There is a lot of 223 data out there but really little on millspeck 5.56 chambered rifles. How much more powder can I use over standard 223 data in my Rock River Arms upper which is set up to use the 5.56 round. It is a 16 inch barrel and I want to match the XM193 round velocities along with working up top loads with heavier bullets. It has a 1 in 9 inch twist.

only way i can think of is to Crony the 556 and load the 223 the same speed.

I never had any problem using 223 data, I think most of it (Sierra, Hodgdon, AA anyway) is geared towards 5.56.

You really sacrifice brass life trying to hit m193 velocities. Work your loads up and when you start to see pressure signs like rim lifts and/or ejector scrapes, back off 1/2gr with ball powders and 1/4gr with stick. Your brass will last forever and nothing you hit with it will be able to tell the difference.

The heaviest bullet will will probably get away with is a 69 Sierra or a 73 Berger.

Here is Sierra's data: Sierra AR Loads

Thanks for the download.