1,000fps should shoot with almost pure lead bullets - if the bullets are at least groove diameter & if the alloy matches the pressure being developed.

If they are undersize, smokeless powders won't work worth a damn as they are not fast enough, or hit hard enough to slug the bullet up.

Any alloy harder than pure should work at low velocity - and with the max loading of Trail Boss, the velocity could be up around 1,200fps however - the problem - the pressure will also be up around 30,000PSI, which means you will need Wheel Weight alloy or possibly stronger.
The alloy should match the pressure as that relationship is more important than the speed.