A 605 build is next on my list. I am going to use a 20" barrel, have it cut down to 16", and have the gas port opened up just a bit (.100-.110). I plan on buying one of the M16 parts kits from SG since it has most all of the part I will need. I will need to find a slickside upper and order a NDS-XM16E1 lower. I figure that it will be about July or August before I will be able to finish it. It could be earlier if Mike and Harlan can get me a lower sooner than 9 months from date of order. If anyone has a line on a slickside upper, let me know. I will need a XM Grey flat handguard retaining ring too.