As no one else has asked, I will. Have you fired factory ammo in the rifle or just bought brass, made handloads and shot those If you shot factory, how did those bullets perform.
Not a .35 Whelen but years ago I was given a .243 that the owner said, "If you can make it shoot, it's yours. Otherwise throw it away." It would keyhole bullets at 25 yards regardless of weight. I tgrimmed the muzzle and squared it off before recrowning the barrel, slugged the bore to determine bore and groove diameter, both of which were in specs. Seated bullet so they'd engage the rifling and seated some at various depths all to no avail. One strange thing, the bore looked like a Marlin Microgroove. Marlin did make some rifles on FN Mausers as I recall and I'll bet that's where the barrel on that rifle came from. That one just wouldn't shoot. Even the throat looked good.
I think if the OP's rifle were mine, I'd get a few pure lead sinkers of the proper size and oil the bore and drive a couple down the barrel, one at a time. Three would be even better and use a good micrometer to determine the groove diameter. It should be .357" to .358". I'd examine the crown for any possible damage and I'd definitely check out the twist rate. If it's slower than 1 in 16" then the barrel needs to be replaced. A 1 in 16" will stabilize bullets up to 250 gr. and sometime, though rarely even stabilize 275 gr. bullets.
Currently I have three rifles in .35 Whelen, a Ruger M77RS, a Remington M700 Classic and a custom Mauser. The Mauser has a 1 in 14" twist and the two commercial rifles have 1 in 16" twists. My next planned custom will have a 1 in 12" twist which if I understand things correctly is what was originally used in the Whelen.
There is something radically wrong with that rifle and my money is on the barrel needing replacement.
Paul B.
Not a .35 Whelen but years ago I was given a .243 that the owner said, "If you can make it shoot, it's yours. Otherwise throw it away." It would keyhole bullets at 25 yards regardless of weight. I tgrimmed the muzzle and squared it off before recrowning the barrel, slugged the bore to determine bore and groove diameter, both of which were in specs. Seated bullet so they'd engage the rifling and seated some at various depths all to no avail. One strange thing, the bore looked like a Marlin Microgroove. Marlin did make some rifles on FN Mausers as I recall and I'll bet that's where the barrel on that rifle came from. That one just wouldn't shoot. Even the throat looked good.
I think if the OP's rifle were mine, I'd get a few pure lead sinkers of the proper size and oil the bore and drive a couple down the barrel, one at a time. Three would be even better and use a good micrometer to determine the groove diameter. It should be .357" to .358". I'd examine the crown for any possible damage and I'd definitely check out the twist rate. If it's slower than 1 in 16" then the barrel needs to be replaced. A 1 in 16" will stabilize bullets up to 250 gr. and sometime, though rarely even stabilize 275 gr. bullets.
Currently I have three rifles in .35 Whelen, a Ruger M77RS, a Remington M700 Classic and a custom Mauser. The Mauser has a 1 in 14" twist and the two commercial rifles have 1 in 16" twists. My next planned custom will have a 1 in 12" twist which if I understand things correctly is what was originally used in the Whelen.
There is something radically wrong with that rifle and my money is on the barrel needing replacement.
Paul B.