I load for a couple Handis, and use FL dies. These things can have some tricky chambers and throats.
Easiest way is to have the barrel off the frame, hopefully it's an Extractor type.
The idea is too size the case enough to fit into the barrel/chamber so the head is just flush with the end of the barrel/breach. That's all we can do with the single break actions,, sometimes the shoulder is the limiting factor,, sometimes it's the body,, either way it can be done with the FL die.
Run the Ram up and turn the die down to contact the shell holder, now back off a full turn. Size a case and try fitting it into the chamber, won't fit flush will it?
Slowly turn the die down in little 1/4-1/8 turns and size again,, try the fit again,, repeat,,
I actually use a feeler gauge between the bottom of the die and the shell holder once I find the sweet spot. An example is my 308, the space between the die an shell holder is .003 for my FL die too make the case fit just flush in the chamber and getting there is alot less than a 1/8 turn from won't fit too fit.
(that's with my die, my press and my chamber,,others milage may vary)
If it's an ejector type you'll have to figure out some way to clamp the ejector down and in so it's not contacting the case head. (just clamping it in can still leave the ejector too high rubbing on the case)
As mentioned, hitting the FAQS on the NEF forum is priceless, check out barrel fit issues, if theres even a small gap at the head/breach area sizing variables can help make the proper fit.
I've found the biggest issue aiding accuracy with the Handi is concentricity, being sure everything with the case/bullet is straight and runout is a minimum.