TESTED: IMR 8133 Smokeless Powder

Last year I was unable to find my old favorite slow burning powders locally, but I found a couple of pounds of IMR 8133 and decided to investigate. Since then, I’ve become a fan of this powder, which we’ll take a close look at in this story!


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About IMR 8133

I’d never used IMR 8133  before but knew that it was a slow burning powder with some applicability for a couple of my personal hunting rifles: a 7mm Remington Magnum and a 25-06. It is the slowest-burning of the Enduron line and combines the copper fouling reduction and temperature insensitivity properties of Hodgdon powders. 

From the manufacturer’s product page:

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.

Available in 1-LB and 8-LB containers.

I found the attributes of this newer powder quite attractive — high velocity potential, reduced copper jacket fouling in the bore, and temperature insensitivity. 

Burn Rate Analysis

IMR 8133 falls into the magnum powder range. The burn rate chart shows it slightly slower than Hodgdon Retumbo. We took a closer look at this powder here

IMR 8133 Cartridges and Loads

Below are a few cartridges and loads using IMR 8133. I personally tested 25-06 and 7mm magnum. If you use these loads, please work up carefully as these are max-level  loads and consult multiple OEM sources just to be sure.

The first cartridge I loaded with IMR 8133 was a 7mm Remington Magnum — a Ruger No.1 single shot rifle with a 26” barrel. Testing the 7mm Remington Magnum, I was thoroughly impressed with the velocity achieved with Hornady’s 150 grain ELD-X hunting bullet.

Guy shooting the 7mm Rem ag at the UR Ridgeline.

From the 26” barreled Ruger, we saw an average of 3,282 fps, which should prove to be an excellent open-country hunting load for deer and antelope-sized game. Zeroed at 300 yards, this bullet drops only 7.9” at 400 yards!

For hunters, this is a true “hold on hair” setup at 400 yards and somewhat beyond. 

We also took a look at IMR 8133 in a recent article about loading for the 25-06 cartridge.

With the 25-06, I used IMR 8133 with two different 115 grain hunting bullets: the Berger VLD and Nosler’s Ballistic Tip. Velocity and accuracy were both good. This rifle, my 700 CDL, usually produces groups around ¾” or less. I achieved that same standard with both loads.

Muzzle velocity was quite impressive. The  Berger averaged 3145 fps and the Nosler averaged 3199 fps! Loads with these numbers are flat shooting, traveling longer distances before dropping significantly. For example, the bullet drops only 9.3” at 400 yards with the 115 grain Berger VLD zeroed at 300 yards, making shots to 400 yards or a bit further easy for a skilled rifleman.

Under the Microscope

We took a closer look at IMR 8133 and similar powders under the microscope.

IMR 8133 grains had a larger length and diameter than Magnum, Varget, and Retumbo.

In the picture at right above, you see from left to right: Ramshot Magnum, Hodgdon Varget, Hodgdon Retumbo, and  IMR 8133.



IMR 8133 is an Enduron powder, making it less temperature sensitive. It is also formulated to reduce copper fouling in the rifle’s bore. Many hunters shoot copper bullets such as Barnes in overbore/magnum cartridges. This powder might be beneficial for them.  IMR 8133 is especially well-suited for use in overbore cartridges. I noted that as the charge weights approached maximum level loads, the SD and ES figures both diminished, providing excellent consistency. 


Like a few similar powders, IMR 8133 is best used in overbore or magnum type cartridges where its slow-burning properties shine. There are better choices for milder cartridges such as the 6.5 Creedmoor and the 308 Winchester. 

IMR 8133 performed well in both of the cartridges we tested — the 7mm Remington Magnum and the 25-06. It can be expected to perform well in similar rifle cartridges. IMR 8133 is ideal for anyone who relies on overbore cartridges, including long-range target shooters and hunters.  It provided excellent velocity, small SD and ES spreads, and good accuracy in our tests. I’ll be using IMR 8133 in my 7mm Remington Magnum hunting rifle and I won’t be surprised if Gavin and I try it in the 257 Weatherby Magnum either. 

Get IMR 8133

Find IMR 8133 at Midsouth Shooters Supply or directly from Hodgdon. Midsouth Shooters supply shows the 8 lb jug priced at $283.11 and a single pound of IMR 8133 at $40.37 as of April 2022.

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Guy Miner 


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