High-Velocity 7mm Rem Mag Loads with IMR Enduron Powders

7mm Rem Mag is a VERY popular hunting cartridge, and for good reasons! With this cartridge you get more velocity compared to 300 Win Mag, and less recoil as well. With enough power to stop almost any game animal in North America, it’s hard to go wrong with this powerful “platform”. In this article, we’ll build on the previous story by looking at two popular IMR Enduron powders for this cartridge.

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Introduction: New Powders for an old Favorite 


Above: Lyman gear used to load 7mm Rem Mag with IMR Powders

I could no longer get my old favorite powder for the 7mm Remington Magnum. Gavin recommended that I try some of the new Enduron powders, IMR 8133 and IMR 4955

The Enduron powders are supposed to reduce barrel fouling and be less temperature sensitive while still providing the desired velocity. I researched the Enduron powders by reading Hodgdon’s manual, and learned that John Barsness had authored a chapter “New Powders and Bullets in the 7mm Remington Magnum” in his recent book The Big Book of Gun Gack III. He reported good results from IMR 8133. PLUS, I could find the Enduron powders on the shelf at my local gun shop! 

Building on Our Last Story

You’ll want to check out our first story in this two-part series covering loading 7mm Rem Mag with Budget Lyman reloading equipment!

Here’s the video from that story:

Now, on to loading and shooting!

About IMR Enduron Powders

IMR-powders-sxs-with-powder-samples

The IMR Enduron Powders were introduced several years ago and provide an alternative to others, with some interesting advantages. They contain a copper fouling reduction additive, which significantly reduces barrel fouling. Reduced barrel fouling could be a big advantage in high use rifles, such as varmint rifles and match rifles. 

They also are formulated to be temperature insensitive, similar to what we’ve seen with Hodgdon’s Extreme series of powders. Remaining stable in vastly different temperatures is a huge advantage for many of us who may work up a load during the heat of summer, then hunt in much cooler temperatures of fall and winter. 

The Enduron powders are said to provide optimal load density, leading to low SD numbers for pressure and velocity, which should in turn, provide good accuracy. My work with the 7mm Remington Magnum revealed good accuracy, on par with what I’ve seen from other loads with this rifle, grouping roughly an inch at 100 yards. They’re supposed to be environmentally friendly as well. 

The Enduron lineup has broadened since their introduction and there is likely an IMR Enduron powder made which can replace older powders. I found that IMR 8133 in particular is a fine replacement for a slow burning powder which I can no longer find. I was very impressed with the velocity obtained, as well as the rather low SD & ES numbers. 

IMR Enduron 4955 is a versatile, match-grade propellant with a mid-range burn speed that is in between IMR4451 and IMR7977. It is an extruded powder and provides top performance for big game cartridges like 25-06, 270 Winchester, 280 Remington and 300 Win Mag, among other cartridges. The main features of the Enduron series are copper fouling eliminator, insensitivity to temperature changes, ideal loading density and being environmentally friendly.

This propellant performs comparably to Hodgdon H4831 but charge weights are materially different.

IMR recommends always consulting www.IMRReloading.com for the most accurate, up-to-date data.

IMR Enduron 8133 is the slowest burn rate in the Enduron family. Loading density is perfect for magnums, contributing to superb uniformity. This is a true magnum propellant yielding outstanding performance in 6.5-300 Weatherby, 264 Win Mag, 28 Nosler and 300 Rem Ultra Mag, among other cartridges. Loading density is perfect for magnums, nicely filling the case at maximum charges, contributing to superb uniformity and accuracy.

The main features of the Enduron series are copper fouling eliminator, insensitivity to temperature changes, ideal loading density and being environmentally friendly.

IMR 8133 performs comparably to Hodgdon Retumbo but charge weights are materially different.

IMR recommends always consulting www.IMRReloading.com for the most accurate, up-to-date data.

Choosing other Components for the 7mm Remington Magnum

When selecting loading components for a high velocity magnum cartridge, think of slower burning powders, magnum primers, sleek high-BC bullets. The 7mm Remington Magnum is well suited for longish range hunting of most North American game, including elk. The cartridge produces enough velocity to over stress some bullets if they contact big game at modest ranges. This can lead to over expansion and under penetration, an undesirable situation! If such shots are anticipated, or if the game is particularly large and tough such as bull elk, then a sturdy bullet should be selected. My plans for this rifle, this year, include only mule deer, possibly out to 300 or 400 yards. The 150 grain Hornady ELD-X should perform well on deer. 

About the Hornady 150 grain 7mm ELD-X bullet

From the Hornady Product Page:

The ELD-X® (Extremely Low Drag – eXpanding) bullet is a technologically advanced, match accurate, ALL-RANGE hunting bullet featuring highest-in-class ballistic coefficients and consistent, controlled expansion at ALL practical hunting distances.

The Enduron powders tested, IMR 4955 and IMR 8133 produced excellent velocity and the accuracy is good too. We tested the loads at about 80 degrees. Later in the hunting season, I’m anticipating considerably cooler temps, and hopefully I can use the rifle this winter for coyotes as well. Then I’ll have a better feel for how the powders perform in very different temperatures.

While loading a maximum charge of 77 grains IMR 8133, it nearly filled the Winchester case and resulted in a compressed load. With both powders tested, I noted that the SD and ES both shrank as powder charges increased. 

With the fairly large amount of slow burning powder to ignite, a magnum primer makes sense. I’m using the Federal 215 large rifle, magnum, match primer. At least in theory, the match primer should produce more consistent ignition and smaller variations in velocity. 

Chronograph Results

 

You can see here that IMR 8133 produced better velocity, better SD, and better ES. If you had to pick a load, the IMR 8133 would be it! On the other hand, IMR 4955 could prove to perform well with additional load development.

Special Considerations with Belted Cases: 

Factory belted magnum cases are made to headspace on the belt, however this can lead to excessive case stretching and even case-head separation! Case life can be extended by setting the sizing die so that the case headspaces on the shoulder instead. L.E. Wilson makes an Adjustable Case Gauge that can be set to match the shoulder of cases fired in your rifle. 

Conclusion

The Enduron powders, IMR 4955 and IMR 8133 are well suited for the 7mm Remington Magnum producing good velocity. The 150 grain Hornady ELD-X bullet loaded to nearly 3,300 fps and zeroed at 200 yards drops only about 5” at 300 yards making it a great choice for hunting deer and similar sized animals in open country. 


Above: My 2020 Wyoming buck and the 7mm Remington Magnum Ruger Number One.

Wish me luck during my hunting adventures this Fall!

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Thanks,
Guy Miner

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