A few years back I traded by way into a beautiful Extreme Big Bore .457. Apparently this was one of the last made in Michigan before the sale of the platform to TX. it was a strange combo, a somewhat random 26.5" barrel. Perhaps it was all that was left to build that last rifle, I dunno? I didn't really care for the valve, hammer spring, nor hammer weight combination so in went a peek poppet and different hammer and springs. Ultimately this yielded more energy and tighter ES than as built in Michigan. Later it was found to have a badly machined muzzle and throat/lead, forcing a barrel swap. I purchased 32" of TJ's 45-70 barrel.
Fast forward 3 years and I am finally able to assemble the gun with its 32" barrel. The gun was designed around 4500psi fills, which I still find to be a bit wasteful, so my focus has been on a 3000psi fill. Making a gun built around max energy 4500psi to perform at 3000psi involved cutting weight from the hammer, reducing hammer travel, and reducing hammer-induced valve lift. There are other methods to accomplish this task, this is just the path I chose...
Currently I have a 4 shot 3000psi tune resulting in 925, 950, 920, 880fps when shooting bobs boattail 220gr hollowpoints.
Swapping back to the OEM hammer and OEM spring, a 4500psi fill produced 3 shots of NSA 302gr at 980, 921, 846fps, ending at 3000psi.
Next steps are to lug it down with heavy ammo and see how much energy it can produce at 3000 and 4500psi.
Those that have previously traveled this road, please share your experiences.
Fast forward 3 years and I am finally able to assemble the gun with its 32" barrel. The gun was designed around 4500psi fills, which I still find to be a bit wasteful, so my focus has been on a 3000psi fill. Making a gun built around max energy 4500psi to perform at 3000psi involved cutting weight from the hammer, reducing hammer travel, and reducing hammer-induced valve lift. There are other methods to accomplish this task, this is just the path I chose...
Currently I have a 4 shot 3000psi tune resulting in 925, 950, 920, 880fps when shooting bobs boattail 220gr hollowpoints.
Swapping back to the OEM hammer and OEM spring, a 4500psi fill produced 3 shots of NSA 302gr at 980, 921, 846fps, ending at 3000psi.
Next steps are to lug it down with heavy ammo and see how much energy it can produce at 3000 and 4500psi.
Those that have previously traveled this road, please share your experiences.