Originally Posted by
Kestrel
The 3 burst mechanism isn't exactly a true 3 burst mechanism, like the MP5. The ratcheting mechanism inside causes variations in trigger pull that affect accuracy.
I also thought part of the reason was to prevent fouling of the breech since the gas directly impinges on the bolt. I heard the M4 especially is prone to fouling since it's cyclic rate is significantly higher than the M16's.
I was always told never to use 3-shot burst unless providing covering fire. Personally, I couldn't think of any other reason to use it unless you were trying to clear rooms with an M16... Which in any case, would put you at a huge disadvantage anyway, since the buttstock isn't retractable and the barrel is long as hell.