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Reloading: Is there such a thing as too much precision?

Posted on August 2, 2016
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-Greg Piet (Sin City Precision member) Photo Credit: @robert_starling

**Addendum at the bottom of this article made August 1, 2016**

 

The Story:

One of the best things since I became one of the crew here at Sin City Precision is getting together and shooting the breeze with the other folks about all things precision shooting. We have not always seen eye to eye on the best way to attack a course of fire, what reticle is the best, who makes the best glass bar-none, the best bullet, and one item where no one seems to agree on is best reloading practices.

Yes that’s right, the black art of reloading. Being an experimental physicist turned GoodWillHunting there is still a part of me where I need scientific evidence on why something is so much better than something else. With everyone having their own method, order of operation, magic case prep sizing lube, etc… there is hardly ever a time when you can directly compare between two reloaders and make quantitative comparisons.

I acquired an RCBS charge master and comparing the RCBS to my previous method of dropping a load, and trickling powder charge by hand on a $30 EBAY no name jewelers scale this thing was amazing as far as I was concerned. It was so much easier and I could get things done so much quicker. I thought I was all that and a bag of chips and there was no way I would ever need anything better.

So lets set the way back machine to a few months ago. While hanging out with some of the crew doing Cerakote work on some rigs and enjoying some adult beverages the discussion about the “Prometheus killer” came up. This “Prometheus killer” is actually the auto trickler marketed at http://www.autotrickler.com/. Now I am all for the best whizz bang widget to get the job done, but with all the variance possible in the brass itself between annealing, neck tension, wall thickness, trim length, concentricity, primer pocket fitment, bullet jump, as well as variance between primers and variance between kernels of powder I was not convinced that measuring powder charge down to the kernel was going to be a measurable variance or even remotely necessary to have some great hand loads.

A month or so later, someone in the club acquired one of these “Prometheus killers” and I wound up doing a little troubleshooting to get the thing working properly with his quite impressive lab grade scale(an A&D FX-120i). Looking at the scale it reminded me of the quality equipment I used to use for research. I just thought to myself “Self… this is complete overkill for slinging some lead down range when there are so many other external factors.” With that said the science guy started working in my wee brain and I was determined to do a test to see if having all that precision in dropping a powder charge in a bunch of different tubes of brass with each using a piece of copper and lead to cork it off was really necessary or was this super precise charge weight just some placebo making people think their hand loads were amazing thereby making them have the confidence to shoot better.

The Prep:

I decided to do my standard routine on once fired brass and load up some rounds with my RCBS, and then load some up with this fancy “Prometheus killer.” If I were to completely eliminate every other variable that would require a very controlled set of conditions and in order to satisfy my standards to eliminate every other factor I would need to measure things such as resistive forces when seating a primer as well as when seating a bullet which was not going to happen right now.

I am in no way saying this method is better or worse than any other method. Looking at the data below I would say quite the opposite as for this experiment my Standard Deviation values were garbage even by my standards. This is just for information as to what I did so you can use this to judge whether this test is bunk or not. As an example there are a number of people who believe that trimming before full length sizing is nonsense and would thereby discount this entire exercise. I am of the opinion that I would rather trim and put force and heat on the neck from cutting before I anneal, and do these cuts before I use a precision bushing to size the neck which determines neck tension between the case and the bullet. Again your mileage may vary. I haven’t won a National level match, and I am not employed by a major ammo manufacturer so what do I really know(but if they are hiring I am game if they are)?

Here is the brass/load prep for this test.

1) Decap once fired Hornady 6.5 Creedmoor brass
2) Sonic clean brass
3) Dry tumble with Lyman media (red)
4) Using air compressor to blow out all cases and ensure pockets are all clean/clear
5) Trim brass to minimum length chamfer and deburr (Frankford Arsenal)
6) Anneal brass (Annealeez machine). Junk Hornady 6.5 CM brass used to calibrate heat with Tempilaq 750DegF inside neck
7) Brass rests for at minimum 6 hours.
8) Using Hornady Unique case lube full length resize all brass using: a. Hornady Match FL resizing die b. 0.289 Redding TiN bushing for the neck c. Shoulder bump restoring it back to factory brass dimensions (which in this case is about a 0.004” bump)
9) Tumble brass in plain walnut media cleaning all lube
10) Using air compressor blow out all cases and ensure pockets are all clean/clear
11) Verify that case trim has held true
12) Prime using RCBS hand priming tool (CCI BR-2)
13) Powder charge (IMR 4451 with goal weight of 42.4gr)
14) Bullet seating (Hornady 140gr ELD-Match) COAL=2.805 and OGIVE=2.189

Now the shoulder bump this time compared to other reloads is a bit excessive. I did this for the express purpose to have the same dimensions as my control ammo (140gr factory Hornady AMAX match)

The Test:

10 rounds of factory Hornady AMAX ammo.
10 rounds loaded with the RCBS chargemaster where the weight has to have read 42.4gr
10 rounds loaded with the “Prometheus killer” where the weight has to have read 42.40gr to 42.42gr.

Using a LabRadar and a MagnetoSpeed chronometer measure the speeds of the rounds, record the SD, ES, individual speeds and all the other fun statistics I think I need. The test Rig is a Remington 700 action with a DMR LLC cut Bartlein #13 barrel 26”, a TBAC 30-P1 suppressor, Timney 510 trigger just under 2lbs, and until my other scope is in stock (c’mon Vortex where is that AMG) a Vortex Razor Gen2. On this particular rig I have not measured a definitive variance of precision with the MagnetoSpeed attached, however a side experiment will be to shoot 5 round strings getting data with both the LabRadar and Magnetospeed hooked up, then to do the same test with the Magnetospeed removed and witness any changes in groupings (both POI and group size). Those results will be released in the second installment in this series.

Results(LabRadar/Magnetospeed):

I have logged the pertinent values with the overall LabRadar values as well as the values for each string.

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LabRadar Data labeled STR1 was taken on the same shots as the MagnetoSpeed. Be cautious with the LabRadar data as a few shots were not picked up which skewed some of the statistics. After simulation using MagnetoSpeed data for the missing data statistics match up very closely.

As can be seen by the results no one load stood out as having a lower standard deviation over the other. The LabRadar data labeled “STR1” were the shots taken when both the MagnetoSpeed and the LabRadar were taking data on the same shots. Due to a missed data point on the first wave of shots with the RCBS charging method the LabRadar has a lower Standard Deviation than the MagnetoSpeed. The dubious statistical information is demonstrated by looking at the variance in the Extreme Spread between the Magnetospeed and the LabRadar STR1 data. With the loss of data running the LabRadar more merit should be put in the MagnetoSpeed data. If we were to weight the MagnetoSpeed data higher than all the LabRadar data the RCBS chargemaster somehow edged out the extremely precise Lab Scale with the super precise auto trickler. In reality however it appears that both the RCBS Chargemaster and the LabScale Autotrickler performed identically or within the statistical noise for the sample size considered.

The statistical anomalies generated due to loss of data in the LabRadar results can be explained by simulating the expected values to match or be close to the Magnetospeed data for that particular shot or by removing the one extra shot from the Magnetospeed analysis. This dramatic change in Standard Deviation by just losing one data point of five I believe is a strong indicator as to the importance of five shot groups compared to the typical three shot grouping.

Conclusion:

If I had to assess the value of a $1000 plus powder measuring setup, time saved would be a larger factor than any improved extreme spread in speed. The RCBS is quite a bit slower than just dumping a charge and letting the auto trickler finish the job if you can get the timing proper on it. I never got the timing down to make it faster and I only run one ChargeMaster so my consistency is better than those running two RCBS ChargeMasters. Based on my findings the RCBS produces adequate rounds for this particular shooter, and with my limited usage of the auto trickler I would much rather use my RCBS due to the simplicity. Depending on a rhythm you get in with reloading the time savings may or may not be worth it to get your ammo loaded up faster. I believe brass prep plays a much larger role than a kernel of powder, but brass prep will have to be addressed at a later date in a different series of articles.

The deviation in extreme spread for the two charge methods are about 10 feet per second at most. That variance is again quite small, and I believe there are many more pronounced factors that a kernel of powder. To add insult to injury for this particular series of tests it looks like the RCBS has less of an extreme spread than the Lab Scale method. For the type of shooting I do (PRS style shoots off of barricades, rooftops, ladders, etc…) that much variance is in the noise compared to how stable I am as a shooter. Since there is a measured variance it obviously does in fact make a difference, however only the individual can determine if the benefit is worth the cost and if we used these numbers as gospel you are better off using the RCBS Chargemaster over the fancy Lab Scale auto trickler.

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Raw data. Note missing values on Labradar where there is data on Magnetospeed causing variances in statistical calculations.

 

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Just the raw targets punching holes in paper. I have video and commentary denoting oddities, like the upper left target getting a pile of can mirage after two shots.

 

********** ADDENDUM / UPDATE / CROW EATING **********

Chris Tressler brought up in the nicest way the possibility of results being masked by some terrible spread in the loads. It was a perfectly reasonable assessment and something I have seen in the past. At the time of my response unfortunately I didn’t see any way to ethically sort out data to yield better information. Fortunately for me I cannot leave well enough alone and I have been in the data taking game in a past life so I actually had more information I could use to validate or invalidate my tests that I failed to consider initially. I actually marked my brass per shot so I could inspect after the fact. I’ll be honest initially all I was thinking about was ejector marks from overpressure, and I didn’t even consider anything else. When I seated the primers I thought they all felt OK and thought my once fired brass was good. As I was reflecting on my pretty awful standard deviation (even for me) I figured I should go look at what I did and figure out if there was something I fouled up. I knew the shoulder bump was on the high side, but in all honesty I couldn’t see that being the reason for the jump in values. I looked at my press, looked for issues with the die and I couldn’t find anything that was screaming out at me so I started to prep the brass to be put in the “clean me and by the way I am now twice fired” bucket in hopes that I would find something that would explain the atypically high deviation values.

I carefully inspected the brass that was shot and looked for pressure signs. The only cases that looked like they were loaded too hot and showing ejector mark signs was the factory loaded AMAX match rounds. While decapping I noticed that three cases of my hand loads popped those primers out without any force at all compared to the normal force required to pop those pesky spent primers out. For some reason I didn’t make the connection earlier as I have seen loose primers result in lower speeds. For some reason I didn’t think that my slow shots could be the result of loose primer pockets on once fired brass. Well since I knew which shots had the apparent loose primer pockets I went back to the data and omitted the shots that had potentially bad brass and let the calculations chunk through to see if that made things look “more typical” for my setup and if it would help identify a more definitive trend.

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Yeah I suck at reloading and can’t tell if a darn primer pocket is loose. Good thing I can at least document my suckage.

Shown are the data points that remained after omitting the very loose primer pocket rounds, and after that is the statistical info on the remaining rounds. I personally hate throwing out any data as I always feel like I am “cooking the books” so before I toss out data I better have a darn good reason. I this case I can say with 100% certainty I have seen loose primer pockets result in lower speeds and throw off consistency. With that said, I have no issue throwing out those three shots to see what the numbers suggest. In this particular series of tests eight of ten shots under the LabRadar were being considered (one shot was lost due to a battery issue where I never got a value), and four of five shots were being considered with the MagnetoSpeed for each loading method.

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This is much more typical of what I have seen of my hand loads. I have seen single digit values but I am normally seeing 10-15fps when I measure strings.

It looks like there is a trend showing benefit to using the LabScale method of powder charge with both pieces of measuring equipment. After the omissions the RCBS loads resulted in a SD of 14.247/11.511 on the equipment and 11.994/7.155 with the LabScale. These values are quite typical for my hand loads in the past so going by previous data it trends properly and suggests that the “bad data” was omitted. This trend suggests the LabScale method reduced the standard deviation by about 2fps worst case. In addition the extreme spread was only reduced by 4fps when considering all the remaining data points (meaning using the LabRadar data). The MagnetoSpeed data makes the LabScale method even better however it only has half the sample size. As a way to emphasize how small of a factor this powder charge difference is look at the NON MagnetoSpeed data (STR2) for both the RCBS and the LabScale and you can see the SD favors the RCBS and the ES is the same.

So if I can trust the reasoning for removal of a few data points, the LabScale does help ever so slightly in making a more accurate round. Only an individual hand loader can determine if they are detail oriented enough in all their other methodology to make the very careful powder charging method down to the kernel beneficial. Personally, if I can let loose primers get through and skew the data here, I obviously am not skilled enough on a regular basis to warrant such a precise method for charge weight as the LabScale method.

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