I am looking to build a MP5 clone, but I am not sure if I should go Regular MP5 or K. What are the pros and cons of each?

Is the polymer lower for the MP5 similar in feel to the G3? I really didn't like the feel of the G3 polymer lower and put the metal lower back on as the grip felt better in my hand. I also feel the SEF safety switch is difficult to for me to manipulate on the G3 lowers. I assume the MP5 lower would be similar and I should look at possibly look at getting getting a Navy or FBI lower? Are the trigger packs swappable between the the SEF and Navy/FBI lowers or do they take different trigger housing?

Trigger boxes are interchangeable between all, 91/93/94/MP5/MP5K. Only difference being the ejector and hammer spring. The box itself is either what most refer to as SEF box or there is the Navy/Ambi. The ambi has different internals due to ambi selector. Both need their own poly housing due to the different safety/selector as well. The K housing is one in itself due to mounting. MP5 uses a single pin stock mount while K uses 2. MP5 has 8.86"ish barrel, MP5K is 4.5"ish. What runs subsonic in the K with a can may run super in the MP5 due to extra barrel length. That brings me to my next point, the K requires a certain locking piece to run a can where the MP5 uses the same with or without a can. The K is more concealable if thats your desire. I guess its all depends on what you want to do with it? If it were me and you are hell bent on building one, I would personally do a full size MP5 first. Then if you desire, the K.

Are you building this yourself or having it done by a reputable builder? Do your homework if yourself, its not for the faint of heart and best done with genuine HK parts. And if something goes south, it's tough to get a builder to touch it. If they do, you should have just went with them to begin with due to added cost. Not dissing ARFCOM but there is another site that is dedicated to roller lockers that you can get a butt load of info and builder recommendations if going that route.      

 

To be clear, the trigger box (the metal frame that holds the internals) is different between the SEF and the Ambi lowers because of differences in the safety levers.  You can’t put a Ambi trigger pack in a SEF lower, or the other way around.  The term “Navy” has been used by some to refer to the polymer SEF housing, which still has SEF internals.  Others consider the ambi pictogram housings, which are all polymer, to be the “Navy” housing.

The plastic grip on a steel G3 trigger housing is very similar in feel to a polymer MP5 “Contoured” trigger housing (which is named for its subtle finger swells, arched palm swell, and thumb rests indentations). This hand-filling grip can be too large for individuals with small hands and/or short fingers, making it difficult for them to reach the safety selector.

This is why the “Navy/Ambi” style “straight grip” trigger housings are also popular. The Navy/Ambi grip is more narrow than the Contoured grip, which allows for a shorter reach to the safety selector.

Some folks also prefer the “bullet pictograms” which are stenciled onto the sides of most Ambi trigger housings, rather than the simpler “SEF”, “URJ”, “0 1 30”, etc. markings typically present on Contoured trigger housings, even when used on semi-auto only firearms.

To add one more variant to the mix, there is a Navy trigger housing which is marked SEF, just as is the Contoured trigger housing. Both of those use the same SEF trigger pack and (polymer style) safety selector. Some MP5 Navy SEF trigger housings have been made by modifying former German Bundeswehr G3 SEF polymer trigger housings. It’s a very easy modification, and those trigger housings are relatively cheap, making this a popular choice.

I have been looking at the build kits from robertrtg and hkparts. Any other reputable places for kits? I think I would just go with a FBI or Navy lower, but of course they cost more then the SEF ones. The K kits from both are 5.5 barrels as they have the 3 lug mount on them, so a little longer than the standard K barrels.

I went to get a k parts kit and had it in my cart. I was looking at folding braces and some other parts, then went to checkout and the the parts kit went out of stock.

Don’t build a K unless you are going to SBR it.

I had a reverse stretch for a short time.
Without the vertical grip, the tiny handguard will get too hot to hold after a few mags in semiautomatic.
With a binary trigger it would be worse.

After getting the RS I realized that what I really wanted was a full size MP5, so that’s what I’ve got now and I love it.

Since most of Arfcom has multiple houses on different continents, the correct answer is GET BOTH!

You should definitely at least get a fullsize and a K.

I only have one house, and I shot my select-fire MP5-N in the yard there this afternoon.

Get the lower you want. Yeah the Navy lowers cost more, but nothing else looks like them.
I'd go with the longer MP5K-PDW barrel. It keeps your options open for a 3-lug suppressor (or just a flash suppressor if you want that).

I think you'd be better off buying a complete clone instead of building one from a kit, but it just depends on what price you can find a kit for, and what your skill level and tool inventory are.

This is solid advice if you want a smaller gun.

I have either owned or been issued:  MP5N, MP5SD, MP5K-PDW, MP5K and think that the full-size MP5 is the best version, but if you want a smaller gun, get the PDW barrel for the K.

I have the MP5 and the k version. Both are a lot of fun. Braces on each and I may SBR the K for the vert foregrip.

I'm in a no NFA state ( apart from some SBRs) so suppressor fun is out but maybe not for you.

That being said, the K is very fun to shoot!

What ever you do, avoid the flats and kits at HKParts. Mine was out of spec and a real mess to build on. Their trunnions suck too. I built it anyway, but it added HOURS to the project.
Your MMV, but that was my experience. The 5 kit I got from robertrtg.com was a breeze to build and the flat folded and built sweetly.

I have the MP5-A3 and MP5K-PDW versions.

Get the Navy/Pictogram/Ambi version. It is MUCH easier to reach the selector than an SEF/Contoured lower.

The MP5 fullsize is SO SMOOTH to shoot and manipulate the cocking lever. This is not true of the K gun. However, the K gun setup as an SBR is the coolest gun ever. I just feel the cool ooze out of it. The shorter cocking lever is harder to manipulate as easily or fast, especially if you want to run optics (the mount is SO close to the cocking lever it chews up your hand when running it hard).

Zenith told me to keep the standard locking piece in my Z5P when running suppressed, so there's that. I run mine almost always suppressed with either an Octane 45 or Omega 9K on a tri-lug mount.

I really wanted the mp5k because it was more compact. I would have done it with the 5.5 inch pdw barrel, but I don't see any parts kits for these around. HKparts has various full size mp5 parts kits, but I was trying to stay away from them, who else has parts kits in stock and is reputable? I see botach.com has some, but I heard some not so good things about them as well.

Is the benefit here “building” for the fun of it?

If not, why not just get an SP5?

Build for the fun. I also thought the parts kits seemed a little cheaper through robertrtg then an SP5.