A rare gun. Here's what I have on it from the references I'm working on right now (yea, still revising...but hope to have them out shortly!!).
MK678GC (Ruger model 0178). Special Distributor model. A total of 991 shipped in 1996 to Go Sportsmen (MN) – known s/n range 218-62413 to 218-69307 and an additional 739 shipped from 2002 to 2003 to BIG ROCK SPORTS distributors (Henry's (NC), CSI (MN) and MT Sports (MT) – s/n's unknown but should be with a 225- prefix. A total of 1,730 produced from 1996 to 2003).
Send me a PM if your SN falls outside of the listed range. Am especially interested in getting any notes on that later run of guns.