If a MP-5SD and an AR15 Pistol had a baby???

**1096369fred** · April 22nd, 2017, 06:48 AM

Hey Guys,

I just went through Phil Singltons Patrol Rifle Instructor class with full auto M-4's and MP-5's.... I fell In love with the MP-5SD... (I had a Standard POF MP-5 SBR) but the SD is an amazing weapon!
for those that dont know... the SD's suppressor overlaps the barrel, which is ported just forward of the chamber. The "bleeding" of gasses in this manner
causes all bullet weights to remain subsonic.... hence very quiet! Has anyone made an AR barrel that uses this system? it is the cats ass.... I wouldnt mind
paying the extra money for an MP-5 suppressor.... but can't reaLLY JUSTIFY the cost of a semi MP-5 SD at $2500+

Thanks!
Fred

**Nate7667** · April 22nd, 2017, 08:41 AM

First thing is the main difference is the HK delayed roller blow-back over standard blow-back of the AR.
This is the first thing that will create a smoother shooting gun. Now if you swap to a normal gas system of an AR, you will get less port noise and much less felt recoil. A buddy of mine is building one right now.
Also the Sig MPX is a piston system. I haven't spent enough time behind yet to comment. From what guys are saying it is pretty quit as well.

Having spent a good bit of time behind both AR9 and an SD, the SD is more quiet, no doubt.
I love my AR9 and im reassembling an SD very soon. But the port noise, or lack or, with the DI set up my buddy is making. Amazing. Along with felt recoil, probably close to half. Starting over, that's the route I would take.

None of that answered your question lol
Just stating the options.

I'm pretty Spikes Tactical made/makes one.
A company in Ohio that I'm drawing a blank on did for a bit as well.

You would need have the barrel ported, preferably via EDM.
Some math would be needed, or copy the amount and location of the SD barrel for the ports.
The barrel extension would need threaded to except the can. You could easily thread it to 18x1 and use a current SD can offered on the market, like TPM Outfitters.
It definitely can be done.
One issue would be having enough area to thread the extension for the can and have the hand guard also mount to the extension.

Let me rephrase that. The barrel nut would be in the way of threading the extension. You would have to make a collar or a very large barrel extension to allow the barrel nut of what ever hand guard you choose to have enough room to install and to allow the can to mount to, and be kept concentric to the bore as well. The SD cans also have an area at the the muzzle end of the barrel to align the barrel and can closer to the muzzle as well, about 4.5" out from the barrel nut/front trunnion location of either weapon.

**1096369fred** · April 22nd, 2017, 06:57 PM

Hey Nate,

Yeah maybe it is just me.... but for a 9mm AR it would be one bad ass set up! Particularly if the Hearing protection Act, by some miracle passes! I really would like to build up one of those Omega SD uppers that
Atlantic is selling but for $1750 plus lower, stocks, etc..... and the inevitable $200 to Uncle Sam......likely not gonna happen on my paycheck....

That said, if I could put together a AR-15 SD upper in 9mm and pick up a no Tax TPM can..... oh, yeah..... TAKE MY MONEY!!!

**Nate7667** · April 22nd, 2017, 08:03 PM

Anything is possible, just got to want it bad enough.
But I would guess machine time would cost as much as buying the Atlantic SD kit.

**1096369fred** · April 23rd, 2017, 06:37 AM

Interesting thought..... take an actual MP-5SD barrel and mill the breech end for a standard AR-15 9mm barrel extension..... I haven't taken measurements yet.... but it looks like it might be doable....

HK Parts as lots of the goodies to make it possible:

https://www.hkparts.net/shop/pc/view...5&idcategory=0

https://www.hkparts.net/shop/pc/view...1&idcategory=0

https://www.hkparts.net/shop/pc/view...dproduct=17400

**Nate7667** · April 23rd, 2017, 06:47 PM

Not a bad idea to start, just make sure have enough room when threading for the extension that you have enough clearance for a barrel nut for the hand guard and still can mount the SD can on the factory 18x1 threads.

I personally don't care for the SD hand guards on an AR. Other guys have done it, not my thing.

But if you're going to build it, start with QC10's MP5/AR9 lower that uses HK mags, even if they are 3x the price lol

**1096369fred** · April 24th, 2017, 08:22 AM

Hey Nate,

I had not seen that lower..... Pretty cool..... Particularly if it runs with POF MP-5 mags! I curently have a 9mm AR, that I run with a Seekins hand guard (one of the larger internal diameters!) I love it and if it will fit a SD can.... I am in business..... The only issue i have found is that most 9mm barrels do not use a barrel extention..... I will have to look at mine later and see if it could work.....
thanks!
F

Here is my 9mm ar-15:

o

**HRoark** · May 12th, 2017, 05:33 AM

Fred, check out SRT Arms. They can integrate a can into a 9mm upper.

They can build 13 and 16 inch overall lengths, and they don't normally, but I'm pretty sure they can port the barrel to keep everything subsonic if that's what you want.

**1096369fred** · May 12th, 2017, 08:49 AM

Thanks buddy..... I'll check them out.... If the HPA passes..... I am so doing this!!!
A 9mm AR that will keep all rounds subsonic, with out having to use .147's is just to cool to ignore! I'd pick up a clone SD,
But for $2500+ I'd be just as happy with an AR!