This also came from HK Pro. What a cool web site!
The ONLY LEGAL WAY to install a newer style “Ambidextrous” or “2-shot/3-shot Burst”
style trigger group is if the original, registered or unregistered, conversion sear (or “catch”) can
be mated to function in the “Ambidextrous” or “Burst” trigger pack mechanics. This means you must
discard the factory “sear (‘catch’)” that came in the new pack and affect installation of the original
registered or unregistered conversion “sear” that was utilized in the original fire-control pack. Some
few proprietary “sear” designs can be adapted to fit and made to properly function, most can’t.
As detailed earlier, the conversion pack frame itself has to have been altered to fit the clip-on
semi-auto receiver, while having the new style plastic housing adapted to fit the clip-on receiver, and
then “blocked” to prevent re-installation of an original select-fire trigger pack. Now often enough this
is done with the newer style plastic S-E-F housings which are essentially identical in function to the
older style metal S-E-F versions, and this poses no legal problems by doing so. Because most of the
“direct replacement” style conversion sears are modeled after the friction sear found in the factory
original metal or plastic housing style S-E-F trigger groups, adapting just the plastic housing presents
no mechanical problems.
The legal and mechanical problems arise when we are trying to adapt a newer style
“Ambidextrous” or “2-shot/3-shot Burst” style trigger group. And there is a very good reason not to
simply go ahead and have such an adaptation performed by simply discarding the originally installed
conversion pack and clipping on a newly adapted one. The mechanics of the Ambidextrous or burst
trigger groups are VERY different than the standard S-E-F type of fire control pack, with many of the
component parts totally redesigned to properly function with the burst counter clockwork mechanism
installed. Ambidextrous style trigger groups only offering selective, but not burst, fire modes are also
arranged identically and so suffer this same problem. H&K GmbH actually offered two very distinct
styles of “burst” mechanisms. The first version externally resembled the S-E-F type of housing and
located the burst clockwork mechanism in the rear lower portion of the pack frame. This is
significant as it left the front ‘catch’ position identical to the S-E-F fire control pack!! This means that
this style burst pack, and only this style, can be readily adapted to function with those conversion
sears resembling externally the factory friction catch!! These very rare fire control packs command an
extreme premium in today’s market as they can be easily adapted to function with the most common
versions of conversion sears, and the market for using them to install registered conversion sears
primarily, is very strong. The second style of burst pack located the clockwork mechanism more
toward the frontal region of the pack frame and this forced a complete redesign of the internal
components. These new style burst packs cannot be easily or readily converted to use a NFA
conversion sear!! Many styles of proprietary NFA conversion sears simply cannot be adapted to
function without major mechanical redesign. Due to this fact, there is a large temptation to avert the
hassles in doing so by simply adapting the entire trigger group and exchanging it on a “Registered
Receiver” guns’ receiver that formerly used an unregistered conversion sear. Attempting to do so
leaves one extremely vulnerable in a legal sense¼.
You just opened a can of worms in my brain! And I thought I was suppose to be the ViLLain.....