May I inquire as to what you're reloading ?. Powder.bullet ,charge . When You state it won't chamber ,why is that , Casing isn't properly resized ?, OAL is wrong ? . Need details to correct the problem .
The .223 Wylde chamber. The chamber is made with the external dimensions and
leade angle found in the military 5.56×45mm NATO cartridge and the 0.2240 in (5.69 mm)
freebore diameter found in the civilian
SAAMI.
The .223 Wylde chamber is used by rifle manufacturers who sell "National Match" configuration AR-15 rifles, barrels and upper receivers.
https://en.wikipedia.org/wiki/.223_Wylde_chamber