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 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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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!