Peterson Brass 300 Winchester Mag Long Unprimed Box of 50

Peterson Brass 300 Winchester Mag Long Unprimed Box of 50
Item #:PCC300WML50
$1.70 per piece
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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 27 Reviews

Product Information

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

Made in the U.S.A.

Peterson Cartridge Co. of Pittsburgh, PA announced it is producing .300 Win Mag casings in two versions. 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 this version the .300 Win Mag Long.

Shooters that reload .300 Win Mag casings have often wished they could get more reloads from their casings. Well now you can!

Derek Peterson, president of Peterson Cartridge explains, “Traditional .300 Win Mag casings tend to show signs of case head separation after only 5 to 7 firings.

“Here’s why. The SAAMI specs for any caliber, list a minimum and a maximum tolerance for each dimension on the casing and the rifle’s chamber. With most calibers, the max dimension of the casing, for length-to-shoulder (L-T-S), has the shoulder of the casing right up against the chamber wall. With .300 Win Mag, unlike most other calibers, if your rifle’s chamber is cut to the SAAMI minimum for L-T-S, and your casing is at the max length-to-shoulder dimension, the casing shoulder is still .0095” away from the chamber wall. With the same minimum rifle chamber, a casing at nominal L-T-S is .012” away from the chamber wall. In a worst-case scenario, if the casing was produced at the SAAMI minimum L-T-S, and the chamber was cut at the maximum L-T-S dimension, the casing shoulder could be up to .026” away from the chamber wall. That might not sound like a lot, but it is.

“That large gap is what causes the casing to stretch so much when it is fired. It’s that stretching that causes premature case head separation.”

Peterson continued, “With Peterson .300 Win Mag- Long casings, we make them with a longer L-T-S dimension. All the other dimensions are SAAMI spec. But the longer L-T-S prevents the casing from stretching excessively on the 1st firing. The casing has more support, which translates to less stretching, which translates to longer case life.”

Peterson concluded, “If you are a handloader, that wants more reloads from your .300 Win Mag casings, we think you will appreciate our new .300 Win Mag - Long casings. I’d like it if you’d give them a try and let us know what you think.”


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 27 Reviews - Average Rating: 4.7 stars

Peterson 300 win mag long

By Ed I. on Mar 18, 2024
Like many others I ran all cases through my neck sizing die and mandrel. Chamfered necks to my liking and loaded an OCW test with 185 Berger classic hunter bullets in front of H4831SC and Remington 9 1//2s. All ten loads were MOA. The best being a ragged four shot 3/8 hole. I call that good enough for a totally new load combination. Ordered another box just to make sure to have some in back up. Time will tell for how many firings I get but it looks promising.

Exceptional Brass

By Ronald L. on Feb 28, 2024
Upon receiving my order of 50 pieces of Peterson 300 Win Mag-Long brass I began taking measurements. I did not measure with water, but in every other aspect- length, neck ID and OD, shoulder, ovality, neck runout-it was perfect. I reload for 13 calibers, and Peterson is always either 1 or 2. Highly recommend this brass!!

Top Brass

By DAVID G. on Feb 20, 2024
Very impressive.

300wm long brass

By Greg F. on Feb 12, 2024
Before using this brass , I could only reload 4 or 5 times before of case separation. With Peterson brass I'm up to 8 reloads with no sign of separation . !!! Good stuff


By Jack R. on Feb 08, 2024
the latest batch of Peterson brass has been consistent, clean, sized and annealed. After a little prep, loading and range day, brass showed no wear, heavy flow or primer pocket bulge. The new long cartridge series add a little ease in bullet seating and improved group sizes. Cant be more satisfied Jackmann

300 Winchester Long Peterson Brass

By David S. on Feb 01, 2024
I have not had a chance to use this brass yet. When received brass was in good condition. I gave a friend 10 hulls to load and shoot. He was pleased with the results and also made an order for 250. I want to recommend
Graf and Sons for the ease of doing business as this was my first order. Nice company to do business with.

Peterson 300 win mag brass

By James K. on Jan 30, 2024
Love it, great brass, couldn't be happier

300 wm long brass

By Patrick M. on Dec 29, 2023
I love the idea. I think it's very innovative and the box that the brass comes in was very nice. I didn't reduce the stars for this. But 5 of the pieces of brass had dented necks like somebody in the factory is just throwing them around. Or dumping them into a bin of some kind and they are being injured. It seems like I should be able to load them when they're brand new and not resize them to fix the damage. I'm sure you've heard this from some other people and are working to fix it. Thanks

300 win long

By Andy B. on Nov 30, 2023
Great idea but a waste of money, not consistent and had dented brass

300 WM Long brass

By Pat W. on Nov 12, 2023
Brass arrived in great condition, and upon measuring 10% of them they all were within .001 of each other. Loaded up the first 5 to test at the range and they shot a group that was sub MOA at 100 yards. I am very impressed with the brass, and will be ordering more. Primer pockets were uniform and brass held up well after firing.

300 Winchester magnum long

By Cass L. on Nov 09, 2023
I traditionally have used Nosler or Lapua brass but after receiving my Peterson brass, I’m impressed. When my brass came in I visually inspected to only find one piece of brass with a minor dent in the neck. The other cases were in great condition. But this was nothing that would affect performance and a quick run through a neck sizer and it was gone. So far they are holding up and seem to be the same or better quality as higher priced manufacturers. Just waiting to see how they hold up on the long haul.

300 winchester long

By Jay H. on Oct 22, 2023
Great packaging and shipping. Loaded a proven load straight out of the box with 1/2 MOA results.

Waste of money

By Lonnie C. on Oct 20, 2023
I recently made a first time purchase of 50 pieces of this brass, and it was the worst looking brass i have ever come across. The necks were dinged up and had flat spots on them, and more than half of the cases were dented. I purchased this brass because it was rumored be top notch, and to save time on components and fire forming, but all I did was waste time and money. I contacted Peterson cartridge company and they offered to send a return shipping label, so I could send it back to be inspected again. This brass came from the factory that way, so I wasn't going to waste my time and money returning it. I threw it in the trash, and ended up with nothing more than a one hundred dollar plastic ammo box So much for the rumor about their brass being top notch.

300 WIN MAG - Peterson Long Brass

By David W. on Sep 21, 2023
Tested 9/21/2023
300WM 26" barrel (M40) 1x10 twist
N568 powder xx.x grain
185 grain Lapua Scenar / 3.35 COAL
215M primer
Achieved 2760 FPS
Same FPS results with grain load used with Lapua brass.
Good grouping at 200 yds.
Very happy with Peterson brass - 1st time use

About Time

By Tyler T. on Sep 12, 2023
Finally got some of this brass and it is beautiful. Arrived really well packed with only a few nicks dinged up out of 100pcs. Still gonna hit em all and get out to the range asap.

Peterson 300 win mag long brass

By Frank N. on Jul 02, 2023
I compared my first box of long brass to my fired brass, .002" shorter perfect, avoid the stretching of new unfired brass. I'm expecting longer brass life from the Peterson long brass!! And it came packaged in it's own 50 round case. Very Nice!

Top notch brass

By Douglas W. on Jun 16, 2023
I have been using this brass for a year now and it is the best, hard to find in stock!


By Paul H. on May 16, 2023
The best brass I’ve ever bought I was so surprised how close to fired brass they measured they were exactly what I bump my brass back to. Certainly going to prolong the life considerably. Certainly worth the money

300 WinMag Long

By Jim S. on Apr 25, 2023
I purchased 100 of these cases. They arrived in almost perfect condition, with only a few of the case mouths slightly out of round -- easily fixed with a neck size mandrel. The first thing I did was to chamber a few of the unfired cases in my rifle, to make sure they were not "too long." No problems chambering them. Then I weighed the water volume of 5 of the cases, expecting to be pleased if they were within one grain of each other. Imagine my pleasure when I found them to be all within ONE TENTH of a grain! I have shot only 15 of these cases, trying out 3 new powder charges at 100 yards. All of the loads performed superbly, with one 5-shot group all going into the same 30 caliber hole, appearing to be only one shot. Holy cow! I really like this brass! The "long" version of the 300 Win Mag makes a lot of sense. I visually compared the unfired "long" Peterson brass to some unfired other major brand brass. The extra length is very obvious, appearing to be almost a 16th of an inch. This extra length avoids that huge stretch upon the first firing. Kudos to Peterson -- I expect all of these cases to perform as well as the first 15!

Peterson 300 WM Long

By Dale O. on Apr 25, 2023
I bought this brass avoids the excessive case prep of the brass I had been using previously. With the extra shoulder length I only have about 0.003” stretch on first firing. I only gave 4 stars because the mouths are very rough in as received state. All brass was uniform for dimensions and dead on if not it was very close to Peterson stated QC label in their website for the lot number shipped. I ended up buying 250 total of these cases which should wear this barrel out before I retire them.

Best Brass Ever!

By Benjamin T. on Mar 24, 2022
This brass is the best brass I have ever used for my 300wm. Great job Peterson Brass! You have a new lifelong customer.

Just another 5 star review

By John M. on Aug 16, 2021
Can't add anything to the reviews above except this is the best packaging I've seen for brass and I've bought from all the big name manufacturers. Another happy customer.

300WM Long. Amazing Results

By Jason B. on Jun 10, 2021
300 WM Long brass by Peterson is showing amazing results. I found the new brass to only be .003 off instead of the average .021 thou I was finding with other high end brass. And as much as .026 thou with cheaper brass. I am getting more firings, more precise results on target, lower SD and ES. I will be buying these from now on and highly recommend them.

What a Phenomenal Idea!

By Joe L. on Dec 06, 2020
I’ve been using 300 WM brass to make (or form) 7mmRM brass that actually fit the chamber on the first firing. Very happy to get proper brass from the get go for my 300. Haven’t used the Peterson brass in 300 yet but have used it in other calibers with excellent results.

Peterson Brass - why not buy the best

By Jerry N. on Nov 11, 2020
Peterson Brass is the best brass I have ever used. The consistency is outstanding and the brass is beautifully prepared to be loaded. I just run a mandrel through the neck to make sure nothing got dinged in transit and it is ready to load. Nothing has ever gotten dinged it transit because it is superbly packaged. The Long option is the way to go - you don't have to fire form this brass to start getting great results. Not stretching the case to fit your rifles headspace has to make the brass last longer.

The brass is slightly thicker so the case capacity is a little less so back your loads down half a grain or so.

Be prepared to be pleased with Peterson's Brass - my only complaint is that they, as of yet, don't make cases for every cartridge and supply is sometimes tight.

300 winchester long peterson brass

By Vincent M. on Nov 10, 2020
Wow a company that makes the long brass to fit the chamber and avoid fire forming. As usual top quality in weight, length, and every other thing that you would ask for in a top quality products. packaging in above any standard that would cause the product to be damaged in shipping. And cost yes a somewhat higher but you are getting for once a quality product as advertised and with proper care will outlast many other so called quality products as advertised


By Lance K. on Oct 12, 2020
A company that produces virgin brass that is not .014-.020" shorter than your cut chamber!
Very consistent in weight, OAL, headspace, and high quality fully prepped brass. I just ran it through my neck sizer and expander mandrel to ensure proper neck tension, and ready to load. No fire forming needed.
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