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Mini Compendium of Big Bore Cartridges

by Daniel McCarthy
© 2004

550 Magnum

The 550 Magnum is a new cartridge designed by Neal Shirley of Yuma, Arizona that is generating a lot of excitement. It is based on the 460 Weatherby cartridge necked up to .550" bore diameter. The 550 Magnum will push a 700 grain bullet close to 2400 f.p.s. if the shooter can stand behind the rifle.

3 easy conversions: From left to right, 500 A-Square, 550 Express and 600 Overkill. The 500 A-Square and 550 Express are very easy and economical conversions to perform on a CZ550 in 416 Rigby. Little more than a new barrel and bedding are needed, with very minor rail and ramp adjustments. A CZ550 is also very easy to convert to 600 Overkill if it is sent to American Hunting Rifles where a single stack magazine box is installed that feeds fast and slick. For shooters looking for something big and easy, these 3 are the way to go.

By basing the 550 Magnum on 460 Weatherby basic brass, the historic problems related to rebated rims and/or brass of questionable quality in the 500 Jeffery, 505 Gibbs, 500 AHR and .585 Nyati are eliminated. The round will fit into a CZ550 action economically and with very little modification. The 550 Magnum pushes a 700 grain bullet at 2400 feet per second, creating a very deadly dangerous game round.

A short version of the 550 Magnum called the 550 Express will fit into Mauser 98 and Winchester model 70 actions. It has a 2.65 inch case and a 3.35 inch cartridge overall length so that it will fit into any action that accommodates a .338 Win. Mag. or .458 Win. Mag. It will be a true delight to be able to push 700 grain bullets at 2200 f.p.s. from surplus military Mauser 98 actions.

The 550 Magnum and 550 Express have a unique groove diameter of 0.550", shared only by a few obsolete cartridges. Consequently the bottleneck for 550 Magnum owners is a steady supply of top quality solids for dangerous game hunting. At the time of this writing, Mr. Shirley has gotten several premium bullet makers interesting in supplying this cartridge, Alaska Bullet Works, PA Bullets, http://www.CustomCastBullets.com , and Hawk bullets are already in production. Properly headstamped brass is available from Quality Cartridge, and Jamison International - Formerly BeLL Brass http://www.custombrassandbullets.com . Alternatively the reloader can just neck up and fireform 460 Weatherby brass, though it will be slightly too short, requiring the reloader to load to OAL rather than cannalure.

Barrels for the 550 Magnum are available from Dan Pederson of Cutrifle Barrels ( http://www.cutrifle.com ) in Prescott, Arizona, Bausksa Barrels, Pac-nor, and Badger barrels in the US.

For the reloader who wants a practical big bore bolt gun of maximum possible bullet diameter, the 550 Magnum is the natural choice. If you were thinking of a 500 A-Square, 505 Gibbs or 500 Jeffery but wanted a little more bullet, the 550 Magnum provides it. Even Mauser and Model 70 fans can have a low cost big bore by rebarreling to the 550 Express. Custom loaded ammo is available from Superior Ammo.

Example ballistics:

Cartridge - Bullet - Velocity - Notes

550 Magnum - 700 grain - 2400 f.p.s. - Long version for CZ550 and Ruger RSM actions. 26" barrel.

550 Magnum - 650 grain - 2400 f.p.s. - n/a

550 Magnum - 600 grain - 2500 f.p.s. - Low sectional density - not preferred.

550 Express - 600 grain - 2400 f.p.s. - Short version to fit in .458 Win. Mag. sized actions.

550 Express - 650 grain - 2250 f.p.s. - n/a

550 Express - 700 grain - 2200 f.p.s. - Maximum load 23" barrel.

(NE.com disclaimer - use of reloading data provided on NitroExpress.com or by the author is strictly at the user's own risk.)