Peterson Brass 300 Winchester Mag Long Unprimed Bulk Box of 250

Peterson Brass 300 Winchester Mag Long Unprimed Bulk Box of 250
Item #:PCC300WML250
$1.55 per piece
Shipping: One flat fee of $12.95 per online order.
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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 2 Reviews

Product Information

This is a Bulk package of Peterson Cartridge casings, they will not 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 2 Reviews - Average Rating: 5 stars

So far looks good

By Paul G. on Oct 20, 2020
I’ve only fired this brass one round while testing the Berger bullets. So far looks good no brass thinning near base where I have had head separation from other brass

Peterson 300WM Long Brass

By Craig L. on Oct 19, 2020
The annealing looks darn good and appears to be consistent depth on the case. I weighed 10 random cases and the SD was 0.433 gr across the 10 cases. The average weight of the Peterson brass was exactly 11.0 gr heavier than the average weight of Remington brass I have on hand. A new Remington brass was 0.014 shorter than the fired brass and 0.011 shorter than the new Peterson Long brass.
The fired brass is ONLY 0.002 longer than the new brass measurement so the Long concept appears to be exactly what they stated and definitely should lengthen brass life. This was also a stout load of xx.x gr of RL26 so it was good test for stretch. Will post up further info once I resize and re-prime for primer pocket integrity. The brass measurements are exactly as advertised so the brass life HAS to be better going forward.
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