I bought a branding iron through El Toga Freezebrands once, they advertise in Bull Cry.
They sent instructions on how to freeze brand, from start to finish. They seem to work really good and it tells you exactly how long to hold a brand on depending on the breed of dog.
This is just with dry ice and alcohol, stuff easily purchased. But it works just fine.
In my opinion, the most important part of the branding is to make sure the hair is all removed good, and most importantly, make sure the dog is secured and can't move.
That is what has always caused my brands to go screwy is a moving dog where I couldn't hold the iron steady. I had one dog that the Chicago Bears couldn't have held still for 30 seconds. It was pretty impressive to watch 5 grown men trying to hold one 9 month old dog still... and couldn't do it.
I'll pass on the pups, got my hands full as it is. Take care.
-Dawg