300 Winchester Magnum Headstamp

New Brass Prep for Long Range Reloading

The process of reloading fired brass gets a lot of attention, but what about new brass prep? As part of the 300 Winchester Magnum Project, this article will cover how I prepare new, unfired cases.

I’ve tested most of my process for its rate of return in performance. Admittedly, there are still some things I do during new brass prep that are hard to justify. I’ll point them out as I come to them. The first thing I do is start with an appropriate number of new cases. I never recycle fired cases from old barrels into new projects. For my long range hunting rifles I’ll usually start with 100 -200 new pieces of brass from the same lot. For the 300 WM, I’ll prep 100 pieces of Winchester (WW) brand brass.

Not all cartridge brass is created equal. The process I use for new brass prep will vary accordingly.

It seems like every brass case manufacturer does things a little differently. All cases start out as a brass cup that is formed to the dimensions of a cartridge case, but the hardness of the brass and finish quality differs greatly across brands. It can also vary in thickness, causing a disparity in case volume from brand to brand, as well as from different lots of the same brand. This is an important consideration when developing a load. Depending on the powder used, case volume variations can greatly influence pressure and velocity. If you’re trying someone else’s load, find out what brass they’re using. WW brass tends to be thinner than others, allowing more interior space for powder. Unfortunately, it tends to be pretty rough out of the bag.

The first step is to visually inspect each case.

I inspect each case for dents in the shoulder, splits in the neck, and primer flash holes that are punched off-center. Also, I take a look at the extractor rim to make sure it was cut with enough clearance. I’m not measuring anything yet, just trying to avoid unnecessary work on brass that will be tossed anyway. Out of the 100 pieces, 97 passed the initial inspection. The three culled pieces will be used for setting up tooling or adjusting the annealing machine.

WW 300 Winchester Magnum Brass

WW brand 300 Winchester Magnum brass.

New brass prep for long range reloading

This is what most of the case necks looked like.

The next step of new brass prep is getting the case necks squared away.

The necks on this WW brass looked like a bunch of elves worked their way into the bags and beat on them with hammers. They were pretty banged up. However, even with straight necks they would need some attention. Now is the time to set the neck diameter for the desired tension on the bullet. Depending on what dies you’re using, this could be as simple as lubing the case necks and cycling them through the die. The expander ball will straighten out the inside of the neck, and the die or bushing will set the tension. Redding’s Competition Die Set has no provision for expanding case necks, so I used a dedicated expander die. It’s a Sinclair expander die that uses tapered mandrels sized to a specific caliber. I dipped the case necks in Imperial Application Media coated with dry neck lube, ran the case over the expander mandrel, then rotated the Redding T-7 turret and sized the neck with the Redding Competition Neck Die. I wanted to experiment with a very light neck tension for the initial load development, so I used a .334” steel bushing in the die. The easiest way to determine bushing size is to load a dummy round with the bullet you plan to use. Measure the loaded outside diameter of the neck, then subtract how much tension you want. The loaded diameter on mine was .3345”-.3350”. That’s pretty light compared to the .001-.003” I usually use, but I want to see what happens. I have a .333” bushing on hand if I decide to increase the tension.

New brass prep with a Redding T-7

Redding T-7 press loaded with both dies.

New brass prep with Sinclair expander die

Sinclair expander die with .30 mandrel.

Trim each case to a uniform length, then chamfer and deburr the mouth.

This step can seem meaningless because the cases will most likely be short enough, but consistency rules all in long range shooting, so I trim every case. If you have plans to turn the necks for uniform thickness, they will have to be trimmed first. I don’t worry about a specified length. I just want them all the same length and not too long for the chamber. I use a Wilson lathe-type trimmer. I trimmed the cases to 2.610”.

Two of those hard-to-justify steps are cleaning up the primer pocket and primer flash hole.

Early on in my reloading career, I had a problem with primers not seating fully in some Remington brass. I discovered the pockets were too shallow, so I found a tool that allowed me to cut those pockets to the proper depth. I can’t tell you if it makes any difference at all to the performance of the loaded round. I also can’t remember the brand of the tool, but it has adjustable cutters for large and small pockets, and makes a great pocket cleaner for fired brass cleanup.

Another dubious operation is cleaning up the primer flash holes. This hole is punched in WW brass, rather than drilled. The process leaves a chunk of brass hanging inside the case. I have found that knocking that chunk of brass out of there helps keep tumbling media from sticking in the case. Other than that, I haven’t been able to prove its worth.

Both of those steps are “one and done”, meaning they never have to be repeated. For the record, the amount of brass I removed from each of the 97 cases weighed .8 grains on average. Something to keep in mind if you want to weigh cases.

Primer Pocket Uniforming Tools

Flash hole deburring tool and pocket cutter.

New brass prep includes uniforming the primer pocket

Adjustable carbide cutter.

Weigh the cases?

I think it’s a waste of time. I really do. I still do it, but mostly to get a feel for the consistency of the brass. I used to toss brass that deviated more than 1% from the average weight. A surprising number of cases from this lot of WW weighed exactly 240.1 grains. There were only three that failed. They weighed 243, 243.2, and 244 grains. I set them aside for further experimentation. The whole point of weighing is to compare volume from case to case, but how much difference does it make? I’ve found that if I use cases of the same brand, from the same lot, and keep the ones that weigh within 1% of each other, I will end up with good ammo. Usually when I find one that is way outside the norm, it fails the next test big time.

I don’t turn necks, but I check them for runout during new brass prep.

I use a Sinclair Case Neck Sorting Tool to check neck thickness runout. It uses a stem that protrudes through the flash hole and a mandrel that supports the neck. A dial indicator measures the neck thickness runout as the case is spun on the stem. If it’s over .003”, I set that case aside to be used for tooling setup or testing. I tried a ball micrometer, but that proved to be too tedious for me.

I tried neck turning a couple of times. Once on an extremely accurate 260 Remington using Remington brass, and again on a 7WSM with Winchester brass. Both times, I turned the necks to approximately 75% contact, which gave them less than .001” runout. Neither rifle showed an increase in accuracy or a decrease in velocity E.S. or S.D. In fact, I mixed the turned cases in with the un-turned cases and used them together with no discernible affects. I would use neck turning as a diagnostic tool perhaps, but won’t turn them just because it’s supposed to help.

Case Neck Thickness Comparator

Checking case necks with a Sinclair neck thickness comparator.


This is where reloading data for the project starts. I measure everything during new brass prep and keep careful notes.

Keeping careful notes is an integral part of successful reloading. How else will we know what works and what doesn’t? I keep Post-it note pads scattered around my reloading room for quick notes and a journal to transfer them into later. In addition to recording the steps already mentioned, I also measure the case’s shoulder to head length and the web diameter. These measurements will give me an idea of what the chamber looks like and how much the case is stretching. As this project continues, the journal will fill up with component specs, seating depths, and target data. It will allow me to duplicate my good loads and at least have a starting point for the next project.

That’s it! Time to start pouring powder and seating bullets. I encourage you to try my new brass prep techniques, but feel free to question and test them for efficiency on your next project. You may find some areas that can be tuned for your specific needs. With long range reloading, all that matters is downrange performance. Check out my YouTube channel for detailed reloading videos. 


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  • Casey
    March 5, 2016 at 09:20

    I really enjoy your site., very technical and useful info . Thanks for your effort. I am curious to know your thoughts on the following. I have been toying with the idea of waiting to trim brass until after 1x firing so that the case is more uniform before I cut off neck meat. I can’t determine if new brass is long or short due to neck length or variations other parts in new brass. I’ve tried sizing new brass first, but my current brass is so small that it is not squeezed by the die.

    • SamMillard
      March 5, 2016 at 20:50

      I’ve done it both ways, but now I trim cases every time I load. I agree that there’s no way to really know where the length variation comes from on new brass, but so far it hasn’t hurt to trim them. As far as sizing, I don’t think I’ve ever had a FL or body die do any work on the body portion of a new case. The reason I run them through the die is to clean up the neck and set the O.D. of the neck for the tension I want.

      • Casey
        March 10, 2016 at 21:34

        Sam, thanks for the reply. I will be anxiously awaiting the next part to your story as I am tracing your steps for a 7 rem mag.

  • Kyle
    March 17, 2016 at 17:00

    What is the procedure you use to measure the web diameter on your cases?? Do you have a video?

    • SamMillard
      March 17, 2016 at 17:13

      I just measure the web below the rim or belt when the brass is new, then measure for the fattest diameter in the same spot after firing. Then I measure it after sizing. I use the same digital calipers I use for everything else. I’m not sure if I’ve shown that in a video, but I’ll put it on the list for the next reloading video. Thanks!

  • James Bergman
    August 19, 2016 at 13:50

    I don’t like weighing the casings either. It is tedious, and I don’t know how much of a difference it makes. However, it is good for finding those bad casings. Also, I have heard a little bit about annealing the casings to make them last longer. However, you don’t spend much time on it, you only mention annealing once. Do you have any tips on this?

  • Jeremiah Johnson
    October 8, 2016 at 16:40

    Great info, Sam! Finally started loading ammo 2 weeks ago and so far it’s really paying off. Your videos and articles have really helped me understand the methods and reasons behind it. Thanks again

  • Daniel
    October 30, 2018 at 09:30

    Hi “Sam” I want to try the new reloading bullet Hornady ELDX I have a Sako 6.5×55 with a 1 to 8 twist can you recommen a good grain of bullet for my rifle thank you Sincerely Daniel

    • SamMillard
      October 30, 2018 at 09:33

      The 143-grain ELD-X would be the one.

  • Cameron Kuykendall
    January 29, 2019 at 13:46

    I am trying to determine which bushing to purchase. If it’s the first time with the new brass and new caliber, how do I determine the correct bushing, if I haven’t loaded a full round yet to measure? Hopefully that question makes sense.

  • Justin Kolander
    July 14, 2020 at 07:18

    Love your webpage and YouTube videos! Have a couple questions about expanding necks with the Sinclair mandrel/dies. Are you using Sinclair’s “expander” mandrel or “turning” mandrel – basically .001 vs .002 tension? Also, any advice on the carbide vs stainless steel mandrels?

    • Sam
      Sam Millard
      July 15, 2020 at 06:39

      I use the SS expander mandrel. It’s ground .001″ under bullet diameter.

  • Tim Dey
    April 29, 2021 at 17:37

    Sam, found this article after sending a question recently about annealing new brass. just like you said before “you probably already covered it”. Thanks.
    Good Stuff!


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