[Lohe]

First off, you can't just buy an MP5 receiver. It is considered a machine gun. You can buy an older HK94 but it'll cost you!
Several companies make pre made receivers and several members here make either receivers or full firearms.
Chopstix Kid and Ghilliebear are probaby the 2 most talked about people on the board who do either receivers,
partial builds or full builds. They both make GREAT stuff.
Other than that, you can buy a "flat" and roll it and weld it and finish it yourself.
You have a LOT of reading to do.. I suggest reading a lot in the reference section.

The UMP is less expensive to manufacture than the roller lock rifles. They are probably also
less durable. Parts for them are going to get hard to find unless they get more popular and
someone starts making more replacement parts for them, unlike the roller lock rifles.
You're also looking at $1,200 and up to buy an HK USC and another grand or so (or more)
to convert it to a UMP (semi of course). Then you're going to have problems getting mags
for it until someone steps up and makes U.S. mags for it. But the UMP is really cool!

 

[Chopstix Kid]

Lohe pretty much summed it up. The LSC flat is currently the most accurate to genuine HK specification that is readily available. That being said, you also need the right builder to roll it into a receiver. No matter how good the flat is, a bad roll job can ruin all that. If you can find an MKE flat, that is a Turkish flat stamped with licensed HK tooling. There aren't many left and when they come avaiable, the are quite spendy as they are the closest thing you will find to a genuine HK flat. Do note however, that the MKE flats were imported prior to them making it to final stamping. As such, a lot of work is involved in turing those into a firearm.

If you shoot both the UMP and MP5 (even both in 9mm) they are two completely different experiences. Take your BMW for a nice stroll on the Autobahn; that's an MP5. Now take your BMW for a European off-road excursion; that's a UMP. The bolt ina UMP is nearly the same weight as the rest of the firearm. As such, it creates a great deal of rocking motion, or as I like to call impulse, while shooting.

 

[k9enroute]

?

Thanks guys for the heads up. Next question?
Why do non of the flats i see have the front push pin wear the trigger pack goes?
It's either non existent or a fake pin rivet?

 

[JeepGuy79]

Thanks guys for the heads up. Next question?
Why do non of the flats i see have the front push pin wear the trigger pack goes?
It's either non existent or a fake pin rivet?

you put that hole in a semi gun and u just made a machine gun.

 

[k9enroute]

Not that I am saying you are incorrect jeepguy I am just curiouse why are there clones title 1 that have the push pin holes and why do hk94s and so on have that whole? They aren't machine guns?

 

[Lumbergh]

Hmmmm. BMW. It's a good thing.

 

[Chopstix Kid]

Not that I am saying you are incorrect jeepguy I am just curiouse why are there clones title 1 that have the push pin holes and why do hk94s and so on have that whole? They aren't machine guns?

There are no clones with an open push-pin hole unless it was made by a C2 SOT as a post-sample. Will will from time to time see pre-86 transferrable push-pin conversion guns. Per the ATF, a functioning front push-pin hole is what consitutes the receiver as being a machine gun. The MKE firearms do have the hole which has been plugged... which is an entire topic all in itself.

 

[Lohe]

Not that I am saying you are incorrect jeepguy I am just curiouse why are there clones title 1 that have the push pin holes and why do hk94s and so on have that whole? They aren't machine guns?

H&K 94 9mm Heckler & Koch HK94 : Semi Auto Rifles at GunBroker.com
Look at the 3rd picture down. Under the mag release is a chunk of metal that
the forward part of the lower rests on.
That is the difference between a machine gun upper/lower and a legal one.
You'll see the parts listed as "weldments", more specifically a "shelf".
If you see a push pin in that location on a lower it's okay because the
lower is not considered the firearm, by law, unlike an AR.
If you see a push pin in that location on the upper receiver that is
NOT OKAY as that means it is legally (or illegally) a machine gun.
What a lot of companies like Hkparts does is clip and pin the lower,
which makes it look like it has a pin there but it really does not.
So what you might be seeing is a clipped and pinned lower and thinking
it's really a pin, which is the whole point!