Gunwerks 300 Winchester Magnum Brass Review

Gunwerks 300 Winchester Magnum Brass Review

As I scrolled through my inbox one morning, an email from Gunwerks popped up. The subject line read: Introducing Premium Rifle Brass from Gunwerks. I clicked on the link and was pleased to see 300 Winchester Magnum on the list of offered cartridges.

A week later, a box wrapped with the familiar Gunwerks tape landed on my porch. Inside was a heavy plastic bag full of shiny 300 Winchester Magnum cases. Gunwerks advertises their brass coming in a reusable, zippered pouch. Unfortunately, they had a shortage of those pouches when I ordered mine. No big deal for me; my brass rides around in 50-round MTM cases anyway.

Gunwerks 300WM Rifle Brass

Gunwerks sells their brass 100 pieces at a time, which will set you back $109 for 300WM. I periodically checked availability during this review, and always found it in stock.

The first thing I did was count the cases and look them over carefully to be sure I could use them all. Because they’re shipped loose, it didn’t surprise me that the case mouths had some slight dings and dents. But they didn’t have crushed necks or dented shoulders. A quick pass over an expander mandrel would fix them right up and set the initial neck diameter.

The case bodies showed a distinct anneal line ¼” up from the shoulder, and none were dented or blemished. The case heads, extractor grooves, and primer flash holes looked uniform and free of defects. Gunwerks brass is manufactured with minimal headstamp markings to help identify pressure signs, such as ejector marks.

Before you ask– I don’t know who manufactures the brass for Gunwerks. All I know is Gunwerks engineered the specs and provided the tooling.

The next round of testing included a weight variation check. For this review, I decided to record the weight of each case, rather than sort them in batches.

In New Brass Prep for Long Range Reloading, I outline my procedure for preparing new brass for the first firing. One of the steps is to weigh the entire batch, sorting cases into piles of like weights. I usually cull the pieces that vary more than 1% from the average weight. Do I think it makes a difference? Not that I’ve seen, but weight variation is good data for a brass review, so I fired up the scale and sharpened my pencil.

Gunwerks Brass Weight Variation Test

The median weight of this batch of Gunwerks 300 Winchester Magnum brass was 249.7 grains. The heaviest piece weighed 251.6; the lowest came in at 248.1 grains. Neither extreme exceeded 1% of the average weight of 249.3 grains. Most of them weighed within .5% of the average—89% of them to be exact.

I weighed the cases straight from the bag, rather than after any initial prep work, including trimming. It’s been my experience that small weight variations tend to tighten up after that work is done.

The next thing I did was mostly out of curiosity. I cross-sectioned three 300WM cases; one each from Atlas Development Group (ADG), Gunwerks, and Winchester (WW). The ADG and Gunwerks brass looked very similar in appearance and manufacture. The biggest differences the WW brass showed was the lack of a visible anneal line and the design of the primer flash hole.

Cross -sectioned Gunwerks 300WM Case

I cross-sectioned a piece of Gunwerks 300WM brass out of curiosity.

The flash holes in Gunwerks brass are not drilled. Despite that, they appear to be uniform, with no burrs on the combustion side.

The case wall thickness of the Gunwerks 300WM brass was very consistent. I checked a handful of cases with a tube micrometer, then spun up the rest on a Sinclair Case Neck Sorting Tool.

Before I could check for case thickness variation, I had to clean up the dented necks. I used my Redding Type S FL bushing die with a .333” steel bushing and polished expander button to iron out them out. I normally use a Sinclair expander die with mandrel for this, but the sizing die worked just fine.

Gunwerks 300WM Brass Neck Thickness

Checking case wall thickness with a Mitutoyo ball micrometer.

The tube mic showed thickness measurements of .0135”-.0140” while checking at four locations on several cases. A few of them measured .0135” all the way around.

Gunwerks brass test with Sinclair tool

Checking for neck thickness runout with a Sinclair Case Neck Sorting Tool.

The rest of the cases were checked on the Sinclair Case Neck Sorting Tool. This tool is handy for checking large quantities of cases for thickness variations. Most of the cases barely caused a flutter on the dial indicator. I noted eight cases that showed .001” runout.

A common question asked is, “How many times can a case be fired before it needs to be replaced?” I decided to put one piece of Gunwerks 300WM brass through a torture test as part of this review.

All test firing for this review was done with a custom rifle built for long-range shooting. The specs on the rifle can be found HERE. The barrel had 720 rounds through it when testing began, with a record of excellent long-range accuracy. My standard load for this rifle uses Winchester (WW) brass to shoot 210-grain Berger HVLDs at 2980 fps. That brass was on its eighth and ninth firings, but still performing well.

I selected the new case at random, recorded all dimensions, and checked max capacity with H1000. Using a 12” drop tube, I was able to stuff 89.0 grains of H1000 into the new piece of Gunwerks 300WM brass. That was only half a grain less than max fill on a new piece of WW brass.

I reduced my normal load of 77.5 grains of H1000 by one full grain (76.5) and seated a 210-grain HVLD .010” off the lands. The first firing produced 2965 fps over the Magnetospeed with no signs of excess pressure. I recorded all fired case dimensions, then full-length sized the case and duplicated the load.

Using fired brass, the next shot mirrored the new case test at 2963 fps with no pressure signs. The case capacity had also grown to 92.0 grains of H1000.

On the third firing, I loaded 77.0 grains of H1000 into the Gunwerks case. That load produced the same speed (2977 fps) as my standard load of 77.5 in WW brass, with no pressure signs. I full-length sized it again and increased the charge to 77.5 grains of H1000.

The fourth shot clocked 3002 fps, with no heavy bolt lift, and no ejector mark on the case head. The next 16 shots were fired with the same recipe, for a total of 20 firing cycles on a single Gunwerks 300WM case.

Even though there was nothing wrong it, I stopped testing at 20 cycles; mostly because it seemed like a good number to stop at. In the real world, most shooters aren’t going to cycle through a single piece of 300WM brass 20 times.

Gunwerks Headstamp Pressure Signs

Slight ejector marks during the torture test. Gunwerks designed the case head to help identify pressure signs.

I felt confident that I’d tested the case at, or near the max load for my chamber. In fact, shots 9 through 11 showed light ejector marks. I believe that was due to the neck hardening, because they disappeared after annealing the case.

As monotonous as it was to reload—shoot–repeat 20 times over the course of two days, it did provide some good data. Here are some of the more interesting findings, as well as data pertinent to this review.
  • The primer pocket diameter of a new Gunwerks 300WM case is .208”. The 20x-fired case’s pocket measured .2085”. SAAMI spec is .210” MAX, which is the diameter of a CCI 250. There was no discernable difference in “feel” when seating primers, from the first firing to the last.
  • The test piece weighed 249.2 grains when new, 248.8 after the first firing/size/trim cycle, and 248.4 at the end of the test period.
  • The muzzle velocities for all 20 shots, in order of firing: 2965, 2963, 2977, 3002, 2996, 3008, 3010, 3005, 3010, 3015, 3012, 2995, 3003, 3000, 3005, 2998, 2995, 2998, 3008, 3005.
  • I didn’t anneal the case until after shot #11. I could feel a difference in sizing and seating resistance on shots 10 and 11 and noticed a rise in muzzle velocity. After annealing the case, it stabilized for shots 12 through 20. In my experience, Winchester 300WM brass requires annealing soon and often after the first firing for good performance.
  • The new case shoulder length grew by .020” in my chamber. After that, stretch was limited by full length sizing with a .002” shoulder setback.
  • The OAL of the new case measured 2.620” and grew only .002” in the first firing. I trimmed it to 2.615”. By the fourth firing, it had again grown to 2.620”. That cycle continued for all 20 shots, with the case OAL growing by .001” during each cycle of firing/sizing.
300WM Velocity Testing

Range time during the test period.

The data showed that I could use Gunwerks 300WM brass as a direct replacement for WW brass in my rifle. I loaded up the 98 remaining new cases with the same recipe I used for the test piece.

The load is 77.5 grains of H1000, a CCI 250 primer, and a Berger 210 Hunting VLD seated at 3.560” COAL. That seating depth jumps the VLD .010” before contacting the lands in my barrel. This load is the max load in my barrel using these components. During the initial load development with WW brass, I started at 75.0 grains and worked up in ½ grain increments. Be sure to do the same if you want to try this load.

Long range 300WM

Making once-fired Gunwerks 300WM brass at 1756 yards.

After confirming the muzzle velocity with the max load and new brass, we headed to the mountains for some long-range shooting. I adjusted the muzzle velocity in my Kestrel and started picking off targets out to 950 yards. With corrections lining up and accuracy on par, we pushed out quickly to a 1.5 MOA target at 1756 yards. My son, Jake and I scored 18 hits out of the 25 shots we took at it. Almost every miss was due to poor wind calling. The lack of vertical dispersion was very impressive.

G7 BR2500 1756 Yards

Over the next two weeks, we turned all the new brass into fired brass. Jake even logged his first 2k+ shot with the 300WM, connecting on a 1 MOA target at 2320 yards. That’s right at the limit for us and our equipment, and impressive performance from ammo loaded in new brass.

The Gunwerks 300WM cases used in this review are now on their fourth firing. We continue to enjoy excellent accuracy, single-digit velocity E.S., and consistent performance at long range.

I’m not one to claim that you need premium brass to get good results. There was a time in the not too distant past, when premium quality brass was in short supply, or non-existent for many cartridges. Those cases could be sorted and massaged to provide excellent results downrange. But it was time consuming, wasteful, and rarely consistent.

The cartridge case is the foundation for the loaded round and starting out with a perfect one reduces or eliminates a lot of variables. Not counting the primer, the case is also the least expensive component used in the long run.

Gunwerks brass review

The thing I liked best about this Gunwerks 300WM brass was that I could use it as a direct replacement for WW brass in my rifle. Its consistent wall thickness, uniform primer pockets, smooth flash holes, and annealed necks eliminated a bunch of prep time. It offered the same performance when new, that the WW brass took hours of prep time to achieve and maintain. I also believe it will last longer.

The only things that surprised me were the dinged necks and the large overall number of different case weights, even though they were relatively close. Neither affected performance, but they seemed out of place with high-quality brass. It’s worth noting that I always run an expander over new brass, regardless of the condition of the case mouth. Even on perfectly round necks, I’ve never worked with a piece of brass that didn’t need an adjustment for initial neck tension.

Sam Millard Testing Gunwerks 300WM Brass

Gunwerks states their brass is “designed to be the perfect brass for precision shooters.” I found it to be excellent brass for my 300 Winchester Magnum, and won’t hesitate to use it in my next barrel. I highly recommend it to anyone looking for premium quality brass for their next project. Click HERE to order yours!



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As an Idaho native, avid hunter, and long range shooter, Sam has written numerous articles and gear reviews for various online publications. Specializing in long range hunting in the mountains of northern Idaho, Sam founded Panhandle Precision as a way to continue sharing his passions.

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  • R2rr
    January 10, 2019 at 14:34

    Beautiful write up. Hopefully Gunwerks will read it and at the VERY least, send you replacement cases for those you sectioned.
    You know they will make more sales from your write up.

  • John B.
    January 10, 2019 at 18:11

    Excellent review on Gunwerks brass. The detail you put in your review made the difference for me. Keep up the good work.

  • Tom Dsvies
    January 10, 2019 at 18:12

    What is that tripod and saddle?

  • stefano
    January 11, 2019 at 06:54

    Ottima recensione ,tutti i tuoi articoli hanno migliorato di molto le mie prestazioni con il 300 win mag.
    buon lavoro e grazie..

  • Stephen Spjut
    January 11, 2019 at 11:17

    As always Sam your review is chalked full of just the right info. I’ve been using Federal brass for some time now with H1000 #250 primers and 230 Berger tactical hybrid. Although the load flies fast and true the brass wears out quickly and must be annealed every third firing. Once my Federal brass is toast I will definitely switch over.

  • Bill
    January 12, 2019 at 13:42

    Great write up Sam,
    The review was extremely thorough and has me thinking! I will be doing load development soon for a 300 WM that shawn just finished up for me. I have loaded for belted mags alot over the years, but it has been alot of years since I have began load development on one, starting with only new brass. You reached your 77.5 gr load on a piece of brass with 4 firings on it, at 3002 fps. Then you loaded up the remaining 98. What was the velocity on the 98 virgin cases at this load? It sounded like it was very close to the 3002, is that correct? Also, how many firings did it take for the case shoulder to blow all the way out to the chamber to the point where you had to start pushing the shoulder back .001 to .002? To sum it all up, did you notice a velocity or pressure difference from the virgin case versus cases as they were growing to the chamber length, versus a case that finally reached chamber length? My plan is to load 10 to 15 virgin cases at a starting load to complete a barrel break in. Then, run a quick pressure test to find max, using one round each moving up .5 grains at a time. Then back off of max and shoot for groups. In the past, I have been successful doing all of this with virgin brass. Since the belted cases tend to grow approx 20 thou before reaching chamber length, I was thinking that I would need to use brass that has reached chamber length to do the pressure testing. What are your thoughts on this?

    • Sam
      Sam Millard
      January 13, 2019 at 07:50

      The only time I checked for velocity or pressure difference between a new case and fired case was on the test piece. It was 2 fps with the same load, from new to fired. All fired case dimensions were identical from the first firing to the 20th. Random checks on the rest of the batch while sizing were identical to the test piece. I made one run over the chrono when the rest of the brass was still new, which showed 2999 fps as the avg. MV, with 12 ES.

  • Bill
    January 12, 2019 at 17:24

    Sam, I just read through my notes and thought of another question. I am using norma brass (wish I would have read this review first). My loaded rounds measured .335 to .335.5, so I went with a .334 bushing. To prep the brass as you described, I used my type s bushing die with the expander button installed. However, after running them through the expander die, the OD measured .333. Since this smaller than my .334 bushing, the bushing didn’t touch the case. Did you run into this when you used the expander button in this step?

  • Steven Johnson
    January 13, 2019 at 07:35

    Hi Sam! Awesome review.
    I ordered 100 pcs of Gunwerks 6.5 Creedmoor brass and did a similar ‘upon receipt’ review as you. The numbers were very similar to the .300 WM. However, I received only 99 pieces of brass and about 10% had significant neck deformations and probably half had visually out of round necks. I seated and pulled a bullet from all 99 and resized with a .291″ Redding bushing to get rid of the kinks and dents. I reamed and chamfered all 99. That’s the sum total of ‘issues’ from me. I’ll load some 147 ELD M over H4350 and shoot those from my Bergara B14 HMR. I expect great results from here on with this brass.

  • Bill
    January 13, 2019 at 08:42

    Thanks for the replies Sam.

  • Anthony
    February 11, 2019 at 00:31

    Thank you for taking the time to do a review on the brass. Gunwerks seems to offer great brass for the money. Your test results are appreciated and again everyone thanks you. Keep those reviews coming!

  • Rick Rydalch
    February 24, 2019 at 19:29

    Great review I got a question. Where you already had a load developed in another brand of brass did you have to first fire form all of them? Did you have to fine tune your previous load development?

    • Sam
      Sam Millard
      February 25, 2019 at 05:25

      Accuracy improved a little bit from new to fired brass, but the load stayed the same. When I switched from WW to GW brass, the max load was .5 grains of H1000 lower than it was with WW when the barrel was new. Not much difference at all.

  • Nick T
    October 17, 2019 at 06:40

    Sam, big fan of all your video’s and all the info you provide. I bought this same gunwerks brass for my 300wm, after loading a 208gr eldm I got a measurement of .336 neck O.D. After reading your article I jumped the gun and bought the .333 bushing.
    Does this mean that the gunwerks brass is different from lot to lot?

    Thanks for all the info

    • Sam
      Sam Millard
      October 17, 2019 at 07:11

      Not that I know of. Mine measure .335″ with a 210 VLD. ELDs tend to run a little fat, so maybe that’s where some of it is coming from? Even so, you should have no problem with a 333 bushing, especially if you’re using the die’s expander.

        October 19, 2019 at 07:00

        Thanks again,
        I take the expander out and use the sinclair mandrel
        In an extra step.

  • Bernard Vance
    December 8, 2019 at 10:02

    Terrific write up on this brass. I was going to spring for RWS brass for the .300 WM I just finished building but I’m now considering the Gunwerks brass and saving myself some money. Your website and videos have been a tremendous help! Thanks for all your hard work from a neighbor over here in Kalispell.

  • alan n. sayre
    January 9, 2020 at 18:04

    Thanks for a great review. I just measured the Gunwerks brass. There were 102 piesces ave = 251.44 sd 0.70 spread 4.0 gr. removing the single heavies 3.5

  • alan n. sayre
    January 9, 2020 at 18:12

    Also two cases were dented. A little more care in handling should be shown. Boxing them up like Norma would be better than the G bag.

  • ken creager
    January 10, 2020 at 10:54

    this was an awesome review, i was really wondering about how many firings you might get. I’ve done some measuring and it seemed the Gunwerks Brass is premium brass.

  • Josh Page
    February 1, 2020 at 17:34

    Great review Sam. I’ve been looking at their brass and had been considering ordering some up. I think I will give them a try.

  • Aaron
    February 23, 2020 at 20:04

    Sam- I just purchased some of this brass for my 300WM. Did you use a Redding Type S Bushing die for sizing? What size bushing do you recommend? I am going to try 215 Berger Hybrids and 210 Accubond LR with H1000.

  • Brian
    May 18, 2020 at 10:31

    In the picture of the case head, you show slight ejector marks. Is that amount of marking substantial enough for you to reduce your load, or do you live with that?

    • Sam
      Sam Millard
      May 19, 2020 at 04:46

      I would back off a load that showed any ejector marks on the case head.

  • Tim Sanders
    February 7, 2021 at 19:52

    Very interesting review. From what I’ve read Gunwerks does buy their brass from ADG, who by the way packages their brass in plastic boxes similar to Lapua.

  • Mica Bodenheimer
    August 22, 2022 at 10:16

    Times at Gunwerks must be changing. I ordered 100 once fired 7mm Rem Mag and got a bag of the dirtiest brass I’ve ever seen. Like shot out of a auto loader dirty. I was pretty surprised, I’m actually wondering if it’s actually only once fired the way it looks.


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