05-24-2021, 10:53 PM
I had a similar issue with a 223AI, but it had a 40-60% failure to fire rate with factory ammo. I used a competent gunsmith and we dissecting the issue, which turned out to be all of the factory ammo was .005" - .014" short of spec at the shoulder so firing pin was lightly hitting the primer and throwing the cartridge further down into the chamber. My solution was buying new LC brass and fire forming from scratch.
You may encounter a similar issue with the excess headspace using the Lapua brass. To reduce the risk of this happening you might consider loading your bullets long (jam into the lands) and use a full charge of powder to quickly seal the neck and push shoulder forward. I would start with a small test batch. If you notice heavy excessive soot on outside of case then you might need to create a false shoulder to help seal the chamber and aid expansion.
You may encounter a similar issue with the excess headspace using the Lapua brass. To reduce the risk of this happening you might consider loading your bullets long (jam into the lands) and use a full charge of powder to quickly seal the neck and push shoulder forward. I would start with a small test batch. If you notice heavy excessive soot on outside of case then you might need to create a false shoulder to help seal the chamber and aid expansion.