Rem. 700 .223 feed rails

[MarcH]

Have a Rem 700, origionally in .221 Fireball. Have re-barrelled to 20 Practical,.223 necked to .20 cal.). Have replaced the magazine box, follower spring and follower. Won't feed properly. Pretty sure its the feed rails. Right now the feed rails are opened up for only about .500 just behind the ramp leading to the chamber. I'm thinking the feed rails on a .223 are opened up for a greater length. Anyone have a 700 willing to measure the length the feed rails are opened up just behind the ramp leading to the chamber?
Thanks