Big Bore Compendium – .577 Tyrannosaur

In the days that the British ruled most of huntable Africa, the magic velocity for dangerous game hunting was considered to be 2150 feet per second. During the past 30 years the game has changed, however, and sportsmen demand ever more from their rifles. Now in order to assure adequate penetration from every angle, the conventional wisdom is that a cartridge should generate 2400 feet per second.

The 577 Tyrannosaur is a modern day attempt to blend the giant .585 diameter 750 grain bullets of the 577 Nitro Express with the magic velocity of 2400 feet per second. The result is a brutish rifle that is nearly uncontrollable. Another consideration is that monolithic solids should be used in this cartridge because bullets of a convention design meant for 577 Nitro Express velocities will likely rivet or break apart at 577 Tyrannosaur velocities. One Norwegian hunter shot an elephant in the spine using a .577 Tyrannosaur loaded with Woodleigh 750 grain solids. The Woodleigh riveted and fishtailed, as it had been pushed beyond its design criteria.

For the sportsman interested in building a custom rifle for the 577 Tyrannosaur, only a magnum length (3.800″) magazine box will suffice, thus ruling out model 70’s and Mauser 98’s. Further, the enormous diameter of the case rim (0.688″) requires either a P14 Enfield bolt, or at least a 0.750″ bolt body diameter. Magazine box and follower construction as well as rail and ramp modifications to the action will all be completely custom and should only be attempted by the most skilled big bore specialist. Brass and ammo for the 577 Tyrannosaur are even more expensive and harder to find than for the 577 Nitro Express. Although the 577 Tyrannosaur can be loaded down to reduce its horrendous and almost uncontrollable recoil, the .585 Nyati would be a better choice for lower velocity loads since it burns less powder and therefore will produce less recoil. Factory rifles in .577 Tyrannosaur are available from the A-Square Company of Kentucky. Custom gunsmith Joe Smithson of Provo, Utah offers fine custom rifles in .577 Tyrannosaur based on the Granite Mountain action.

Example loads:

Cartridge Powder Primer Bullet Velocity Notes
577 Tyrannosaur 170.0 grains IMR4350 F215 750 solid 2480 f.p.s.