Here's an interesting conversion which almost works. Just playing around in the reloading room and found that the base of a .223/5.56 case is pretty much the same as a .380 ACP base. I cut a few .223 cases down, trimmed them to .380 ACP length and ran them through a FL resizer. Well it almost works except the case wall of the converted brass is around 20 thousands thick at the neck which caused all types of chambering problems with the dummy rounds I put together. Didn't measure the volumn of the converted cases but I'll bet they are a lot smaller than true .380 ACP cases. Oh well, maybe they will be good for shot shell development.