Is this a trick question? What you are asking for is the .20 PPC USA but improved. There is no reason to improve this case, the volume is so low that to improve this case solves virtually nothing since the case is very efficient as is.
If you truly need a starting point based on using .220 Russian brass then you can start at 29.0 grains of V V N140 with a 36 grain Berger HP and an OAL of 2.000" to 2.005".
You can also check on the .20 Tactical and the .20 Vartag.
Thank you The 20 x 39IMP is listed in the COMPETITOR PISTOL. I would like to know more about the 20 Tactical is this the 20 x 223. Who has dies for this caliber and loading data.Right now I have a 22 Hornet with a 14" bbl and I love it for varmint hunting. I all so have a 375 JRS Mag bbl for this gun. I use a Contender in 221 fireball too
Paul, A good place for you to start would be www.smallcaliber.com This is an excellent site for subcaliber catridges and news about them. Yes the .20 Tactical is a .20 cal. on the .223 case. Bill Check out the small caliber section here and look for a thread titled "20 Tactical".
[This message has been edited by Bill Tompkins (edited 07-13-2001).]