Peterson Brass 300 Winchester Mag Unprimed Box of 50

Peterson Brass 300 Winchester Mag Unprimed Box of 50
Item #:PCC300WM
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Availability:In Stock
Due to the packaging and shipping process, case necks are often slightly dinged or bent and need to be rounded up and sized to give proper neck tension. New and/or fired cases must be full-length resized or have the expander ball of the sizing die run through the case neck prior to loading.
Read 23 Reviews

Product Information

300 Winchester Magnum

All 50 count listings of Peterson Cartridge casings come in one of their plastic ammo boxes.

Made in the U.S.A.


Peterson makes the traditional SAAMI spec’d version that headspaces off the belt. But it also makes a version that headspaces off the shoulder. Peterson calls that version the .300 Win Mag- Long. This listing is the SAAMI spec version.

“I am extremely pleased to announce that as of July 20th, 2020, Peterson Cartridge has now added .300 Winchester Magnum brass to its’ product line,” stated president, Derek Peterson. “The road for us to produce this belted magnum case has been long, frustrating, and expensive. It has taken us over three years to release this cartridge and cost us well over $50,000 in experimental tooling alone.”

Peterson continued, “Producing a brass casing with a really good belt is a difficult thing. Getting the tooling just right is an iterative process, and these .300 Win Mags took more iterations than I care to remember.

“To make a new caliber casing for the first time, we design and order all the tooling. After it arrives, we do what we call a proof-of-concept (p-o-c) run. With most of the 30+ new tool packs we’ve designed, we end up with a “Best Vision” casing after one or two iterations.

“But these .300 Win Mags! With many of the p-o-c runs, the resultant belt wasn’t crisp enough. So we would redesign and order different tooling and try again. With some runs we’d get a good belt, but it wasn’t in the exact correct location. Some runs, the belt was good and in the correct location, but the equipment wouldn’t run it efficiently or the scrap rate was too high. It took a few different tooling iterations to get the grain structure in the casing walls just right. After some of the failed iterations we would speculate, maybe the problem is with the dimensions of the brass cups we are using as raw material. So, we’d redesign those, and try again.

“But after three years of unsettling self-doubt, and countless iterations WE GOT THE BELT. We can now make belted magnum casings! And we have really good .300 Win Mag casings on the shelf, with as good a belt as any in the industry. Our ballistician has shot some of these 20 times in a row, at SAAMI max pressure, with a minimum shoulder resize and they are still holding up well.”

Peterson concluded, “If you are one of the many customers who’ve called us every week to say, “When are you people ever going to release .300 Win Mag,” we have two responses. First, thank you for waiting. Second, FINALLY, here you go; we got the belt!”

Warning: Only use Peterson Cartridge Co. casings in firearms in good condition, designed, marked, and chambered for this cartridge. Do not use Peterson Cartridge Co casings for “fire forming” or any other purpose other than what they were designed and tested for. Peterson retains no responsibility for the enclosed casings if they are used outside of the manufacturer’s recommendations.

This is not loaded ammunition.

Read 23 Reviews - Average Rating: 5 stars

Peterson 300 WM Brass

By Brian B. on Feb 02, 2024
Great prodoct. Came nicely packaged in cartridge boxes which I will use to store my loaded ammo. Also great service because Graf & Sons got it here quickly!

Peterson .300 WM Brass

By Ray R. on Nov 22, 2023
“Excellent quality brass” after receiving my first purchase of .300 WM brass I was sold instantly! The quality of brass is top notch and the reason I’ve already purchased again. I live in Alaska and my order was processed and delivered in a short period. Can’t say enough about the service and quality of Peterson brass!

Peterson 300 win mag brass

By James G. on Nov 17, 2023
Brass comes in a very nice box so no dents or dings when it arrived. Brass looks extremely uniform and well made. I have not gotten a chance to load it yet but so far very impressed.


By Brian L. on Oct 02, 2023
The shoulders all measure the same, to the thousands. That's great and they are all a good length. 300WM new brass can be shorter in shoulder length. These compare to Lapua in length. They are 13 thousands from my min SAAMI spec chamber. 1 of 7 cases were 2 thousands shorter in length. But all were proper length.
There is so much shoulder movement in 300WM that when I am finished with a load, I want to start with a fresh set of brass and NOW keep all the fired and anneal counts, all fired with the same exact load. So I can watch the shoulder movement and set back issues. These 50 cases will be perfect.

300 Win mag brass

By Daniel B. on Sep 29, 2023
Came with a nice case all in spec and looks great

Peterson 300 W M brass

By Daniel A. on Aug 29, 2023
Very good brass I would buy it again, uniform, tight primer pockets. Didn’t have to do anything to it just loaded them up and when to the range. Oops one piece of brass out of 100 didn’t have a flash hole 😬so I drill it 👍

Peterson 300 win mag brass

By Braxton H. on Jun 16, 2023
Very pleased with the quality and consistency of this brass. New brass not even fire formed yet shot .5 moa at 700yds. Cannot complaint one bit about this product!

Quality Brass

By George G. on Mar 27, 2023
My first time purchasing Peterson brass, and after careful examination it appears to be of excellent quality. I have not loaded this brass yet, but am looking forward to it. The price point was spot on, particularly since it is nearly impossible to find 300 WM brass at this time. The only other offerings I could find were Lapua and Nosler brass, and they were far more expensive than Peterson.

Peterson 300 Win Mag Brass

By Darreyl S. on Mar 27, 2023
Bought some of this brass in February and was presently surprised the brass came packaged in its own plastic ammo box. All parts measured within 0.003 mils of being the same length. Finally, was able to shoot some of my loads over the weekend and they shot very well. Looking forward to round two of reloading some of this brass.

I would recommend using this brass and will buy more of it!

Peterson brass

By Tarin F. on Mar 02, 2023
Amazing quality! Started with 280 ai brass because I couldn't find any other brass for it glad I did! So I bought more in different calibers and same fine quality! Definitely will be using this brass for awhile!

Fantastic brass

By Andrew H. on Feb 18, 2023
Very high quality brass which is packaged nice so there are no ding/dents. At least as good as Lapua brass at a much better price.


By Larry M. on Feb 13, 2023
My first time at trying Peterson Brass!! Packaging was excellent! The overall length of the cases are very close in length to each other and i neck sized them and only had to do a small amount of trimming to get them in spec.

Peterson 300 WM brass

By Jim W. on Feb 06, 2023
Very consistent weight wise. Came in very good condition. I did quickly resize the neck as the diameter was 0.330, and I wanted a little less neck tension on my initial loaded rounds.

Peterson brass

By Lanny H. on Jan 30, 2023
Great brass.

Fantastic brass for Win Mag

By Brian M. on Jan 30, 2023
This brass is every bit as good as ADG.
Comes well packaged and in good condition ready for the mandrel, and initial loading. Reduce your load if you currently use thinner brass.

Peterson 300 win mag. Brass

By Chris H. on Jan 26, 2023
Liked the 6x47 brass so much bought some 300 win mag and wasn’t disappointed. This brass is very consistent in ever aspect haven’t had any issues with it. Will be buying more.

Peterson 300 WM brass

By Mark O. on Jan 24, 2023
Brass is fantastic. No dents, mouths are perfectly round. I’ve bought several of this brass over the past year. I will continue to buy it. Some of the best I’ve bought.

Excellent Brass

By Ben P. on Jan 24, 2023
I bought and loaded this for a friend. While I can’t speak to firing it, when measured I was very happy with the uniformity of this brass; especially for the large size of 300WM. The cartridges looked like jewelry and I am confident that they will perform as well as they look. Peterson brass is my go to.

Amazing brass

By Daniel O. on Mar 31, 2022
Great quality, comes in nice ammo box. On my 6th reload with it and still holding up great. Highly recommended

Excellent brass

By Mark M. on Nov 16, 2020
Weight was very consistent. No culls in the whole batch. Come in a good cartridge box. Friends have reported being able to reload other calibers 7 or 8 times with no primer pocket problems. Time will tell on the 300 WM to see if I need to resize in front of the belt, but looking good so far. I now consider Peterson brass a good long term investment for my shooting. Highly recommended.

Great brass

By Brett L. on Oct 09, 2020
Trim length and weight are very consistent. Shoots very well.

Peterson 300 wm brass

By Jeff Y. on Oct 08, 2020
Brass arrived superbly packaged by Grafs, the 2 ammo boxes were inside three boxes with packing like nesting dolls. I have since began measuring the brass as I have never used it before. It is only 0.008" shorter than fire formed shoulder bumped(-0.002" )brass fitted to my 300 win mag chamber . This will make fire forming a breeze. Neck wall thickness is within 0,0145" to 0.0150" that is a closer tolerance than any factory brass I have ever bought.

Peterson 300 win mag brass

By Jason C. on Oct 06, 2020
Brass comes in a very nice box so no dents or dings when it arrived. Brass looks extremely uniform and well made. Definitely thicker than Federal or Winchester brass that I have used.
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