Maximum CBTO in my rifle
 

It’s super common to have magazine box length be shorter than the chamber length to the lands. Most of us simply choose a bullet which tolerates jump and load to magazine length. The other option within that barrel is to port drop your rounds and single feed - turning the rifle, functionally, into a single shot. A third option MAY be to convert to a longer mag box, or DBM which offers a greater COAL tolerance. The fourth option you have would be to rebarrel the rifle, or have your barrel set back and rechambered to shorten your chamber length to match your mag box length with your desired bullets.

what chambering? some cartridges are designed to have freebore in the chamber to give higher velocity without excessive pressure.