Mouth to chamber distance

[uhjohnson]

I am working up a load for an unknown rechambered straight walled 1867 Werndl carbine using modified 45/70 brass with a .452 cast and when inserting into the chamber it slides in freely, with a 3/16 wide single layer of .0015 cellophane tape around the mouth it sill goes in freely, with 2 layers it stops about 3/16 from going in all the way. How much case/chamber clearance do I need for a bullet to exit without undue restriction and at this point should I consider reducing the the neck wall thickness
I have done a chamber cast and slugged the bore

[country gent]

l navs a cluple tight neck chambered rifles that I use with .0005-.0007 clearance on the loaded round dia. They are set up this way a factory round in the 243 wont chamber. .267 neck tun lapua brass to .2665 -.2663 very accurate course rifle. Also used it for 1000yds.

You need enough clearance so the case can open to release the bullet figure .001 min so your probably good.
I would recommend measuring the taped case as accurately as possible then measure the first few loaded rounds. Neck dia will change when a bullet is seated as neck tension on the bullet swells it a little. A chamber cast might not be a bad idea either.