This question comes back every so often. I decided to try collecting list of trigger groups that work with HK firing pin safety, so can be used either in lower other than HK or dropped into HK lower. Looks like most M16/M4 select fire triggers work with it, so list is of semi-auto triggers. Please take in mind that HK firing pin safety takes some hammer energy to disengage. Using very light trigger setup with light hammer springs can lead to light primer strikers on some brands of ammo (surplus, Russian, etc.):
ALG Defense ACT
Armalite National Match 2-stage
ATC AR-Gold Trigger (needs fitting for MR223 due to rear receiver pin location)
CMMG Gen2 2-stage
Franklin Armory Binary Firing System III (BFS III)
JP Competition Trigger
JP EZ Trigger
Geisselle HK MR556
KAC 2-stage
RRA National Match 2-stage (CAUTION: Only new version with rounded hammer is compatible)
TAC-CON 3MR
Timney AR-15 Skeletonized
UHL Trigger (German made)
Wilson Combat TTU-3G and TTU-M2
I will try to update this list when new info will come in. Please give confirmed info on other triggers, I will update list.
WARNING: Some triggers will not work properly with HK safety from 2-stage "European" trigger (one that allows to be put on safe with hammer down). Old style HK safety or aftermarket safety may be necessary.
Remarks:
Geisselle SSF - standard model reported not to work reliably with HK416, special model required.
Last update 27th of Dec 2017 (BSF III added)
HK P2000SK in 9x19mm with 6lb LEM trigger. I added also HK45C magazine release. This is huge improvement over standard magazine release. I have Meprolight night sights, that soon will be changed for new ones - tritium inserts are coming to their end. Magazines are equipped with Pearce Grip PG-2733 extensions. Those are intended for Glock 27 and 33, but modified work fine with P2000SK. They give much better grip on pistol, without adding much to size and +1 capacity. Most of the time pistol is equipped with Viridian C5L green laser and light combo. I think C5L is perfect package for subcompact gun. Only if Viridian come with more reassuring mounting solution. All this stuff sits nice in Raven Phantom holster and magazine pouch. Holster is configured for OWB carry, but I also configure it for IWB and even AIWB. I do shoot it sometimes in IDPA SSP (with C5L removed) and in 3Gun Liga Sportera. My trusty P2000SK is now oldest in my inventory and it never let me down. I totally trust this little beast.
