Run the Gorx 3f, try some Swiss if that doesn't work out.
I've had success with 1-1/2F Swiss where I couldn't get Goex to work.

It's possible you have a rifle that won't shoot with big charges.
Make double damn sure that the wood-metal fit is dead-on at the breech.
If the metal's banging around in there you don't stand a chance.

Cheers
Tinker