When you start reloading use AA #9 powder is extremely easy to work with and you cannot put enough of it into a 10mm case to create pressures that are unsafe but always use safe reloading practices anyway.
Then move up to Blue Dot this powder is will give some of the best high velocity loads you can come up with and once again is easy to work with, last go to IMR800X this is the powder that Double Tap Ammo in the States started with in his 10mm loads until he had propriety powder made up to his specs.
IMR800X will give you the very top velocities that you can achieve by yourself, I have been able to safely push 135gr JHP's to 1850fps from a 6" barreled Colt Delta Elite using it.
It is hard to work with and when approaching top loads must be weighed individually, the tiniest amount to much can push pressures way to high basically only use this powder after you have a fair amount of practice reloading.
I have been loading for the 10mm since 1988 and have tried almost every load combo you can think of I am still using some of my original brass but it is set aside for it's last loading and I will not use it again.
Haven't a clue how many loads I have with this brass lost count a long time ago...
Have 2 KKM barrels for my G20 both are factory length and are chambered in 40S&W and 10mm I also have a Advantage Arms 22LR conversion kit for my G20 I imported it myself legally when we were still allowed to do it.
