Big Bore Compendium – .500 A-Square

The 500 A-Square was designed by Art Alphin of the A-Square Company for maximum penetration and shock power on dangerous game. Pushing a 600 grain bullet at 2400 f.p.s., the 500 A-Square is everything that a bolt gun afficianado could want. It uses a 460 Weatherby case necked up to .510″ and slightly improved. The 510 Wells preceded the 500 A-Square by well over 20 years and was designed by Fred Wells of Phoenix, Arizona. Ballistics for the two cartridges are identical and selection of one over the other is merely a matter of personal preference. The 500 A-Square has a cartridge overall length of 3.75″ and due to length will only fit into relatively large actions such as the CZ550. Some may be tempted to rebarrel a Weatherby Mark V or a Sako TRG to 500 A-Square thinking it a cheap and easy route to a big bore dangerous game rifle. Although the debate about controlled feed versus push feed actions is best left to another article, the author would not contemplate use of a Weatherby or Sako for this purpose. Factory rifles in 500 A-Square are available from the A-Square Company of Kentucky. B. Searcy & Co. offers bolt rifles in 510 Wells, as does Fred Wells.

There are a couple of advantages that the 500 A-Square has over the 500 Jeffery, 505 Gibbs and 500 AHR. First, cheap, high quality brass in 460 Weatherby is available from Norma, and necking it up to .510″ is a simple matter. In contrast, brass for the 505 Gibbs and 500 Jeffery can be very expensive and some of it can be of varying quality. Second, the 500 A-Square has a rim that fits easily onto a 0.700″ bolt, making the use of expensive magnum mauser actions unnecessary. In fact, the 500 A-Square is one of the cheapest big bore rifles to build because a CZ550 in 416 Rigby can simply be rebarreled. Then the extractor needs to be tightened, and the rails opened very slightly. There are no simpler big bore conversions. Third, the 500 A-Square does not have a rebated rim, so there are no difficult feeding issues to contend with. Unless the reader insists on being a traditionalist, the 500 A-Square is probably the best choice in .50 caliber dangerous game calibers. Rifles for this cartridge should weigh at least 12 pounds.

A short version of the 500 A-Square called the .495 A-Square is available that is short enough to be build on Winchester model 70 and Mauser model 98 actions, with extensive reworking of the magazine box, rails and ramp.

Due to brass and bullet availability, the 500 A-Square is the most practical cartridge discussed in this article and should be seriously considered by anyone seeking a big bore on a budget. The disadvantage of the 500 A-Square is that it, like the 505 Gibbs, requires a very long action, making the rifle somewhat bulky.

Example loads:

Cartridge Powder Primer Bullet Velocity Notes
500 A-Square 118.0 grains Reloader 15 F215 600 grain 2450 f.p.s.
500 A-Square 115.0 grains IMR 4350 750 grain Hornady bullet intended for the 50 BMG 2150 f.p.s. Requires chamber to be deep throated and for rounds to be single loaded.
500 A-Square 122.0 grains H870 600 grain 1800 f.p.s. Reduced velocity practice load.