I shoot a Savage muzzleloader.
Among us Savage guys, the 300 XTP is one of the great all-time bullets. Great expansion.
Now, we are getting a lot more fps with the smokeless than you are getting with 100 grains of 777.
In fact, the problem we have with the Savage on many bullets, is too much expansion, due to the hyper-speeds we push these bullets.
I would suggest to you that you stick with the regular 300 XTP.
In fact, you would do real well with the 250 XTP with 100 gr of 777.
What I am saying is, if you use the 300, use the regular 300XTP. We are not getting good expansion with our Savages with the 300XTP mag, and at your slower velocities, you won't either.
I really think you would be happy with the regular 250 XTP.