I have to ask how to figure out how much powder to use. I would like to see as high velocity as possible and higher pressure for more reliable cycling.

Ever thought about looking in a reloading manual?

I have three that have loads for the T.C. Contender with a 14" barrel.  Try the Hornady, Speer, and Alliant powder manuals.  Alliant is online if you don't want to buy one.

I'm sure there are others.  These are the ones I know, for a fact, have your info.

Kent

Why? My 7.5" cycles just fine with std rifle loads. Yours wont cycle,, FIX IT! Use of pistol powder in a rifle is an accident ready to happen. Here is a pic that was forwarded to me:

Alliant has some published loads with 2400, but the velocity is lower, not higher, than the loads using rifle powders. If you attempt to get high velocity in 223 using pistol powders you might blow yourself to bits

At this time, I would like to nominate m60308nato for an honorary WECSOG* award.  Usually, this is awarded posthumously, but it looks this has not happened yet, but may in the near future.

:)

Seriously, though, there are some reloading data for faster powders such as 2400, but you will find little advantage in using them.  Please, please, do NOT experiment with this kind of stuff.  Use only known data from reloading manuals!  Fast burning pistol powder + .223 case = exploded AR.  I saw what happened once when someone accidentally loaded his .223 cases with Winchester 296.  The upper receiver had to be pried out of the ceiling of the firing line.  Various parts of the lower receiver had to be pried out of the shooter's face.
* WECSOG - Wile E. Coyote School of Gunsmithing

www.quarterbore.com/ar15m16/ar15kaboom.html

Peak pressure in the .223 happens when the bullet is between 4 and 7 inches down the bore depending on bullet/powder combination with normal powders.  You cannot get a higher pressure safley with a faster powder so don't even try it.  Only one range of powders works for a given cartridge.  Barrel length does not change powder requirements.

Man, I wish I had a nickel for every time I have heard someone think that just because they are shooting a "Pistol", that you should use pistol powders.  I've loaded rifle calibers in pistols for a lot of years now, and let's make this plain and simple.  If it is NOT IN A MANUAL, DO NOT LOAD IT!!!   That simple.
 A real good rule of thumb to use is if you do not have or have access to a reloading manual, don't reload.  If you don't see it listed, don't use it.  Keeps you hide intact and the hide of those around you.  

You know what they say, make something idiot proof and they will come up with a better idiot.