I've found only one brief mention of Form 1 in this thread, so I'm throwing this out there for elaboration: Has anyone successfully done an SBS mod on a 1301? Elsewhere I've seen speculation that it might be possible with just shortening the barrel and without any gas system work, but nobody seems to know for sure. I may be having a spare 1301 barrel come into my possession, and if an SBS conversion is an easy process, I'm going to try it. Thoughts?