Looking for opinions on the GHM9 Gen2 SD kit.  How does the GHM9 SD kit sound relative to a suppressed MP5 (non SD version) shooting subs?  My understanding is that the gasses are vented to make even supersonic rounds subsonic - which really has my interest.....

You’re about to get a bunch of people who spent too much on blowback guns tell you it’s great, what a bunch of people who paid too much for a roller locked tell you that it’s the only way.

GO TRY IT OUT FIRST.

If you know the difference, imo you won’t be happy. But for some reason this forum has turned into “if you think blowback has too much pop or gas or recoil, ur jest a pussy”. Instead of any objective discussion as to what and how good systems work. Let alone never any evidence in the way of split times or repeatable drill performance.

So go get hands on, because you won’t get a good answer here. Either you know the difference and won’t be happy, or won’t care, or don’t know and in that case yea man do whatever.

I tried almost every PCC out there and for suppressed and competition landed on CMMG. But there is a long term reliability issue, you have to switch the injector springs out fairly frequently. I haven’t tried a GHM9, but the APC9 was a huge let-down, and the GHM is pretty damn similar. Someone here tried to say the GHM was better than the APC9 because of the long travel bolt, but if you look at the charging handle, it’s not long travel (like a sten or etc) at all.

IDK, good luck if your going to use the data you collect here. Just buy it and sell if you don’t like.

Really interested in the SD kit more than anything.... That's why Im asking.... SD is supposed to vent off excess gas so that port pop is less.  The MP5 may be king, but Im really curious if it really does make supersonic rounds stay subsonic.  I think that has alot of utility.

Its the same setup as the SD. Ports in the barrel and a reflex can.

Yes your common 115 and 124 gr ammo will become subsonic.

As far as it being more quiet than the MP5SD; well I doubt that.

Regardless it should be quiet

Theres not a huge difference between my MP5s suppressed with subs and my SD with 124 gr ammo. Its a little quieter but still in the same neighborhood.

I don’t fully understand the draw of ported systems. In normal times, 147gr or heavier ammo isn’t that hard to find or that expensive for when you wanna be as quiet as possible. Dropping 115 or 124 down to subsonic just seems like it would make hollowpoints fail to expand properly. There is no “off” switch that I’m aware of, so wouldn’t it slow down 147gr too?

Yes it will slow down anything you fire out of it, including 147gr.

The prototype HK SMG that was the predecessor to the UMP was the only gun I know of that had a selector to allow you to open or close the ports. I wish someone would make a modern design with that feature, it's really cool.

B&T cost cut that out of the APC9

An interesting part of HK's JSSAP effort was the design change from delayed-blowback to simple blowback.  The initial HK54A1 still used the delayed-blowback roller-locked bolt but that was changed to a closed-bolt unlocked breach in the subsequent SMG & SMG II development.  As noted by Jim Schatz (2014) in the Small Arms Review on the subject, "The fact is when timed and firing short bursts, the results on the target - round placement and group size - between the roller-locked MP5 and the simple blowback operated weapons like the SMG are generally indistinguishable."  It was after these prototypes, that H&K developed the Navy/N models of their MP5 series.  The MP5SD-N did not include the prototype gas relief valve.

Correct

The draw in my opinion is you can use whatever ammos you have to be quiet. It also is a tiny bit more quiet than a conventionally suppressed gun with subs(generally speaking)

In the case of my MP5SD it also get much more filthy. I would have to assume all ported designs like it will also.

I wont sit here and say its for everyone. Its not. But boy oh boy I take my SD out more than any other gun. It shoots super smooth and its incredibly quiet.

Cost of entry to an MP5SD just seems too high to me though, which is why I inquired about the GHM9SD kits.  APC9SD is another option but a tad bit more expensive than picking up a ghm9 and SD kit up separately.

I have an MP5SD and an APC9SD, I have swapped the cans between them and the APC is noticebly louder than the MP5. I am not saying it hurts or anything like that, but my APC9SD (its running the compact can keep in mind) is around the same loudness as my full size MP5 with an octane 9 on it. However I think the SD idea is super cool so I dont regret my APC9SD purchase at all. Its also a lot easier to clean than my MP5SD

I think the selling point of the SD systems is obviously turning supers into subs.  The B&T SDs (GHM9SD and APC9SD) are much less expensive to get into than the MP5SD to accomplish that selling point.

For me, it’s justified to look into some more if supers shot from a B&T SD (whether from the APC9SD or the GHM9SD) are quieter than supers shot from lets say an MP5 (the king of suppressor hosts).  Then in that case I think its worth throwing some $ at.  Solely from the perspective of not having to hunt for subs, which were rarely on the shelves of the big box retailers pre-covid - much less so these days.  If only B&T would pick up the production on these so we could have more consensus on what they offer over the standard MP5 platform.

It is regrettable that the suppressor in the GHM9SD kit is not interchangeable with that from the APC9SD.   I wonder what was the main reason B&T decided the GHM9SD must have a different suppressor from the APC9SD.

Total speculation, but I wonder if the reason we haven’t seen any GHM9SD kits is that B&T went back to the drawing board on that and is maybe redesigning the GHM9SD kit to accommodate the same suppressor as the APC9SD - get some economies of scale going.  I would think B&T would be able to do this pretty easily since the GHM9 does offer that modularity with the front end changes (barrel, handguard, etc.) unlike the APC series.  Seems like it would draw more US sales to both the B&T SD offerings - essentially only needing 1 suppressor (1 tax stamp too) for both the GHM9SD and the APC9SD.  Would be nice....

MP5SD clone, 124 HSTs @ around 15yards IIRC. I know it's clear gel, and I shot it bare, but it's what I have available.

Are you talking suppressed supers or subs out of the full size MP5 when comparing to the APC9SD?  If the APC9SD still sounds like supers out of a suppressed full size MP5, I may scrap the whole idea.

I have both the compact and full-size SD cans.  The compact can is definitely a few decibels louder than the full-size.  The full-size suppressor is quieter due to the additional baffles and volume.  I agree that the SD with the compact can sounds equivalent to a PCC with a traditional threaded or 3-lug suppressor with subsonic ammo.  My MP5 is a little quieter at the ear due to the delayed blowback.

With supersonic ammo, the SD eliminates the supersonic crack of the bullet and hence is much better for suppressing supersonic rounds when compared to a non-ported barrel.

Thanks for posting that. That makes things more intriguing to me. Otherwise it seems like an expensive way to make a .380 out of 9mm, but if it still behaves like a 9mm on target, that’s the only place it would matter in my mind.

So, with the SD (full size can) running supers, it would likely be quieter than a suppressed MP5 running supers?

Also, how long is the compact can?  I think the full size is huge at 11.5ish”

I used to have chrono data that went with this. I need to revisit it in the future, following the testing procedure closer. I now have another block of gel, it should catch the ones that might escape the first block. Maybe if ammo becomes more available.

Yes, quieter with supers.

8"



and full size:

Beautiful!  Thanks for the feedback. Im really wanting to set up a GHM9SD.  Id imagine the GHM9SD would probably fall somewhere between the compact and the full size can on the APC9SD.  I want to say the suppressor on the GHM9SD kit is 9.8” or so.

What's the approx "all in" price for a GHM9 with the short suppressor SD kit?

I paid:

GHM9 w/Telescoping Brace = $2,100
SD Kit + Tax Stamp = $1,400
Selling Stock Barrel Kit = -$300

Total: $3,200

In the long run an APC9SD is going to cost about the same. I already had a standard APC9 Pro, which you can't add an SD kit to after the fact, so I went the SD route on my GHM9. I don't regret it one bit.

Can you speak to the sound performance of the GHM9SD with supers relative to subs with other hosts?

It's about the same honestly. I've fired my APC9 Pro with a Rugged Obsidian and 150 gr. subs back to back with the GHM9SD with 124 gr. supers and I really can't tell a difference. If there is, it's only a few dB's.