  Here we show that addition of Hf to Nb4Ta can significantly improve the high
field performance of Nb$_{3}$Sn, making it suitable for dipole magnets for
Future Circular Collider (FCC). A big challenge for the FCC is that a realistic
production target for FCC Nb3Sn requires ~30% improvement over current
conductor performance. Recent success with internal oxidation(IO) of Nb-Zr
precursor has shown significant improvement in the layer J$_{c}$ of Nb$_{3}$Sn
wires, albeit the complication of providing an internal O$_{2}$ diffusion path
and avoiding degradation of irreversibility field($_{irr}$). We compare Zr and
Hf additions to the standard Nb4Ta alloy of maximum H$_{c2}$ and H$_{irr}$.
Nb4Ta rods with 1Zr or 1Hf were made into monofilament wires with and without
SnO$_{2}$ and their properties measured over the entire superconducting range
up to 31 T. We found that group IV alloying of Nb4Ta raises H$_{irr}$, though
adding O$_{2}$ still degrades this slightly. As noted in Nb1Zr studies, the
pinning force density F$_{p}$ is strongly enhanced and its peak value shifted
to higher field by IO. A surprising result of this work is that we found better
properties in Nb4Ta1Hf without SnO$_{2}$, F$_{pmax}$ achieving 2.35 times that
of the standard Nb4Ta alloy, while the oxidized Nb4Ta1Zr alloy achieved 1.54
times that of the Nb4Ta alloy. The highest layer J$_{c}$ (16 T, 4.2 K) of 3700
A/mm$^{2}$ was found in the SnO$_{2}$-free wire made with Nb4Ta1Hf alloy. Using
a standard A15 cross-section fraction of 60% for modern PIT and RRP wires, we
estimated that a non-Cu J$_{c}$ of 2200 A/mm$^{2}$ is obtainable in modern
conductors, well above the 1500A/mm$^{2}$ FCC specification. Moreover, the best
properties were obtained without SnO$_{2}$, the Nb4Ta1Hf alloy appears to open
a straightforward route to enhanced properties in Nb$_{3}$Sn wires.
