Originally Posted by Rem700addict
I've been reloading my .300wm and I've noticed that my cases have been getting a lot of powder residue around the outside of the case neck.
What is the diameter of the neck of a loaded round? What is the diameter of the neck on a fired round, I’m betting around .338”? What is the difference? I have noticed on some of the necks of my fired rounds the greater the difference between the two measurements noted above the more carbon formed on the neck. Hopefully the carbon is only on the neck and not protruding down the shoulder. In my experiences a difference of .006" or more showed the most carbon buildup on the necks and increased as the neck clearance increased. Brass will usually spring back .001" or thereabouts after firing so the total difference in neck clearance will be approximately .001" more than the measured fired neck diameter. Be sure to clean off the carbon when making the measurement. At times the difference in clearance measurements will differ between different manufacturers of brass. Some brands of brass have thicker necks than others.
If you are not over .008" and accuracy is not an issue I wouldn't be too worried. The neck diameter of your chamber will probably be within SAAMI specs.
As far as cleaning the neck area of the chamber, usual sound cleaning methods while cleaning the barrel should serve your purpose.