I use the width method. And it goes like this.
1. Pick a helmet you like (you've already chosen the Recon) and have a good look at the helmet face to face. The widest part of the helm will be the total width, this will vary from helm to helm. For the recon it is around the temples.
2. Take a ruff guess as to how far the widest part is away from the side of the visor. For the recon it is about 1 inch on each side.
3. Now the fun part, measuring your head. Take a peace of paper and tape it to the wall at head height. Stand with your back to the paper and place a mark with a pencil over both ears. Between the two marks is the width of your head.
4. Add 3 inches to that base number for padding. EX if your base number is 8 inches add 3 inches which brings it up to 11 inches. KEEP this number it will be the base for every helm you make.
5. Add the additional width you determined in step 2 to the base number. For the recon it was 1 inch per side so an additional 2 inches. Which would make it 13 inch.
6. Convert that number to mm and plug it into the width measurement in pep designer and the rest will adjust accordingly.
7. Build and enjoy.
I've used this method many times once you have that base number with padding it's just a matter of adjusting it for what ever helmet you are building.
If you need any more help or have any questions about this method let me know I'd be glad to help
