Question on measuring bore diameter/slugging the bore

[usmc0811]

I have slugged the bore on a few of my semi pistol barrels and this was my process.

1- I removed the barrel to be slugged
2- I took an empty case for the proper caliber needing to be slugged and filled with molten lead then let cool.
3- Removed the "slug" from the cse using a kinetic puller.
4- Using a wooden dowel and rubber mallet forced the slug through the muzzle end all the way out to the other side.

Now so far I feel good with what I have done but then I alway get confused as to how to properly measure the slug. Do I
measure the parts on the slug that are HIGH spots that would be the groves of the bore, or the LOW spots on the slug that
would be the lands in the bore????
Now if my cast bullets are dropping from the mold to the exact same size of the bore or slightly larger say .001''-.002''
bigger than no need to resize, correct??

Also if doing a revolver doi slug the barrel, the cylinder or the forcing cone part off the barrel? Am I just thinking to much into this LOL thanks guys Alway appreciate you help and feedback.

[mdi]

The high spots are the groove diameter of the barrel. That is the dimension most used to determine a good bullet diameter. The "bore" will be the small diameter of the barrel (the barrel ID prior to cutting the rifling), and the bullets only the same size to .002" larger than the bore will probably cause problems (leading, keyholing, accuracy). For my semi-auto pistols and rifles I shoot for bullets .002"-.003" over groove diameter as a starting point. For my revolvers I slug the barrel for information, to make sure the groove diameter is smaller than the cylinder throats. For my revolver bullets I measure (slug, pin/plug gauge or expanding ball gauges) and size my bullets to the same OD as the throats' ID. This is also a good starting point and more often than not, works quite well. If a bullet is larger than throat diameter it will be swaged down to the throat ID as it passes through when fired. For bullets smaller than throat diameter, leading and poor accuracy often occur.

I use slugging methods similar to yours except, I use a mallet and a brass rod. Using a wooden dowel there is a possibility of the dowel breaking, splitting and jamming in the barrel. I've read about that happening a few times here on castboolits. And I prefer the "tap, tap, tap" of a harder mallet to the "push" of a rubber hammer but that probably is just my shop methods, preferences (lifelong machinist/mechanic). https://www.mcmaster.com/brass-rods

One major plus of measuring your guns for cast bullet use is the knowledge gained. You know more about your guns...

A bunch of good reading for a self quarantined day; http://www.lasc.us/castbulletnotes.htm

[usmc0811]

Thank you for clearing it up for me. You helped me big time. I will have to get myself a brass rod and mallet.

[ioon44]

I have used a steel rod wrapped with masking tape to protect the barrel.

[Der Gebirgsjager]

Better to slug from the breech end when possible.