Michael Scherz specializes in building the most massive of big-bore rifles, such as the .505 Gibbs, on the large magnum CZ action using a custom-made oversize bolt for greater strength and more reliable feeding. He also offers the CZ 550 Magnum action alone, bored out with oversized bolt, fitted and installed for other custom rifle makers to use as the basis for their own African rifles.

Having more bolt face to support the super-large cases is easy enough to understand, but enhanced feeding reliability? Scherz explains:

           “The really big cartridges, like those based on the big Gibbs and Rigby cases, sit lower in a staggered magazine box than smaller diameter cartridges. Sometimes, as the bolt moves forward to strip the cartridge from the magazine, the front of the cartridge tips up into the chamber and the back of it tips down so that the bolt rides right over the case and loses it. That's why Weatherby and some others have done single-stack magazines.

           That's why Fred Wells and some other high-end custom action makers went to a .750” bolt for the big cartridges. If your bolt's bigger around it sits down lower in your receiver and has a broader area to pick the cartridge up out of20the magazine. Even the .500 Jeffery, which doesn't need a thicker bolt-face because of its rebated rim, is still a fat piece of brass. A larger diameter bolt helps strip it out of magazine with a lot more reliability. It's no trick to bore out a standard CZ receiver and put a bolt in it that's a few thousandths larger. It doesn't weaken the receiver and doesn't have any effect on the locking lugs. It just makes everything work better."