You probably have all this figured out by now but here\’s my thoughts. Remove the barrel first. To check the correct OAL any gun needs I use a Dremel to make a slice about 3/4 down the side of the case in question, remove any burs and insert a bullet and push it into the chamber. when the case gets even with the barrel hood the bullet is seated at the rifling. Carefully remove the cartridge and measure the OAL. Do this a few times to get consistent measurements and then seat your bullets a little shorter. It should produce a perfect plunk test.