Wow, it's been a while since I last posted. Time flies when you're constantly inundated with high profile IT projects... Anyway, on to the topic at hand!
Unless you've been ignoring the gun market in the past decade (or more), you probably noticed a large jump in popularity of "Modern Sporting Rifles" or MSRs, which generally refers to AR-15 and AR-10 style rifles. I'm about as strong-willed as the next gun nut when it comes to new toys, so I couldn't help but become interested in MSRs, too. I assembled my first one a couple years ago in the oh-so-typical 5.56/.223 chambering. Now I'm looking at the other options that promise to take this rifle beyond its "mouse gun" stereotype.
Whenever a certain action type gains enough popularity, cartridge design tends to follow. This happened with the .308-sized "short" action, the .30-06-sized "standard" action before it, and many others before that. What I'm going to look at in this post is three cartridges that push the little chamber to its limit: the .450 Bushmaster, .458 SOCOM, and .50 Beowulf.
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.450 Bushmaster
The .450 Bushmaster was developed jointly between Tim LeGendre of LeMag Firearms, Bushmaster, and Hornady a few years ago (formally introduced in 2007, I think). It is derived from LeGendre's previous .45 Professional cartridge, which in turn was a modified .284 Winchester case. Because of the involvement of established companies such as Hornady and everything under the Freedom Group banner (Bushmaster and Remington, specifically), this is the most widely available in terms of guns and factory ammunition availability (but not necessarily variety) of the three cartridges I'm covering here.
The Bushmaster cartridge itself falls between the .454 Casull and .460 S&W Magnum in overall length, and also, perhaps, for performance. The bullet diameter is .452" which it shares with pretty much every .45 caliber handgun cartridge in production today. This does limit bullet selection (and, in my mind, its usefulness) somewhat, especially on the heavier side of the spectrum.
Hornady's factory ammunition for the .450 Bushmaster utilizes a 250 grain FTX bullet with a listed muzzle velocity of 2214 fps and 2722 ft-lbs of energy (20-inch barrel). Remington lists a Premier AccuTip load with a 260 grain bullet at a muzzle velocity of 2180 fps and 2743 ft-lbs of energy. If you don't handload, this pretty much sums up your ammunition options. The performance is very similar to the .460 S&W Magnum, though the .460 does it from a pistol because of the higher pressures involved.
Reloading data isn't too widely available yet, though I'm sure new editions of reloading manuals will include it (especially Hornady's). "Rolling your own" is the only way to get 300+ grain bullets in the Bushmaster currently, but it might be worth your trouble if you want to expand the usefulness of the cartridge.
.458 SOCOM
The .458 SOCOM was developed by Marty ter Weeme of Teppo Jutsu in 2000. It was developed using lengthened .50 AE brass, necked down to .458", and with a somewhat more rebated rim. Rim diameter is .473" which is the same as the .308, .30-06, and quite a few other Mauser-based rounds. One of the design considerations I find most interesting is that it will function in any standard AR-15 magazine, which the other two cartridges examined in this post do not (note: the .450 Bushmaster can be used in standard mags in a pinch, but can have feed issues when doing so).
Performance is generally described as on par with factory .45-70 loads. A typical 300 grain .45-70 load has a factory-listed muzzle velocity of just over 1800 fps and just over 2100 ft-lbs of energy, which the .458 SOCOM matches or exceeds a bit with factory loads. The fact that the SOCOM uses .458" bullets (same diameter as the .45-70, .458 Winchester Magnum, pretty much all .45 caliber rifle rounds) means that it has a much wider range of weight selection than the Bushmaster.
The .458 SOCOM has mostly been stuck in a wildcat/proprietary status, though it does have one of the major AR makers, Rock River Arms, manufacturing rifles so chambered. Ammunition is available from Cor-Bon and SBR Ammunition in bullet weights ranging from 255 grains to 500 grains.
Reloading will gain you access to more of the potential of this round, as long as you can find reliable data. Bullets commonly available range from 250 grains all the way up to 600 grains. Yes, the .458 SOCOM can utilize the 600 grain bullets without exceeding maximum length. This would make for a very interesting subsonic load, especially where suppressors are legal.
.50 Beowulf
The .50 Beowulf was designed by Bill Alexander of Alexander Arms and introduced to the public circa 2002. It is essentially a lengthened .50 AE case with a further rebated rim. The rim diameter (.445") is the same as the Russian 7.62x39 round because it allows for a manageable bolt size to be used in the AR platform.
In comparison to other .50-caliber cartridges, the .50 Beowulf really performs like a modernized .50-70 Government, and I'm certainly not the first to draw that comparison. 400-grain loads between the .50-70, the ..50 Beowulf, and the .500 S&W Magnum all have muzzle velocities around 1800 fps. The important factor here is that the .500 S&W does it from an 8.375" barrel while the others were measured from 24"+ rifle barrels. Again, high operating pressure does wonders.
Dimensionally, the Beowulf is a straight-walled cartridge with a case length slightly longer than the .500 S&W Magnum and slightly shorter than the .50-70 Government. Bullet diameter is .500, which is the same as the typical .50 caliber handgun cartridges (.500 S&W Magnum, .500 Wyoming Express, and .50 Action Express, for example), but not the .50 caliber rifles which tend to be .510" diameter or larger (the .50-70 Government uses .515" bullets).
Ammunition is available from Alexander Arms in several bullet weights ranging from 300 grains to 400 grains. They also provide reloading data on their site for most of the common .50 caliber bullets out there, including a 530 grain bullet originally meant for muzzleloaders.
Opinion/Conclusion
So, if I were to put these in order of most interesting to least interesting, this would be my list:
1. .458 SOCOM
2. .50 Beowulf
3. .450 Bushmaster
Why? Because the .458 SOCOM has the most versatility in loads, Rock River Arms has great accessory options on their site for rifles and uppers in .458 SOCOM, and it's designed to feed through standard AR-15 magazines (plentiful and cheap). Not exactly huge advantages over the other two, but enough to edge them out in my mind.
The .50 Beowulf is a pretty close second, and I'd definitely be willing to reconsider if Alexander Arms' rifle prices dropped a bit. Bullet selection is a little limited, and factory ammo is basically at proprietary status, but reloading data is easily found and all the components are available through the Alexander Arms site.
Truthfully, the .450 Bushmaster just isn't what I'm looking for. When you want a short-range "thumper" cartridge, bullet weight is a big selling point (you know, so you can hunt big game), which is why I'm disappointed that the only factory loads out there have 250 and 260 grain bullets. The use of ballistic tips is also misleading, because it might cause someone to think the bullet will have a flatter trajectory, which it won't. The bullets are still short, stubby, and have a low ballistic coefficient (approximately .210). Unfortunately, because of the pistol bullet diameter, really heavy bullets are out of the question. Hey, Bushmaster, why not just market an AR-10 chambered for .358 Winchester? You'd get better-performing 250 grain loads, and my immediate attention!
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