45acp chamber size?

What size should the chamber be? My RO seems to have a smaller diameter than my Bear wad gun.  It appears to be quite a bit different. The RO also shoots a tighter 50yd group.

http://www.saami.org/specifications_and_information/index.cfm?page=CC    Ammo and chamber measurements.  Note there is listed a 45 auto and 45 auto match listing.

Many variables contribute to 50 yd group size. Chamber is important but in scope of things I feel that it contributes less to accuracy than poorly fit barrel would. I have seen Baer pistols with excessive headspace which can throw a wrench in the gears. 
Jon

Baer= .480-.486
RO=   .478-.480
 .005 seems like a lot when your wiggling the bullet around in the barrel.
What do you think? I bought the gun used and it was shot quite a bit, can the barrel be worn out? Will Baer warranty this? The frame to slide fit is not perfect but pretty darn good.

The best groups with different good/proven ammo was around 4''.

Sorry posted in haste, the base dimensions are good but the neck numbers are off, I wasn't all the way to the bottom. Ya.. I have heard that before.