The Action 3 has a relief cut milled in the bolt face for better feeding, which in my MP5A2 helps when shooting suppressed. The F series has an improved firing pin system, which the inside of the bolt is milled for (so the story goes), improved roller retainer spring , a reduced diameter on the bolt carrier neck and changes in the recoil spring retainer and bolt carrier recoil spring mounting hole (larger?).
Some where along the line from Action 3 to F Type the roller retainer was changed from a plate to a wire and in turn the slot in the bolt head was made narrower (have to check, have an Action 3 / F type of both type roller retainers). A lot of the guys use the wire retainer in the wider slot bolt heads that had the plates, however, seen on case where in a few thousand rounds the wire wore through due to shifting, thus best to use what the bolt was made for.
One of the threads below discuses the necked down carrier now being included in new Action 3 carriers (or should I say was with the current non supply issues of German parts). Good luck and looks like need a new book (on line or off) with all the variations of MP5s
http://www.hkpro.com/forum/hk-nfa-talk/128478-action-3-bolt-face.html
http://www.hkpro.com/forum/hk-rookie-corner/102341-action-3-wire-roller-holder.html
http://www.hkpro.com/forum/hk-talk/100099-action-3-bolt-carrier.html
http://www.hkpro.com/forum/hk-talk/120002-mp5-bolts-3-fs-1-a.html
http://www.hkpro.com/forum/hk-nfa-talk/130093-mp5-full-auto-bolt-group-question.html
http://www.hkpro.com/forum/hk-clone-talk/98412-mp5-carrier.html
Some where along the line from Action 3 to F Type the roller retainer was changed from a plate to a wire and in turn the slot in the bolt head was made narrower (have to check, have an Action 3 / F type of both type roller retainers). A lot of the guys use the wire retainer in the wider slot bolt heads that had the plates, however, seen on case where in a few thousand rounds the wire wore through due to shifting, thus best to use what the bolt was made for.
One of the threads below discuses the necked down carrier now being included in new Action 3 carriers (or should I say was with the current non supply issues of German parts). Good luck and looks like need a new book (on line or off) with all the variations of MP5s
http://www.hkpro.com/forum/hk-nfa-talk/128478-action-3-bolt-face.html
http://www.hkpro.com/forum/hk-rookie-corner/102341-action-3-wire-roller-holder.html
http://www.hkpro.com/forum/hk-talk/100099-action-3-bolt-carrier.html
http://www.hkpro.com/forum/hk-talk/120002-mp5-bolts-3-fs-1-a.html
http://www.hkpro.com/forum/hk-nfa-talk/130093-mp5-full-auto-bolt-group-question.html
http://www.hkpro.com/forum/hk-clone-talk/98412-mp5-carrier.html
