Headless...do it with a proper wrench or you'll scratch it all up (I'd probably still scratch it with a proper wrench...but that's just an issue with me
). If you need a hand just pop over later this week. It'll only take a minute.
The RATech Prime spec bolt is (to the best of my measuring) 3.18-3.25mm longer than the G&P spec bolt (at least the one I have which I suspect is G&P). I decided to take just shy (a scribe lines worth) less than 3mm off the rear of the prime bolt. The width of a hacksaw blade + a couple of seconds on the grinder. I left it a hair longer than the G&P spec bolt that I had originally...no ill effects. The RAtech bolt is certainly heavier by quite a bit....I wonder what is going to break next...
The rest of the major outside dimentions of the bolt are the same...the rectangular notch for the plastic rectangular retaining plate for the bolt is bigger on the RATech bolt carrier...so the filler pieces (tried a Airsoft Surgeon, G&P and Element) are a bit loose. Dunno if that's an issue or not.
Anyways...cut/ground it down (approx 15min going slow). Works like a charm.
Rocks in both the SR16 and MUR bodies. Recoils up (by "feel"), ROF is down. Fiddling with the buffers/buffer springs and spacers adjusted the feel nicely. Before the SR16 felt a bit wild (i.e. it's going to bust something wild) and the MUR was mild. Now they're both somewhere in between.
Definitely uses more gas per shot.