The 9mm ones do not have a bolt hold open feature. A "real" MP5 9mm bolt does not hold open on an empty mag.

40 cal models do, I think 10mm does also?

 

40 cal and 10mm essentially the same gun. Different barrel, different locking piece (sometimes), but the same gun (even the same mags).

 

Doesn't exist in 9mm... Not even sure about getting one in the realm of the custom builders... I know Joe (Dakota Tactical) took a shot at building/designing on once. Not sure if he got it to work right or not. He said it was a massive PITA and would never do one again... EVER!
So, Can it be done... I guess.
Rainbow unicorn season isn't open yet though.

 

I got as far as getting the device on the receiver but then ran into issues with the mags... the modifications to the body and follower were a bit more than I wanted to chew.

 

Ha!! Thanks guys. My apologies. I "thought" the MP5 that I shot back in the late 90's had the bolt open after the mag emptied. I don't have an "actual" MP5 now...only civ style.

So with the information presently at hand....what is different between 40 cal set up and 9mm that would prohibit a 9mm from having that feature? I don't have a 40...so I really can't compare. Thanks for any information in advance.

 

40/10 has a catch welded on the left side. They're pretty finicky.

BHO's aren't that valuable in my opinion...

 

Generally, guns that have bolt hold open have mags (especially followers) designed for that function. Then there's welding the mechanism on the side of the receiver. Probably cocking tube support, and other stuff I have forgotten and don't feel like thinking about.

 

Got it.....thanks guys.

 

I wonder if you could build a follower for the mag like the followers in Yugo AK mags that catch the bolt carrier from moving forward after the last round

 

What would happen after you removed the spent mag?

 

The 9mm receiver and .40 caliber receiver are different. The .40 caliber has an indentation for the bolt hold open mechanism. So I'd think the 9mm receiver would to be modified for that or change the magwell of a .40 caliber receiver for 9mm magwell. Also either the gun would need to be adapted to Colt 9mm mags (because that 9mm mag has a bolt hold open activation device), or each HK style 9mm mag would need to be modified to add a bolt hold open activation device. Could it be done? Of course it could. But finding a smith capable of doing it with the time to devote to the development and finding enough funding to do it? If you remember the gun having a bolt hold open feature, then I'd think you shot a MP5-40. Or you don't remember the experience exactly and the 9mm gun didn't hold the bolt open after the last round fired. Either way, could that feature be added to or built into a 9mm MP5 clone? Absolutely, but unless a competent builder that wanted to do it and enough money to pay for the development, I doubt if it would ever be done.

Scott

 

I understand it was a pain to develop it for the 10mm series. We'd have to get a new magazine design, and they're finicky enough as it is.

 

Seems to me that if you started with the 40/10 and changed the barrel and bolt face to accommodate 9mm, you'd just be left with redesign of the magazine which I agree is no small feat - if you look at the HK 10/40/357 magazine, you'll notice that they don't age well while being used so you have to wonder why HK didn't make these from metal

 

... - if you look at the HK 10/40/357 magazine, you'll notice that they don't age well while being used so you have to wonder why HK didn't make these from metal

Weight and cost.