Too much freebore, and not enough room in the magazine for Cartridge Over all length.
The above was said previously, deserves repeating for those not into safe queens.
Gunsmiths may BS you on how good the barrels shoot with their reamer, but remember, if you can't kiss the lands, then find pressure, you screwed from the get go.
I learned the hard way to get a gunsmith to run the reamer in to the depth of the shoulder on the end of a barrel stubb and mail that to me. If he takes a quarter cut on a milling machine you will have a "window" to see the lands and freebore. You can still insert a case with a bullet in it to check the exact amount of freebore and OAL as the rifle will come to you with a new chamber.
The above is where you start if you want a super accurate rifle, but it is usually just a passing question or no interest in it at all.
