Okay: Not a pro blacksmith here,but as an amateur and rancher most of my life I do know branding irons..
The MOST important thing is that,wherever there is a joint in a letter or symbol,there must be a GAP made or the area will be so hot that the brand will "smear" or burn the hide excessively so it is not a clear brand.I'll try to dig up some old irons and put some pictures here in the next few days to demonstrate. The irons should be tapered with the narrow end of the taper at the bottom of the brand and wide end up.This allows the iron to retain some heat while still doing a clean job.5/16 X 1 1/2 stock is a nice size. Tapered to about 1/4 on bottom. Horses are VERY thin skinned and I use round stock to make my horse irons.Just a QUICK touch on the hide gets the job done.Actually I went to freeze branding my horses about thirty two years ago using the liquid nitrogen from my artificial insemination tank. The area frozen comes back as white hair and is a really pretty brand.
Sorry if I can't describe stuff with words so well..... Again; Pictures soon...