I don't remember if the bolt locked back with a single round, unfortunately.
So to summarize this thread:
- Go to a gunsmith, but also don't and try to figure it out yourself
- Headspace shouldn't be a problem so you shouldn't need to check it, but also can be problem, so definitely check it
- A carbine gas system with rifle buffer might be a problem, but also shouldn't be a problem
- Contact the manufacturer
- Buy a new bolt
- Fix the probably wonky gas system
I know in the end I have to make my own damned decisions, and appreciate all the opinions. I just find it funny how contradictory they can be. I was hoping someone could say this thing were safe to test fire, but no one can actually tell me that, and I shouldn't trust the opinions of random people on the Internet for safety.
Side note on Clymer headspace gauges: their .223 and 5.56 NOGO gauges are different! I don't think they should be, but they are. 5.56 is 1.4696, whereas .223 is 1.4666. For NATO gauges Forster seems to only offer the GO and MAX (which I take as field gauge) these days.
I've decided that I probably should:
- Finish my build finally, and register the damn thing
- Get a field gauge, and make sure it doesn't close on that
- Work on the cycling problem
- Find a gunsmith if I can't figure it out
Thanks for everyone's time!