ,I'd probably jump right on down the rabbit hole with @Rocketvapor ..........just to see for myself.

 

[Rocketvapor]

@hlee
Thanks for the taking the time to run the numbers.
Strange that you can see those relationships just by looking at tabular data.
Not as precise, but it's there if you look.

The problem I see with unsorted, unless you include the entire population (1000 primers from a brick?)
Is a smaller sample of unsorted, say 100 (repeated ten times) could/would contain random numbers of middle, high and low weight primers.
A group of primarily low, or low + middle, or middle, or middle plus high, or high only would do better based on total weight range (in my eyes) than the unlucky combination of High + Low like the 30 round test I did.
Note that the worst possible combination (from available primers) was on purpose.

It would take a blind test prepared by one person and shot by another to end up knowing what was shot, and what you got. You lose a lot of data not knowing initial primer weight, or primer weight loss, to make any sense out of weight to velocity.
Unsorted gives you velocity, ES and SD, likely different with different handfuls of primers from a brick.

 

[hlee]

@hlee
Thanks for the taking the time to run the numbers.

The problem I see with unsorted, unless you include the entire population (1000 primers from a brick?)
Is a smaller sample of unsorted, say 100 (repeated ten times) could/would contain random numbers of middle, high and low weight primers.
A group of primarily low, or low + middle, or middle, or middle plus high, or high only would do better based on total range weight range if unsorted (in my eyes) than the unlucky combination of High + Low (like the 30 round test I did).
It would take a blind test prepared by one person and shot by another to end up knowing what was shot, and what you got.

Assuming that all primers weights were randomly distributed throughout the population according to their overall population density, you would expect that you would get fewer of the "edge primers" than the middle primers.

Let's create a hypothetical situation where you take the 500 primers that you weight sorted and dumped them all into a bowl. Next you stir them around to make sure that they are all well mixed. (We are instituting a postulate that mixing and stirring does not change the weights of the primers...) What is the probability that you grab a primer in the 3.62 bin? It is 11/500, or 2.2%. What is the probability of grabbing a primer from the 3.72 bin? It is 40/500 or 8%. And you have a 60% probability of getting primers from the 2 middle bins.

It is more likely that any one sleeve might skew one way or the other, or have a distribution that does not match the overall population distribution. But it is unlikely that it contains all low, or all high, or an even distribution of all weights. The distribution will tend toward the overall distribution. This is the basis of population statistics. You don't need to measure EVERY member of the population to understand the population.

But, no matter what you do, someone will say that there is not enough data and there are too many variables to draw a valid conclusion.

I'm going to caution anyone not to do too much ammo testing. You'll suck all the fun out of shooting, and then this place will be just like the rimfire forum.

 

[WasNH4X]

@Rocketvapor ......Thinkin /wonderin out loud here : Are your fired headspace numbers the same, or are there some " short" ones in the batch from known max growth? If so,I'd cull them "shorts", if ya aren't already.

 

[Rocketvapor]

Headspace? I size to a very small range.
I start with a fit check of as fired and size down until I get easy bolt lock up in an AR plus about 0.002" or easy bolt drop with a bolt gun, about 0.001" headspace.

Oh wait, you asked about fired headspace. For the test rounds I have not measured or sized them yet.
Just sitting in the range box.

We don't need the OP to run another "TEST".
What we need (or not) is someone that is a good high performance shooter to do a test.
A 1+ MOA shooter puts a lot of human variable into the data.

 

[WasNH4X]

Headspace? I size to a very small range.
I start with a fit check of as fired and size down until I get easy bolt lock up in an AR plus about 0.002" or easy bolt drop with a bolt gun, about 0.001" headspace.

Oh wait, you asked about fired headspace. For the test rounds I have not measured or sized them yet.
Just sitting in the range box.

Let's see if I can convey my thoughts in an understandable way......your fired brass is sorted per primer weight test, correct ? Your primer heavies in a batch , middle , and lite ,so forth so on. You have most/ all of your fps numbers, heavy primers running higher fps than lites ? I'd be looking for "short" fired H S in those heavy primer / highest fps brass , if any..... I'd cull to a separate pile. Would also segregate any "shorts" from mid and lite primer weights . My goal would be to keep the brass that grew to known max H S in a pile and have the "shorts" in their own pile,and work from there.Just brainstorming , suggestions that may help you reach your HM goal,........



before Flo and her bolt does ? You know if she makes HM before you,you'll never hear the end of it.
Oh ,by the way if I may ,who built the stock for Flo's rifle ?

 

[Rocketvapor]

I'll check cases before I size them.
SSS made the stock. She picked the color of the gun and I picked parts
I hope she does make master first.
Here's a better picture of her bolt gun.

 

[chevy_man]

If you want weight sorted primers just buy BR4 instead of 450s.

Here's what I shot yesterday with zero sorting. I didn't sort the brass, the primers, or the bullets.


I find it much more convenient to do load development and find a forgiving load rather than waste hours and hours with a tweezers.

 

[Rocketvapor]

What kind of brass, bullet, caliber?
I bet that's with Varget
That's tight !!

I don't think any 5 sequential shots (light or heavy) in the test had that kind of ES and SD.
Maybe the CCI450s are my problem.

 

[Maurygold]

What kind of brass, bullet, caliber?
I bet that's with Varget
That's tight !!

I don't think any 5 sequential shots (light or heavy) in the test had that kind of ES and SD.
Maybe the CCI450s are my problem.

450s are good primer and capable of low sd.