I've played with a couple different bullet and powder combinations for my Walther PPQ 4.6" threaded barrel.

115 gr Barnes TAC-XP:

N320 3.5 gr = 1047 fps (1.14" c.o.a.l.). Single digit SD's. Super accurate, quiet and clean but didn't run 100%. Seemed slightly underpowered, although Vihtavuori says this is a max. load.

N320 3.7 gr = 1068 fps (1.15" c.o.a.l.). Again, single digit SD's. Didn't care for the recoil impulse, but still very quiet and clean. Ran 100%. Very accurate.

BE-86 4.3 gr = 1061 fps (1.14" c.o.a.l.). Single digit SD's. Not as quiet as N320, but still quiet/accurate/clean, ran 100% and felt like it should have been going faster. Nice recoil impulse.

BE-86 4.5 gr = 1083 fps (1.15" c.o.a.l.). SD @ 16, but this charge or 4.6 gr would be an ideal load for upper limits subsonic with this long bullet.

124 gr X-Treme RN-HPCB:

N320 4.1 gr = 1055 fps (1.14" c.o.a.l.). Single digit SD's, accurate/quiet/clean/ran 100%. Didn't feel underpowered but it's also close to max. per Vihtavuori.

BE-86 4.9 gr = 1122 fps (1.14" c.o.a.l.). Accurate and clean with nice recoil impulse. Right on the upper edge of subsonic. Downloading to 4.7 gr or 4.8 gr will be ideal with this bullet.

All in all, N320 is an outstanding powder for target shooting, but I'll take BE-86 over it all day long, both for suppressed and for +P.

I'm not sure where you live with what temps elevation etc. but all those seem to be dancing on the edge of subsonic.

Southern Nevada. We don't see too many cold spells here.

quote:

Reading around, I'm also seeing that the colder it gets, the more likely it is to go supersonic, if the posts I'm reading are true. Given that I've been shooting it in 100+ degree weather and it's finally starting to cool off, I guess I'm going to find out soon. Kind of a disappointment.

I took a bunch of the American Eagle AE9FP out a few nights ago. Where we were shooting, it started in the low 50’s and it got down around freezing before we were done, and every round of it that I fired was super sonic. So disappointing.

I also use the Speer Lawman 147 gr. 9mm ammo.

quote:

Originally posted by 10X-Shooter:
I also use the Speer Lawman 147 gr. 9mm ammo.

This was surprisingly quiet in my 9mm AR too. I expected it to be right on the ragged edge given my 8" barrel and relatively cool temps, but the 115gr cheapo white box was much louder.

I was under the impression that the Lawman is supposed to be full-power practice ammo that replicates duty loads of the same weight.

Anyway it sure looks like velocity matters a whole LOT with suppressors.

Lawman is just a bit slower than AE9FP in spec terms. BUT I have not had AE9FP go supersonic here in Maine in below freezing temps but not silly low temps. (I'm not going shooting in below zero temps). So it seems odd it would go supersonic around freezing? But what barrel length are we talking?

quote:

Originally posted by hrcjon:
Lawman is just a bit slower than AE9FP in spec terms. BUT I have not had AE9FP go supersonic here in Maine in below freezing temps but not silly low temps. (I'm not going shooting in below zero temps). So it seems odd it would go supersonic around freezing?

I don't know if the case I got was loaded a little hotter or what. I found a YouTube video with a guy testing out various subsonic 9mm loads, including AE9FP. I commented my experience, and he replied saying that further testing he did with some friends concluded that it was the quietest of what they had been testing, and was surprised I had such a bad run with it. It may be that it's generally just fine, and I got a case of it that was loaded a bit on the hotter end. All I know is I'm not going to bother buying more of it. Between it going supersonic, it being louder then similar 147gr loads even when it didn't, and finally that it likes to choke up both my Stribog and my Scorpion, I think I've bought all of it that I'm gonna buy.

quote:

Originally posted by hrcjon:
But what barrel length are we talking?

Scorpion - 7.7"
Stribog - 8"

I know a lot of guys will go for 4-5" barrels in platforms like these to ensure rounds don't go supersonic. I chose not to based on some commentary you provided about a year ago to the effect that shorter barrels, while helping keep velocity down, also mean more unburnt powder burning up in the can and the same suppressor not being as quiet on K guns as on, I guess what we'd call a "full size" gun where it doesn't have to work as hard. IT makes sense to me, but if I misunderstood you, please correct me. Based on the fact that the AE9FP was noticeably louder suppressed than all the other 147gr ammo I've tried, I don't think a K length barrel would've made the difference.

Just my musings on the experience.

So far in my more recent testing, I'm really liking PMC Bronze 147gr round nose. It's fairly cheap, has fed reliably in everything so far, and has been consistently quiet.

It may amuse you to hear that my friends are all buying MP5 clones and have managed to convince me of the "need" for one. I'm gonna get to shoot a Hi Tec built MP5SD clone in a few weeks. My friend who owns it says it's the quietest, silliest, most fun gun in his collection, and his tastes and collection are similar to yours, based on things you've posted over the years. It remains my opinion, having grown up on an HK91, that the HK designs of that era have an awful manual of arms, clunky ergonomics, and dogshit triggers as a feature and not a bug... but it remains the case that the MP5 is iconic and cool as shit. If you want to shoot quiet 9mm in style, you can't really go wrong with one.

This is a bit odd to me. I shot a couple of hundred rounds through my APC9 (6.8" so not really shorter) testing gas on a couple of new cans at 38-40d F and not one of them went supersonic. Maybe I'm the lucky one as these are all from the same lot.
An MP5 is a giggle machine, there is no downside despite all the silly ergo, operational, reload trigger etc. issues. Slap and shoot and enjoy... An SP5SD would seem to me to be a way better giggle machine (I don't own one though). My latest try in this area is that my drug dealer (oops class 3 dealer) has one of the new B&T printed SD cans coming and I'm going to give a go at building one off an APC9 or an MPX with the ILWT barrel.
I don't often say this but there are some guns you should just own and an MP5 style is just one of them. go for it if possible.