November 23, 2021
In 1912 the respected British firm Holland & Holland established the future of the belted rifle case with the .375 H&H Magnum. It was not the first belted case, but it was the one that set the dimensions for a century of cartridges to come. H&H’s head and belt design have been used almost unchanged in a staggering number of standard, proprietary, and wildcat cartridges.
In about 1920, H&H applied those head dimensions to a then-new .30-caliber cartridge, first called the “Holland’s Super 30.” The same length as the .375 H&H case, the newcomer had a long, tapered shoulder. Soon its standardized name became the .300 H&H Magnum, and there was a sound reason for that funny-looking shoulder.
I’ve previously written about how handloaders can deal with belted rifle cases, but not so much on why they had to exist. First, let’s reconsider “Magnum” and “belted” for the benefit of our younger or newer readers.
To many shooters, “belted” and “magnum” are conjoined twins, but that cannot be further from the truth. “Magnum” is a non-technical, marketing term. It may imply a performance improvement, but that improvement does not have to be real.
Conversely, the belt has a compelling technical reason to exist. It is a raised ring at the head end of a cartridge case lying where the extraction cannelure meets the case body. The magazine bolt-action rifle and the British love affair with Cordite propellant drove H&H to develop this case.
Magazine rifles function best with rimless cartridges, but those cartridges need a rim substitute for headspacing. Typically, that is a pronounced case shoulder or the cartridge’s case mouth. However, if the bullet will be crimped as with most factory ammo, the case mouth can’t be used. So why not simply use enough shoulder?
That is where the Cordite connection entered. Cordite was an early, high-nitroglycerin-content smokeless propellant. It came in long sticks roughly the diameter of a pencil lead that is cut to a length that fits between the inside of the case head and the base of the bullet or sometimes an over-powder wad. You didn’t pour this stuff into a case; you inserted a bundle of sticks.
The need to insert Cordite bundles resulted in many British-developed cartridges having cases with shoulders that are either a narrow width—like the
.375 H&H—or a shallow angle like the .300 H&H. The latter’s shoulder angle is only 8.5 degrees. Compare that to the .30-06 shoulder at 17.5 degrees.
The 90-degree leading edge of the belt becomes the headspace surface, nicely supporting the case against the blow of the firing pin for reliable ignition. It remains unobtrusive and feeds reliably in magazine rifles.
People think the belt adds case strength at a critical point. I don’t. The critical point is ahead of the belt. I’ve seen belted cases just as mangled as non-belted ones when suffering an 80,000-psi overload.
The .300 H&H was first loaded in the United States in about 1925, but shooters had to wait another decade for a domestic rifle chambered for it: the Winchester Model 70 Super Grade. The .300 H&H supplanted the .30-06 as the most powerful commercially loaded U.S. .30-caliber cartridge. Original H&H specs were close to 3,000 fps.
The .300 H&H ruled the .30-caliber world until the .300 Weatherby came out in about 1944 and held its own for another 20 years until the .300 Winchester Magnum edged it out. Today, the H&H’s published nominal velocity with 180-grain bullets has been downgraded to about 2,900 fps. With safe handloads and current propellants in 24-inch barrels, it can still drive a 180-grain bullet to just over 3,000 fps.
There are not a lot of tricks to handloading the .300 H&H. The complicating factor is cartridge overall length (COL) in custom rifles. COL is a function of both action length and how the chamber’s throat and the bullet’s profile marry up. Custom rifles don’t have to follow industry guidelines. The standard chamber throat drawing shows no freebore and a 2-degree leade that is 0.114 inch long. The industry COL is 3.600 inches; the sample cartridge pictured has a match bullet seated to max COL. It chambered easily in one custom rifle but contacted the rifling in another.
Custom .300 H&H rifles have been built on an array of bolt-action lengths. Some may not eject a live round that is within COL values and chambers normally. With so many custom rifles for this cartridge, the saying, “COLs are guidelines, not gospel,” is important to remember. Determining proper COL for your rifle is your job.
The .300 H&H’s 3,000 fps velocity and more than 3,500 ft-lbs of energy with safe handloads is impressive performance, even considering the handful of newer .30-caliber cartridges that exceed those marks. Not bad for a century-old hunting buddy.