M4 RIS Threading problem

[Jbone 11 11]

I currently have a Royal M4 CQB with a after market metal body (might be G&G... or JG not sure). I wanted to swap out my current RIS handguard, which has that spring loaded ring (where the receiver meets the barrel) to hold the actual hand guards in place (is that an m733 style?)
See first pic:

The one I want to swap in is the type that has a screw on ring like in the second pic and is used. My problem is, when I unscrewed the (original) spring loaded ring from the receiver body, the other one didnt seem to match the threads on my receiver body. At first I thought it was just being a pain in the arse (as the old one took some elbow grease to come off), but it just wont go past the first couple of threads.

Is it common for the threads to differentiate between these two types of handguard mounts?

Cheers,
J

[ILLusion]

The spring loaded one you're referring to is the standard delta ring. These are used for hand guards that can be split in to two halves - this is a requirement if you have any intention of mounting an M203. It is not M733 style. Almost any M4, M16, Knight's, Colt, Armalite, etc etc still use that same spring loaded delta ring and barrel nut system.

The "new one" you're referring to is the type of ring used for free floating handguards and is designed by Knight's Armament Company. These types of handguards are solid pieces and can not be separated. Installation is also a bit more difficult, but accuracy of the setup is higher, as any pressure applied to the hand guard does not affect the barrel in any way.

What brand barrel nut are you using and what brand metal body? There is no industry standard... some use Imperial threading like real steel, whereas others use Metric.

[Jbone 11 11]

Thanks for the info! I've been getting a bit confused as to what is compatible with what as far as the front end goes! Im guessing my issue is exactly what you have mentioned, Imperial vs. Metric
upon further inspection, it seems the ring for the free floating hand guard is "just" slightly smaller than the male end on my receiver. As for the make, I got it second hand from a mate, but on looking at similar products online, I believe it to be a Dboys M16 Forend conversion kit. All the parts match up at least.
As for the main body, I think its eiter G&G or JG.... sorry for the ambiguity, but I live in Italy and don't have that good a handle on Italian just yet... : /
Again... thanks for the info. Any way of finding out in advance whether parts are Imperial or Metric?
J