I haven't fire lapped a Handi, yet. I'm still on the fence, working on seeing if my daughter's 7mm-08 will shoot well without it.
You might want to pose your question to Verl Smith of LBT (board sponsor) over in the Cast Bullets forum. I've used his method and materials on three SA Rugers, an M-77 .308, a Model 7 in 7mm-08 and two Marlin .45 leverguns with microgroove rifling, all to good effect. The instructions included with Verl's materials are good enough to do the job, but the Beartooth Bullets Technical Guide has a much more thorough treatise on the subject. I used some of Beartooth's lapping bullets when LBT was out of operation for a few years. Back in July 1993 Ross Seyfried had an article in Guns & Ammo about fire lapping. I have that edition open on my desk now. It's what got me interested and started in fire lapping.
Look in the left frame for "Book"
http://www.beartoothbullets.com/bulletselect/index.htmPersonally, I would never use jacketed bullets for fire lapping. According to everything I've read, slightly oversize, 12-15 BHN cast bullets charged with the proper lapping compound will cut evenly on the top of the lands and down in the grooves. Jacket bullets will mostly ride the lands and will spring back to original diameter after passing through a constriction.
Be aware, there are those who scoff loudly at the concept claiming accelerated throat erosion, etc. I'm not a bench rest shooter an am quite happy with the results.