View Full Version : Making an HK 51

September 12, 2002, 07:47 AM
I have a family friend out of state who has a registered MP5 auto sear. I also have another connection which I think will get me an HK91 (the real deal preban, HK marked). The question is, will the "MP5" auto sear work in the HK91, and how much should I be willing to spend to obtain the HK91 if it's in like new condition? I think the guy might part with it for about 1500, but being in California, I have no idea what these things go for these days. My plan is to have it constructed out of state, and sometime later in life I'll pick it up when I get out of here (Kali, that it). Thanks for any help.

P.S. once a gun is a legally registered machine gun under the NFA, do I have to ask anyone or get permission if I want to suppress the same gun? NFA is NFA right? Along the same lines, shortening the barrel to less than 16" should also be OK, right?

September 12, 2002, 08:42 PM
Don't know about the HK in particular, but as far as suppressors go you can put a suppressor on any gun you want, as long as it's not a post-ban semi-auto rifle with more than one evil feature (a sound suppressor also counts as a evil flash suppressor.) Machine guns aren't limited in barrel length or overall length like a rifle either.

4V50 Gary
September 14, 2002, 12:12 PM
The trigger groups between the three (7.62mm, 9mm and .223) are very similar and to some extent, are interchangeable. However, I have no expertise on "home brew" conversions like "drop-in" auto units. Each much be examined individually for viability.

BTW, it's more than a sear and you must have a "trip" unit that is actuated by the bolt carrier for proper timing. A regular bolt carrier may be modified, but it's probably better to buy a used full auto one. Those things don't wear out. Shake one if you get a chance. Sounds like a salt-shaker. It's wolfram granules inside.

September 14, 2002, 04:23 PM
:) That's the first time I've ever heard anyone refer to Tunsten as Wolfram.

Also, my assumption here is that the semi-auto receivers are the same as the full auto receivers, with only internal differences and the lack of the selectable trigger group, I'm thinking that the 3 or 4 position trigger group will work with the semi auto receiver. Thanks for you help so far, I appreciate it.

Johnny Guest
September 15, 2002, 12:16 AM
Regarding the suppressor - - --
Doesn't matter if you have a legal auto sear, the SEPARATE suppressor must be another reistration. Think, if you will, about the MAC 10 and 11 series. Register the gun, fine, but any suppressor you add to it must be on a completely different form 4. ie: TWO $200 tax stamps, not one.

Only exceptions I can think of are the guns which have the built-in features. MP5SD is a machine gun, but has an integral suppressor. A DeLisle carbine is BOTH a short-barrelled rifle AND a suppressor, but they can't be separated. (Normally, that is.) One registration for the gun with non-detachable suppressor.

If you wanted to put the auto sear into the HK91 now, and maintain the option to stick it into an HK94 later, fine---But to make the HK94 carbine LOOK like an MP5, you'd probably want to have it converted to proper length barrel, which would be another registration.

As always, you should carefully check the applicable laws and regulations YOURSELF. You really wouldn't want to risk a misstep that could cost you a LOT of money, and possibly even some time in jail, relying solely on advice from somebody you'll probably never meet. This sort of exchange on TFL is just us guys trying to help other members be aware of stuff that could cause problems.;)


September 15, 2002, 03:01 AM
I know another guy who might be willing to part with his SP89, which looks to me to be nothing more than a semi MP5. Am I correct in this thought? Could I convert the SP89 into an MP5 with the auto sear? From what you are saying, though, I could not add the collapsible stock even if I had the auto sear installed because that would require another $200 tax. Just wondering, and thanks for the help. Living in California leaves one a little in the dark regarding the laws on class 3 stuff.