If some of you remember from my previous posts on here, my grandfather asked me for help discovering why his Mark V 300 Weatherby - the rifle he's hunted all over North America and even Africa with - had suddenly begun throwing bullets inaccurately. My dad and I borrowed it from him and tried everything we could think of, but nothing I did managed to get the gun shooting with any semblance of accuracy. Groups of 7" or more at 100 yards were the best I could do, no matter what I tried. He and I decided it probably needed a new barrel, but he wasn't all that interested in spending a lot of money fixing a gun he would never use again. His health was failing, and he had quit hunting because of it.
He died in July of 2016, leaving me several guns, including the Weatherby.
I wanted to fix the rifle, I really did, but since I'm a handgun hunter, I was hesitant putting too much time and effort into a rifle with other projects I was more interested in. However, last month my dad and I decided we needed to get it fixed. Before committing to what I thought would end up being a rebarreling project, I took the Weatherby to a gunsmith who lives nearby. He couldn't tell if the rifling was excessively worn down, but he did comment on copper buildup. He also told me the muzzlebrake wasn't a Weatherby brake - it was aftermarket.
At his direction, I disassembled the rifle, removed the muzzlebrake, plugged the barrel, and filled it with a copper solvent overnight, then thoroughly cleaned the barrel. I also confirmed that it is indeed a 1-12" twist, so the 180 grain and heavier bullets would probably not do as well. Last weekend, my dad and I took it out to test it. Using old Federal 180 grain bullets, we got it on paper at 25 yards, then 50, and then finally shot 3-shot groups at 100 yards. The 180s made 4" groups. Then, we tested two handloads I had previously made using 150 grain SSTs, one with a standard seating depth, then one seated long. The result? 1.15" and 1.09" groups, respectively. For one last test, I screwed the muzzlebrake back on tightly. The handloads' groups opened back up to 7".
While I'm somewhat put out with the muzzlebrake being such a detriment to the rifle, I'm ecstatic that I've finally solved this lingering mystery.
