What has to be done to a ambi trigger group for it to work on a MP5 RR? I know it has to be a clipped and pinned housing but is that it? Thanks jm

Not sure I understand.....

as 'most' registered receiver MP5s use 2-push-pin ie, swing-down lowers.

I must have it wrong then. I thought that there was some rr MP5's without the hole drilled completly through. My question was do you still have to modify the trigger pack?

Quoted: Not sure I understand..... as 'most' registered receiver MP5s use 2-push-pin ie, swing-down lowers.

Most RR's use push-pin lowers.  Some don't.  You can read more about that HERE

Read on HKpro to figure the diff.
RR will have push-pins
Sounds like someone has a "registered sear"
Thus you need to C&P the pack and modify the front metal of the pack to sit on the 'shelf'

Atleast that's the way I understand it. Very well could be wrong.

Maybe he's talking about one like this: www.ar15.com/forums/topic.html?b=7&f=118&t=418708

That's kinda what I was thinking.

Nail on the head

Quoted: Maybe he's talking about one like this: www.ar15.com/forums/topic.html?b=7&f=118&t=418708

Quoted: Not sure I understand..... as 'most' registered receiver MP5s use 2-push-pin ie, swing-down lowers.

You've got it totally backwards; most RR MP5s are clip on lowers and swing-down lowers are the rare ones.

A clip on lower RR can have the packed modified to an extent to take other trigger groups configurations.

Originally Posted By Hail Mary: You've got it totally backwards; most RR MP5s are clip on lowers and swing-down lowers are the rare ones.

Absolutely correct.  There are MANY more clip-on RRs than push-pins, that's why Push-Pin RRs will fetch 3-4 thousand dollars more than Clip-On's.

Back in the days when individuals could Form 1 a machine gun, very few C2s were converting HK receivers by drilling the push-pin hole, eventhough it was far easier to do, because there was almost no source for factory MG lowers.  C2s usually had to extensively modify the semi-auto trigger pack with a home-made sear in order to make it all work, then registering the whole gun, hence creating a Clip-On RR conversion.

Only when a C2 or individual could get their hands on a factory MG lower would they convert the semi receiver by drilling and this is why there are so few of them around.

Its my understanding that RR mp5s are bacialy non -existant, and most were done by flemming and had the sear pack modified?

Fleming did a lot of RR's but not by any means all of them.  The Push-Pin RRs had no other modifications, just the hole drilled, so they can use a factory MG lower.  They are identical to factory MP5s, that's whay they are so valuable.