Post pics of the bolt head.
This is not exactly correct.Link to one of many previous discussion: http://www.hkpro.com/forum/hk-nfa-talk/116914-what-do-i-have-action-3-f-modified-bolt-head.html
The Action 3 will have a cut out or depression in the face, the older style is flat (see photos in above thread).
The slot in the top of the bolt head (above the rollers) is narrower for the spring and the old style plate will not fit (but the newest F plate may, per Shattered ... hum wonder if have a F bolt head there?) While many of the guys have used the spring retainer instead of the plate, have seen where the spring shifted, wore through, fractured and damaged the inside of the bolt head ... in less than a case of ammo. So we tend to use what ever retainer the bolt was designed for (when the guys are shooting subgun matches get to see a lot of ammo go down range and lots of failures of firearms ;-)
The "wide" plate slot exists on the old style non scalped bolt faces. Thus had assumed (in correctly it appears) that there was a progression of wide to narrow slot. However, if I have it correct this time, the narrow slotted scalped bolt face bolt head is the Action 3 and the wide slotted scalped bolt fact bolt head it a F type?This is not exactly correct.
The wider plate-style roller holder was designed for and first used in the "F" (French) model MP5 bolt head. It WAS NOT used in the original "Action 3" bolt head which came years before the F model. Both have the Action 3 bolt face scallops but only the F version has the larger (wider) plate roller holder. The Dynamit Nobel/Geco Action 3 ammo with unique ogive favored by German police required some help in feeding thus the face scallops. These special cuts were retained in the F model bolt head as they do not adversely effect feeding of other types of 9mm ammo and the stronger roller plate, added to deal with high pressure ammo that the French police wanted to shoot in their MP5's, do seem to hold up better, sometimes. The F model plates still break depending on the ammo used, firing rate and other factors. This still remains like the extractor spring design the weakest point on the MP5 and other HK roller-locked weapons.
Wise owners have spares.
so I finally found the parts in question, I guess the one pic should tell it. not action 3 or F, no scallops on the face.Post pics of the bolt head.