Currently working on the Modelo Polylactico and was wondering if anyone else had a good solution for sanding the longer Intermediate shells. I had no issues using a 6mm drill bit + painters tape shim as a mandrel for the Beginner 209 shells, but the Intermediates don’t have enough surface area or depth due to their smaller holes to stay on the other smaller drill bits I’ve tried. I suppose I could force/tap an M2 or M3 screw into the top powder hole but would widening the hole cause issues if its sealed well?
I also noticed that the shell models had inconsistent rim thicknesses in Orca.
- Headspace gauge/jig rim: 1.8mm thick
- Intermediate .355 rim: 1.6mm thick
- Beginner 209 slug and shotshell rims: 1.2mm thick
Obviously there would be an issue if the 1.2mm rims were used to headspace, preventing the thicker shells from loading, but wouldn’t too much headspace also cause trouble like light strikes and case bulge/FTEs?
So, you seem like you are in the right track.
Use a 1/4" drill bit as a mandrel to hold the beginner shells for sanding.
For intermediate (or any upcoming load that uses small primers) you use a T25 Torx bit as the mandrel. I recommend a new one with crisp edges. You can also use the torx bit after smoothing the cases to ream out the primer pocket to size.
The beginner loads use a 209 primer. The 209 primers protrude out the back of the case because of the incorporated rim/flange. This makes up for the difference in headspace.
The headspace gauge is .2mm thicker than the shells (or beginner rim+209 flange thickness). This build with 43r Ammo is very forgiving with headspace. If you accidently used a beginner shell to headspace, you can just file some off of the breech end of the barrel, and file the extractor groove a little deeper. If you mess up and have too much headspace, you can sand some off of the front of the receiver to make up for it.