There have already been a ton of posts that cover this subject well.
I'd like to add my recent experience. I bought a horse last year - 9
yr old gelding who had never been shod in his life. Barefoot, he
never interfered at all. With the first pair of shoes, he forged (as
your horse is doing), and clipped himself on both front cannon bones.
His angles hadn't changed. No problems with symmetry. Our only
conclusion was that he was "close" previously, and the weight of the
shoes exaggerated his movement to cause the interference.
It took us 4 sets before we had reasonable control over the
interference. To this day, we have to be careful with his shoeing
or the problems return. We have an excellent farrier who rides
endurance himself - nothing is too good for him if it keeps him
coming back to shoe our horses with his endurance experience. When
we say we have a heavy schedule ahead of us with a lot of miles on
the road, he KNOWS we mean RIDING in rough terrain. He understands
that we wear out shoes between sets! (One farrier told me to stop
riding down the blacktop & I'd get better wear on the shoes. We were
riding on clay roads!)
Good luck with the shoeing. We're great believers in small changes
to allow the horse to adapt & show us how close to "right" we are.
Linda Flemmer
ABF Challenger ("Rocket") & Eternal Point ("Major")
Blue Wolf Ranch Chesapeake, Virginia, USA
"In case of emergency - Fur side up, steel side down!"