That's just about as accurate of an answer as you will get... Well done Oreaopla... You just saved me a lot of typing.The short and sweet of it... Back when the semi shelf equipped hk factory guns were still importable and new machine guns could me made for transfer, there wasn't as readiy accessible a supply of conversion parts or skilled enough builders to do the factory correct paddle release and push pin conversion. It was cheaper and easier to take the trigger group and alter it to accept the sear but many of these conversions were done with the receiver being registered and not the sear. This means you must always keep the sear with this particular firearm as the sear is an unregistered conversion device. To separate the two would mean "creatin a new machine gun" after the 1986 cutoff. Many folks did this just before the cutoff in the hopes of doing a factory correct conversion eventually but the ATF declared that the receiver can no longer be altered with an unregistered sear present.
No problem. I figure I've read the whole explanation here enough times that I could save a little reading time for someone just venturing into the realm of hk roller locks. I'm still learning stuff and I enjoy reading about the way these things work.That's just about as accurate of an answer as you will get... Well done Oreaopla... You just saved me a lot of typing.