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IMR enduron powder

.303 British
New Powders - New Loads

by Tim Banse

Reloading the .303 British with IMR's new 4166 and 4451 Enduron powders.

IMR enduron powder

In 2015 IMR introduced three new Enduron powders, more particularly, IMR 4166, IMR 4451, and IMR 7977. All three of these new propellants feature small kernels for easy metering and a built-in copper fouling eliminator. Morever, Enduron powders are not sensitive to temperature changes. But here lies the real eyebrow raiser: according to Hodgdon, its IMR 4166 is nothing less than a "versatile, match grade propellant".

With that preface in mind we present load data for two of the three powders in a variety of bullet weights and loads. And we've fused into that load table some information on the ubiquitous .303 Mark 7 military load as well as factory Remington 174 and 180 grain weights, which lends perspective on relative velocity. Also for perspective's sake, we've included load data for IMR 3031. That's for the simple reason that venerable Improved Military Rifle 3031 was the first propellant after Cordite to be loaded in the .303 British.

Powder Bullet Weight Bullet Diameter COL Primer Charge (grains) Velocity (fps) Pressure Charge (grains) Velocity
(fps)
Pressure CUP
IMR 4166 125 .311 2.915 Remington Large Rifle 44.2 2,739 37,500 47.2 2,907 43,000
IMR 4166 150 .312 2.995 Remington Large Rifle 39.9 2,477 36,400 43.9 2,693 43,600
IMR 3031 150 .312 2.995 41 2,632 46,100 PSI
Remington Factory FMJ 174 .311 3.075 2,475
IMR 4166 174 .311 3.075 Remington Large Rifle 2,475
IMR 4451 174 .311 3.075 Remington Large Rifle 45.6 2,397 36,800 49.6C 2,590 43,300
Military Mark VII load 174 FMJ .311 3.075 2,440 45,000 CUP
(SAAMI Max)
Remington Factory Core Lokt 180 .311 3.075 2,460
IMR 3031 180 .311 3.075 38.3 2,341 46,500 PSI
IMR 4166 Speer 180 Hot-Core .311 3.075 Remington Large Rifle 37.5 2,265 34,900 40.8 2,453 42,300
IMR 4451 Speer 180 Hot-Core .311 3.075 Remington Large Rifle 45.2 2,361 37,300 49.2C 2,556 43,900