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The Ultimate Reloading Manual
Wolfe Publishing Group
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The Ultimate Reloading Manual
load development

Top 10 Reloaded Rifle Cartridges #6: .300 Winchester Magnum

Author: Brian Pearce
Date: Sep 20 2021

A Ruger M77 MKII topped with a Redfield Revolution 4-12x scope was used to develop handload data.
©2018 Matthew
West photo

In 1956 Winchester announced the .458 Winchester Magnum followed by the .264 and .338 Winchester Magnums in 1958. Each was based on the belted .300/.375 H&H Magnum case, but it was blown out and shortened, resulting in an overall cartridge length of 3.340 inches, the same as the .30-06. These were the original “short magnum” cartridges, as the H&H rounds required a longer action to house their 3.600-inch overall lengths.

There were rumors that a new .30-caliber magnum would soon follow, and most people speculated that the .264/.338 Winchester case dimensions, including shoulder position, would be used but necked to accept .308-inch bullets. In anticipation, the wildcat .30-338 cartridge was soon developed, which became popular among hunters and long-range competitors. Around 1960 Norma introduced the .308 Norma Magnum that shared similar dimensions.

It wasn’t until 1963, however, that Winchester finally announced the .300 Winchester Magnum in the pre-’64 Model 70 Alaskan rifle. It was based on the same belted case, but the shoulder position was moved forward to increase powder capacity and velocity, which resulted in a shorter neck. Original factory load ballistics advertised a 150-grain bullet at 3,400 fps, a 180 grain at 3,070 fps and a 220 grain at 2,720 fps. It became an overnight success, and in spite of many competing .30-caliber magnum cartridges, both old and new, the .300 Winchester Magnum is perhaps the most popular .30-caliber magnum cartridge in history.

The vast majority of .300 Winchesters are sold to hunters, with virtually every major manufacturer offering rifles. The cartridge offers versatility that allows it to easily take game in open country, where long shots are common, but it’s also suitable for game such as elk, moose and even the great bears of the North – with premium hunting bullets. It is popular with Africa-bound hunters in pursuit of plains game. It has found favor with long-range target shooters, law enforcement and even our military, where it is used for sniping and long-range target work.

Reference factory loads from Black Hills,
Federal, Hornady and Remington were checked
for velocity.

With nearly four decades of personal experience with the .300 Winchester Magnum, I can conclude that it is a great hunting and field cartridge. It has accounted for many head of big game, including pronghorn at long distances, mule deer in sagebrush country, elk in the rugged mountains of the Continental Divide and several black bears that were anchored with authority. It has also taken many coyotes that stopped to look back at distances they thought were completely safe. When kept within normal limits and stoked with correct bullets, I have confidence in it as a reliable game cartridge. It is certainly a contender as one of the most versatile and useful cartridges for hunting all North American species under a variety of conditions and terrain.

There has been much speculation as to why Winchester moved the shoulder forward when designing this cartridge. Regardless of the reason, it resulted in greater case capacity and velocity than that of the wildcat .30-338 or .308 Norma cartridges. This design feature resulted in a comparatively short neck that is around .264-inch long, making it shorter than its .308 caliber, resulting in some criticism. Many cartridge designers prefer the neck to be at least as long as the caliber, which theoretically offers more consistent bullet pull, better bullet alignment with the bore, etc. In es­sence, its short neck has been accused of decreasing accuracy, but the .300 Winchester Magnum has been accurate in the dozens of sporting rifles I have tested, developed handloads for and hunted with. It has also racked up many long-range match wins at 1,000 yards, which is a real test of a cartridge’s accuracy, and the fact that the military uses it for long-range work has largely dispelled this criticism.

It is true that with the short neck, longer bullets (those typically above 200 grains) that are seated to industry overall lengths will extend into the case body and reduce powder capacity, but that is true with any bottleneck rifle cartridge. In other words, regarding cartridges with longer necks, bullets may not protrude into the case body, but they still use powder capacity by seating deeper into the neck.

As can be seen in the accom­­panying handloading data, bullets ranging in weight from 110 to 240 grains were used, and there were no problems associated with the heavier versions that protruded below the case neck and into the case body. The fact remains that the .300 Winchester Magnum offers a ballistic advantage over the .30-338 or .308 Norma Magnum and with correct loads certainly approaches .300 Weatherby Magnum performance.

Velocities of today’s factory loads have been reduced from early advertised figures. Referencing current traditional lead-core jacketed bullets from Federal, Remington and Winchester, 150-grain bullets are generally listed at around 3,290 fps, 180s at 2,960 fps and 200 grainers at 2,700 fps (with no listings for the traditional 220-grain roundnose). However, with new bullet technology and advancements in powders, some companies have been able to boost those velocities by 50 to 160 fps while staying within pressure guidelines. In checking the velocities of several factory loads, as can be seen in Table I, bullet velocities are generally close to advertised figures.

The .300 Winchester Magnum (left) has the same
maximum overall cartridge length as the .30-06 (middle),
which is listed at 3.340 inches, but the .300 is based
on the .375 (right) and .300 H&H Magnum case.

I have extensive experience with the .300 Winchester Magnum and have used it in a variety of rifles from Winchester, Ruger, Remington, Browning, Husqvarna, Sako, P.O. Ackley, Interarms, Kimber, Kimber of Oregon, Colt, Weatherby and others. Notable favorites include a Winchester pre-’64 Model 70 Alaskan (25-inch barrel) and a Browning FN Mauser High Power that can each stack five bullets from handloaded ammunition into groups that can be covered with a dime. Each of the above rifles produced in many different countries have also proven accurate.

A Ruger M77 MKII with blue finish was chosen to develop all the handloads tested for this ar­ticle, while a Ruger M77 MKII Stainless rifle that produced ballistically identical velocities was used to check the velocities of factory loads. My reasons for choosing the Ruger are simple. There are more accurate rifles, but since Ruger began making its own hammer- forged barrels back in the 1980s, their accuracy is generally good, especially with handloads. The primary reason is that when developing extensive handload data, thousands of rounds are fired, which is far more than most rifles get fired in their lifetime, and occasionally pressures can exceed maximum, or an odd powder and bullet combination can produce erratic pressure curves (all of which has been eliminated from the table). I have had such loads damage the extractor and even the ejectors of less robust actions, but the Ruger action is tough as nails and nearly bulletproof. Extractors won’t break from a load that is excessive, and it will vir­tually always extract the case, and neither will the blade ejector become damaged. The action, es­pecially the MKII, may best be described as “Ol’ Reliable,” and in the event of a ruptured primer or case, both of which I have had happen, the gas venting system gets an A-rating for shooter protection.

Maximum case length is 2.620 inches.

While there are different ways to measure water capacity, I prefer to fill the case level with the mouth of a fully sized case. In testing various cases from Federal, Hornady, Norma, Nosler, Remington and Winchester, there was almost a 3-grain capacity variance, which even varied similarly from cases of different vintages from the same manufacturer. I managed to purchase a large quantity of new Winchester cases that are of one lot number, and they were used exclusively throughout this testing. Water capacity was 92.6 grains.

Practically all rifle manufacturers use a one-in-10-inch barrel twist for the .300 Winchester Magnum – with Husqvarna using a one-in-12-inch twist. This twist generally stabilizes bullets ranging from 110 to 220 grains, including practically all hunting and most match bullets. However, Sierra offers a 240-grain HPBT Match bullet that is best stabilized with a one-in-9-inch twist, or possibly faster.

The selection of suitable .30-caliber bullets for handloading the .300 Winchester Magnum is far too vast to include them all, or even discuss in detail the performance of those included here. Regardless, this huge bullet selection adds to the cartridge’s outstanding versatility. Handloaders can choose a bullet and tailor loads to best accomplish a specific task. For example, hunters pursuing game such as moose, Alaskan brown bear, African plains game, etc., will do well to consider tough premium bullets designed for deep penetration, such as the Barnes TSX, Hornady GMX, Nos­ler Partition, Swift A-Frame, Trophy Bonded Bear Claw, etc. For smaller species such as deer and similar-sized animals, less robust and faster bullets with controlled expansion can be excellent choices. Examples include the Hornady InterBond and SST, Nosler Ballistic Tip and AccuBond, Sierra Game­King, Swift Scirocco II and similar bullets.

These .30-caliber magnum cartridges include the (1) .300 Winchester, (2) .300 Remington SAUM,
(3) .300 WSM, (4) .300 H&H, (5) .308 Norma, (6) .300 Weatherby Magnum, (7) .300 RUM
and the (8) .30-378 Weatherby Magnum.

Throat length varies considerably among rifles chambered for .300 Winchester Magnum. Many match competitors seat bullets to just contact the leade, but this practice should not be employed with hunting ammunition, as I have seen bul­lets pulled from the case that stick in the barrel when a round is extracted from the chamber. Bullets should be seated off the leade by at least .010 inch or more. It should be noted that as a result of ogive profile variances, some bullets will contact the leade if they are seated to the industry maximum cartridge length of 3.340 inches, so carefully checking a given bullet is important to assemble reliable hunting ammunition. It will be productive to experiment with bullet seating depth to find that “sweet” accuracy spot for a given rifle, which is not always as close to the rifling as is possible. As a tip, the Barnes TSX will almost always produce its best accuracy when seated around .050 to .090 inch off the leade, and I have seen other bullets produce best accuracy with similar seating depths.

Generally speaking, a large rifle magnum primer should be used, with the Federal Gold Medal Match GM215M used herein. The .300 Winchester Magnum contains enough powder that in order to achieve reliable ignition under all temperatures, humidity changes, etc., a magnum primer is generally advised for handloaders. I have experimented with standard primers too. Interestingly, when using the Nosler 180-grain AccuBond with the Federal GM210M primer and 72.5 grains of Winchester 780 Supreme Ball powder, it reached 2,931 fps and had an extreme spread of 16 fps, while the same load primed with a Federal GM215M primer reached 2,904 fps and had an extreme spread of 53 fps. Switching to IMR-4831 (extruded) powder, the results were reversed. For example, 74.0 grains recorded 3,054 fps with the GM210M primer while the GM215M reached 3,090 fps. The differences in velocity spreads were insignificant at 18 and 21 fps, respectively. (The above loads were fired in a custom Remington Model 700 with a 24-inch Douglas barrel.)

Match shooters who compete during warmer temperatures may recognize lower extreme spreads and increased accuracy with standard primers. It should also be noted that some ammunition companies offer .300 Winchester Magnum loads with large rifle standard primers, but they use sophisticated lab equipment to thoroughly test re­liability, ignition and performance with a particular powder and bullet combination, something the average handloader does not have access to. For these reasons it is suggested to stick with magnum primers for reliable ignition under temperature swings that might include African heat or late season Rocky Mountain subzero temperatures.

The list of suitable powders for the .300 Winchester Magnum seems endless and includes extruded and spherical options. Extruded powders that produced top-notch performance (accuracy and ve­locity) include Hodgdon H-4350, H-4831, H-1000; Alliant RL-17, RL-19, RL-22, RL-25; IMR-4350, IMR-4831, IMR-7828ssc; Norma MRP; Vihtavuori N165 and N560; and Accurate 4350. There have been some excellent slow-burning spherical powders offered in the past de­cade or more with notable performance from Alliant 2000-MR (light bullet loads only), 4000-MR, Accurate Magpro, Ramshot Magnum and Hunter. Suggested “start” loads containing spherical powders should not be reduced, or erratic ignition and pressures are likely. The faster burn rate powders are best when matched with lightweight bullets while those with a slower burn rate perform best with heavier bullets.

Many loads that produced inferior accuracy were eliminated from the load table. On the other hand, many of the listed loads consistently produced sub-MOA accuracy from the Ruger rifle. Often the best accuracy was recognized with loads that were maximum or near maximum.

Industry maximum average pressure has historically been listed at 54,000 CUP, but with the transition underway to the significantly more accurate piezoelectric transducer system, that figure has been changed to 64,000 psi. Most factory loads are below that figure and typically measure around 57,000 to 61,000 psi, although that can vary with lot numbers, man­ufacturer, etc. None of the accompanying data exceeds industry pressure limits.

In studying the compiled data, it is reasonable for handloaders to duplicate or even exceed factory-load velocities. With a huge bullet selection, it is clear why the .300 Winchester Magnum is a contender as one of the best all-around cartridges for hunting all game in North America.