You need to find a reloading book that will list the components and powder you are using. If your charge weight is near max or if you are picking a charge that someone has used on the internet, reduce by at least 10% and work up, looking for overpressure signs. On using internet, or hearsay loads, I like to get a few corroborations so I can see if the load is in a safe pressure area.
If you are loading for a gas gun, pay particular attention to the max trim length, COAL(cartridge overall length), primers are seated below flush in the case, and shoulder bump. You want the case to slip into the chamber easily to avoid slamfires.
If you are near max, and you are over 1 grain, you might be overpressure, if you are near minimum and under 1 grain you could have a squib(bullet stuck in the barrel) which would be a bad day, if you were to try and fire another round.
Alliant Powder has a reloader's guide with a few components and recommended charges. I didn't see anything with 62 grn fmj... Maybe you can play around somewhere in the range of the 69 grn load areas...
http://www.alliantpowder.com/reloaders/RecipeList.aspx?gtypeid=2Here is a good article on reloading for gas guns and service rifles, from Sierra...
http://www.exteriorballistics.com/reloadbasics/gasgunreload.cfmAs always, I will tout the OCW method of load development, for finding the most tolerant and consistent charge weight for rifle.
http://optimalchargeweight.embarqspace.com/I do not load .223, but I know that there are some guys on this site that use RL15 to load for .223, hopefully they chime in. Maybe add ".223 and RL15" to your thread title.