November 01, 2021
There are a host of fine cartridges to pick from if long range shooting is your game. The various 6mms are hugely popular, as are the 6.5mms and then you have the various 7mms and even the .338s. One very versatile cartridge to consider though is the .300 Winchester Magnum, often simply referred to as the “Win Mag”. If you are looking to do more than simply ring steel, the .300 Win Mag has a lot going for it. It will deliver a substantially larger and heavier payload onto your target than the smaller calibers. So, it’s a fine choice for big game hunting. Yet it will do it without destroying your bank account like the .338 Lapua Magnum, and other exotics, are capable of. A very flexible cartridge, I thought it would be interesting to take a closer look at the old .300 Win Mag, both the good and the bad.
The .300 Win Mag was introduced by Winchester Repeating Arms Company way back in 1963. It was preceded by the .264 Win Mag, .338 Win Mag and .458 Win Mag which were all unveiled in 1958. All three of these cartridges were based upon a modified .375 H&H Magnum case. The parent case was blown out and shortened to 2.500 inches. The 2.500 length is significant as it allowed it to function through a standard length rifle action. Roy Weatherby had popularized this length beginning in 1943 with his .270 Weatherby Magnum. Winchester followed this lead when they developed their own line of magnum cartridges.
However, when Winchester finally introduced a .30 caliber magnum cartridge they didn’t simply neck their .338 Win Mag down. Rather than doing the obvious they instead tweaked the case design a bit. Namely they moved the shoulder forward 0.156 inch which increased case capacity, but also gave it a relatively short neck. The result of their work was a large belted magnum with a case length of 2.62 inches. Rim diameter is .532 inch while base diameter is .513 inch. Shoulder diameter is .489 inch and overall cartridge length is 3.34 inches. Maximum SAAMI recommended pressure is 64,000 PSI. Since its introduction the .300 Win Mag has gone on to become the most popular of all the various .30 caliber magnum cartridges by a large margin.
Why has the .300 Win Mag reached and maintained such popularity? For a combination of very simple and straightforward reasons. Namely it offers a useful step-up in terminal performance over standard cartridges like the .30-‘06 for hunters. It will kill anything which needs killing in North America, and do it in a standard length action. Long-range shooters appreciate both its exterior ballistics and match-winning accuracy at 1,000 yards and beyond. Plus from the start it was intended for the blue collar worker rather than being an expensive snob round. So, loaded ammunition and components are relatively affordable compared to many other magnum cartridges.
Despite all this praise the .300 Win Mag is not without its fair share of faults. Due to Winchester pushing the shoulder forward, the .300 Win Mag has a very short neck. It is actually shorter than the caliber of the bullet loaded into it. Many have criticized this feature, claiming a short neck would not hold a bullet in proper alignment with the axis of the bore. Others have criticized it claiming it provided insufficient tension on the projectile to adequately retain it. This issue is said to be exacerbated by the need to seat heavier bullets very deeply to maintain the .30-’06-like 3.34 inch OAL. Deeply seated bullets will, of course, also eat into the .300 Win Mag’s case capacity.
Then there is the belt. A distinctive feature of Winchester’s .264, .300, .338 and .458 Magnum cartridges, it is little more than a holdover from the British cartridge they are based upon, the .375 Holland & Holland Magnum. However, it should be kept in mind the justly famous .375 H&H Magnum was first introduced in 1912 as the .375 Belted Rimless Nitro-Express. It is old enough to have been originally loaded with cordite and was only the second cartridge to feature a belt. On a long tapered case intended for dangerous game hunting, during this specific period in time, the belt made sense. In the late 1950s it was a useful marketing tool to catch the attention of the American sportsman. On the comparatively straight wall .300 Win Mag in the 21st Century it is nothing more than a nuisance.
Although the .300 Win Mag is designed to headspace on the belt, very few reloaders actually do this. Belt thickness can and does vary, especially from manufacturer to manufacturer. More consistent accuracy can be achieved by headspacing off the shoulder. Reloaders can accomplish this by simply backing their resizing die off ¼ to ½ turn. This should also extend case life. When carefully loaded a quality Win Mag is capable of excellent accuracy at 1,000 yards and beyond. Its accuracy and ability to buck the wind has endeared it to many competitive shooters and it has won its share of 1,000 yard matches.
All that performance does come at a price though. Recoil tends to be on the attention getting side on a rifle without a muzzle brake. My friends and I would joke about a stiff .300 Win Mag load ‘lifting one’s elbows off the mat’. While reality isn’t quite that bad, the big Win Mag will fatigue a shooter out faster during a long string of fire than lighter calibers. Hand in hand with the stiff recoil is throat eroding performance. If you want to go fast you have to pay the piper. In this case it’s not only a pound of your flesh but also a healthy scorching of your barrel’s throat. Do not expect to stuff copious quantities of slow burning powder down a .30 caliber hole and have Methuselah-like barrel life. If you demand maximum performance peak barrel life may only be 1,200 to 1,800 rounds. So what’s my point? Simply that the .300 Win Mag isn’t perfect.
The exterior ballistics and terminal performance of the .300 Win Mag were not lost on the US Military. It soon became popular with the various rifle teams for use in competition. In addition, the Navy in particular took an early interest in the Win Mag as a means to extend the range of their snipers. Basically they wanted something with more ‘zing’ than a 7.62mm NATO was capable of, but without the signature and size of the .50 BMG. They originally began using a 185-grain Lapua FMJ-BT, but eventually switched to a 190-grain Sierra MatchKing. Target velocity was 2,950 fps. During development of what came to be known as the A191 load (type classified as the Mk 248 Mod 0) much work was done on the chamber design (headspacing off the shoulder, not the belt) as well as maintaining a consistent velocity over a wide temperature range.
The result of this work was a flat shooting and hard hitting sniper cartridge with 200 to 400 yards of extended reach compared to the 7.62mm M118. With a flatter trajectory and less wind drift the .300 Win Mag offers a useful step up in performance in a similar size rifle. It does this while keeping recoil and muzzle signature similar to the 7.62mm. Combat performance of the .300 Win Mag has been very good. The US Army eventually decided to retain their M24 rifles by converting them to .300 Win Mag. With the coming of the semi-automatic 7.62mm M110 sniper rifle, units were originally told to hand in their bolt action M24s. This didn’t go over well with a war-time army. So the decision was made to convert the 7.62mm M24 and utilize it as a bridge to a more advanced design. The conversion was straight forward as the M24 had been originally designed with this capability in mind.
With the US military embracing the .300 Win Mag, work was undertaken to further improve it. The A191/Mk 248 Mod 0 was refined and a new Mk 248 Mod 1 load introduced. This new load was developed to stretch the .300 Win Mag’s reach even further. The traditional 190-grain Sierra MatchKing was replaced by a 220-grain MatchKing. Doing so bumped the G1 Ballistic Coefficient from .533 to .629. Despite the heavier projectile muzzle velocity remained very similar. This was accomplished through a very heavy charge of H1000 powder which is pushing pressures slightly above SAAMI levels. As the Mk 248 Mod 1 is loaded to a longer OAL than SAAMI specifies it may not be safe in some commercial rifles. The end result is an effective long range sniper load.
But what about your needs? If you have fancied a .338 Lapua Magnum, but vapor locked at the price of ammunition, consider a .300 Win Mag. Loaded ammunition, dies and components are all readily available. Ammunition, even match loads, is significantly less expensive. Brass is plentiful from a variety of domestic and foreign manufacturers. Federal, Remington, Nosler, Hornady, Norma and Winchester all offer brass. Winchester brass is relatively inexpensive while Norma brass has earned a reputation for excellent quality. Just keep in mind that brass will vary in weight and volume from manufacturer to manufacturer. It can also vary depending upon the lot and date of manufacture.
There are a number of fine powders which work well with the .300 Win Mag. IMR 4350 is a traditional ‘Old School’ favorite which remains popular. Hodgdon’s H1000 and Retumbo both have their followers. If you are a fan of VihtaVuori powders one I recommend trying is N560. RL-22 is also an excellent powder to try. The important thing is to start well below max and slowly increase your charge weight while carefully watching for pressure. You will also need to decide how fast you wish to run your handloads. This can be a balancing act. The faster the load the better the exterior ballistics, but the harder it will be on your barrel.
Seeing as the Win Mag utilizes standard .308 diameter projectiles there are a host of fine choices available. Hornady, Berger, Sierra, Nosler, and Lapua all offer multiple designs to consider. I will say that Sierra’s 19- grain MatchKing is well known for being relatively easy to get to shoot well. Many of the VLDs can be a bit touchy regarding OAL, and can take a bit more effort to dial in. If you are shooting past 1,000 yards though, the extra effort can be well worth it.
To show what a .300 Win Mag is capable of I put mine to work on the range. It is a Tactical Rifles build using their Chimera Magnum length action. Riding inside this is a fluted bolt with an oversize knob. Bottom metal consists of their own design which accepts detachable AI magazines. The trigger is adjustable, and out of the box was excellent being both very light and crisp. Fitted to the top of the action is a one-piece steel M1913 rail. Mated to the receiver is a 24 inch long heavy stainless steel match barrel. The chamber on this was cut to minimum SAAMI specifications. Twist is 1-9.25 inches facilitating use of very heavy 208-230 grain bullets. A Tactical Rifles’ three baffle brakes is fitted. The barreled action was dropped into their distinctive T-7 rifle stock. An IOR 6-24x56mm scope was mounted during testing.
Test ammunition was loaded by our Gunsmithing Editor Gus Norcross and is a duplicate of the National Guard Marksmanship Training Unit’s (NGMTU) 1,000 yard Camp Perry load. It consisted of a 190-grain MatchKing over a healthy dose of IMR 4350. This posted a best of .19 inch at 2,832 fps and averaged .3 inch for four 5-shot groups at 100 yards. At 800 yards this load averaged four inches at 800 yards in favorable wind conditions. My best five shot group measured just 3.5 inches at 800 yards. This is a very “old school” load using a very traditional bullet.
There are many excellent cartridges to choose from for long range shooting. The .300 Win Mag is just one to consider. Like all of them it has its strengths and weaknesses, good and bad. A true American classic, it is capable of impressive performance. The latest generation of very efficient match bullets only makes it better.
If you have any thoughts or comments on this article, we’d love to hear them. Email us at FirearmsNews@Outdoorsg.com
About the Author:
David M. Fortier has been covering firearms, ammunition and optics since 1998. He is a recipient of the Carl Zeiss Outdoor Writer of the Year award and his writing has been recognized by the Civil Rights organization JPFO. In 2007 he covered the war in Iraq as an embedded journalist.