In the first part of this series, I spent a significant amount of time and energy measuring several dimensions of the same rifle cases, over and over for five firings. The goal was simple -- to measure the relationship between the weight and volume of the cases. The theory-first approach I took does have its merits, but admittedly the results were a bit less clear.

Another valid way to approach this experiment is results-focused. To simply record the performance (muzzle velocity, score, etc) of each case, look for outliers, then try to better understand why they are outliers.

The same obstacle that prevents either method from being practical. Namely, a reliable way to keep track each and every rifle casing throughout several rounds of firing, cleaning, and reloading. My solution to this problem? Microstamping.

As usual, the raw datasets are available on GitHub.

Microstamped precision rifle cases Microstamped precision rifle cases

Overview

The charts in my previous article about sorting rifle brass, which showed how the dimensions of each case changed over the course of several firings, gained a lot of attention from readers. Besides being time-consuming, the biggest challenge was simply maintaining the order of each case. When I finally trimmed the cases to length after the third firing, I realized that I had finally messed them up. While my mistake didn't ruin the experiment, I would need to solve that problem going forward.

What I wanted was a way to permanently mark each case with a number. Sharpie markers and paint pens won't withstand the cleaning process of wet tumbling with stainless steel pins. Finally, it dawned on me -- microstamps! Sure enough, I found a company in California that manufactures a reasonably-priced jewelers microstamp made from hardened steel for marking 1mm tall numerals, perfect for stamping brass.

I couldn't find anyone who has used this technique before, which tells me that we're breaking new ground. Interestingly, the top search results for microstamping do relate to firearms, but as they pertain to laws and restrictions in states like California. Having lived there for a decade, I'm very familiar with those issues -- this article isn't about that and I'm not here to discuss politics.

Why Bother Microstamping Brass?

The goal of microstamping your brass isn't to let you easily identify your brass from someone else's. The goal is to aid your load development and give you a competitive edge with the next level of insight into how your ammunition performs.

How, you ask? Microstamping your brass eliminates a variable from your load development that you may not have considered. If you can't correlate your velocity data to each individual piece of brass then you're randomizing the only reusable component during your tests.

Consider if you were to sort your rifle brass by weight (lightest to heaviest), volume (least to most capacity), or just beauty (prettiest to ugliest). Now, if you were to stamp those cases, you can be certain which ones you're using in your load testing or matches. You can always fire them in the same order that they were sorted, or some other order that suits your needs. You can track the velocity, chamber pressure, or performance of each case is over their lifespan. The list goes on.

Pros & Cons of Microstamping

Right off the bat I'll tell you that if you're the kind of person who prefers the extra-large gauges in your Buick or writing in ALL CAPS because it's easier on your eyes -- this technique isn't for you. I'm 40 years old, colorblind, nearsighted, and am still personally able to read these 1mm microstamps. The manufacturer is kind enough to include a loupe, which makes it even easier, as does a well-lit room. The point is that they can be difficult to read for some folks and I'd rather not get a bunch of angry emails from disgruntled readers, especially in ALL CAPS.

That said, here are a few quick pros/cons of microstamping.

Pros:

  • Maintains case order, with or without sorting
  • Survives wet/stainless tumbling
  • Gained insight into individual case performance

Cons:

  • Stamping process is time consuming
  • Stamps can be difficult to read for some people
  • The stamping tool may be considered too expensive by some

24 Hours of Lemi Shine

Before I stamped hundreds of cases, I wanted to be certain that this tool would mark deep enough to still be readable after several sessions of wet tumbling with stainless steel pins. To simulate that, I tumbled a few test cases for 24 hours straight. I usually tumble cases for about 2 hours, so this is equivalent to 12 reloads on each case which may be beyond their actual useful lifespan. Below are some before & after photos of those cases in which you can clearly see that the stamps held up beautifully.

Hornady 6.5mm Creedmoor case microstamped with `04`, before and after 24 hours of wet tumbling with stainless steel media. Hornady 6.5mm Creedmoor case microstamped with 04, before and after 24 hours of wet tumbling with stainless steel media.

Lake City .223 Remington case microstamped with `5` and `7`, before and after 24 hours of wet tumbling with stainless steel media. Lake City .223 Remington case microstamped with 5 and 7, before and after 24 hours of wet tumbling with stainless steel media.

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How I Stamped 250 Cases

Since I operate Ammolytics in my spare time on a shoestring budget, I convinced a fellow competitive marksman to purchase one for himself and he was kind enough to loan it to me. (Thanks, David!) I tried marking different parts of the case on both 6.5mm Creedmoor and .233 Remington cases and finally decided that marking the bottom of the case was the best option for a few reasons:

  • The manufacture stamp was already there, so there was little risk of compromising the case
  • Easier to hold it in place for stamping
  • There's usually enough empty space to add two digits
  • It'd be easy to sort the cases when they were placed upside down on a reloading tray or in the box

Then it was time to stamp the cases that I'd be experimenting with, 250 cases in total.

  • 50 used Peterson cases
  • 100 new Peterson cases
  • 100 new Lapua

This was far too many to mess around with hand tools and hammers, so I rigged up an automatic punch adapter, then I built a simple jig with my drill press. A gauge pin in a vise would position each case and the automatic pinch was held in the drill press chuck. The operation would be fairly straightforward -- drop a case onto the pin, set the correct stamp number, and pull down the drill press handle to stamp the brass.

Microstamping tool with a shop-built adapter for an automatic punch. Microstamping tool with a shop-built adapter for an automatic punch.

Drill press microstamping jig. Not very skookum. Drill press microstamping jig. Not very skookum.

It wasn't perfect.

  • The pin I used was an intentionally sloppy fit so that I could have some wiggle room for correcting the stamp placement.
  • The automatic punch didn't fit very well into the chuck which meant the automatic spring mechanism started to get finicky.
  • At one point, I was just using pressure to stamp the brass instead of the punch's hammering mechanism.

Regardless, it was much faster and less error prone than stamping by hand and I got through them all.

The case heads were indexed and marked 00 through 99. You can see the results in the following photo, which I took using a flatbed scanner.

50 microstamped case heads of Peterson  6.5mm Creedmoor brass. 50 microstamped case heads of Peterson 6.5mm Creedmoor brass.

As an aside, I've been experimenting with a flatbed scanner as an optical comparator. The idea is to quickly and easily measure case mouth diameter, concentricity, and neck thickness using image analysis & quantification software instead of calipers and micrometers. It's a heck of a lot faster, since you could can scan 100 cases or more at once and let the software do the work for you. More on that in a future article -- I'm still working on it. Have I mentioned that you can support my work through Patreon?

Per-Case Performance Metrics

Since stamping the original batch of 6.5mm Creedmoor cases I've only fired them twice, each time using my standard load, a MagnetoSpeed V3, and a ShotMarker target at 600 yards. The following charts provide interesting observations, even if it's not much data to draw any conclusions.

The two days on which I fired these rounds were three months and 24°F apart, which may account for the faster average muzzle velocity.

Note: Case 42 was damaged and is omitted from the dataset.

Muzzle Velocity Comparison

There's other data to consider which is not captured by these charts, such as the amount of time the barrel was allowed to cool between each shot and each string. As I've observed in other experiments, the velocity tends to increase as the barrel heats up.

per-case muzzle velocity comparison

bar_chartOpen Interactive Chart

Target Velocity Comparison

per-case target velocity comparison

bar_chartOpen Interactive Chart

Note: The maker of the ShotMarker target does not publish any details about the accuracy or precision of the velocity data it reports, so these values should not be given too much weight.

Per-Case Muzzle and Target Velocity Table

2020-02-15 2020-05-17 Mean Delta
Case Muzzle (ft/s) Target (ft/s) Muzzle (ft/s) Target (ft/s) Muzzle (ft/s) Target (ft/s) Muzzle (ft/s) Target (ft/s)
127321912275619272744.01919.52415
227351872277219462753.51909.03774
327271893276719592747.01926.04066
427391908275819282748.51918.01920
527301904276419512747.01927.53447
627261882275819412742.01911.53259
727331916277719502755.01933.04434
827421886277719572759.51921.53571
927461892277819642762.01928.03272
1027411891277619672758.51929.03576
1127491910277119492760.01929.52239
1227411905278119512761.01928.04046
1327381883277019652754.01924.03282
1427441904276519482754.51926.02144
1527431906276519552754.01930.52249
1627321918275719222744.51920.0254
1727371887277719442757.01915.54057
1827271877277019292748.51903.04352
1927351899277019372752.51918.03538
2027241893277219622748.01927.54869
2127371906276819582752.51932.03152
2227331881277619522754.51916.54371
2327571898277419422765.51920.01744
2427401918276319322751.51925.02314
2527451912278419522764.51932.03940
2627231903277219342747.51918.54931
2727321893276719462749.51919.53553
2827401870277919502759.51910.03980
2927251895278219512753.51923.05756
3027351895277619552755.51925.04160
3127361902278319642759.51933.04762
3227331876278919472761.01911.55671
3327251894278919562757.01925.06462
3427301890278319642756.51927.05374
3527291894276919552749.01924.54061
3627281871278119512754.51911.05380
3727341919279119632762.51941.05744
3827301885277619362753.01910.54651
3927191890278019462749.51918.06156
4027401906279119632765.51934.55157
4127301882277719642753.51923.04782
4327281881277419302751.01905.54649
4427281869278919632758.51916.06194
4527321901279219602762.01930.56059
4627351885278919582762.01921.55473
4727441908278519572764.51932.54149
4827281887278819562758.01921.56069
4927271899278919572758.01928.06258
5027341899278319482758.51923.54949
Mean 2734.2 1894.8 2775.9 1950.2 2755.1 1922.5 41.7 55.4
Median 2733.0 1894.0 2776.0 1951.0 2754.5 1923.5 41.0 57.0
Std Dev 7.5 13.3 9.7 11.5 5.9 8.1 12.7 18.9
Min 2719.0 1869.0 2756.0 1922.0 2742.0 1903.0 17.0 4.0
Max 2757.0 1919.0 2792.0 1967.0 2765.5 1941.0 64.0 94.0
Range 38.0 50.0 36.0 45.0 23.5 38.0 47.0 90.0

Next Steps

This is the second in a series of brass sorting experiments, which I'll continue to explore. Be sure to subscribe to the mailing list below or follow on your social media platform of choice to be notified when the next one comes out.

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    Have you done something similar, or have per-case data that you'd like to share? I'd love to hear from you!
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References


Special thanks

  • To David Christian for the use of his microstamp kit.
  • To Rick Burton and the rest of my Patrons, for their continued support which allows me to do this work.

Before you go...

Thanks for taking the time to read this article! I enjoyed writing it and learned a lot in this process and I hope that you did too. If you have any feedback, you can email me directly if you don't prefer to use Reddit or other social media.