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Posted: 5/9/2026 4:21:58 PM EDT
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Figured this would be the best sub forum for this. So 147gr 9mm ammo is considered to be subsonic. However, (as I understand it and feel free to correct me) at altitude and lower temperatures, speed of sound decreases, thus, making a PCC shooting 147gr with a can on much louder due to supersonic crack. Think around 10k feet and a chilly day. What is the slowest ammo you guys have found to fix this issue? And hopefully not $1 a round lol Also, was thinking that the bullet may travel faster due to reduced air density further compounding the issue? |
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OK, there's a lot going on here It sounds like your PCC shooting 147gr bullets is supersonic. If this is the case and I think it is, your PCC is going to be supersonic at elevation I said "I would have to chronograph your ammo out of your gun with the suppressor attached to make a guess what it'll do at altitude". I really need to know what your PCC chronos at with 147gr bullets to get some kind of a baseline. There is Seismic's QuakerMaker 185gr rounds that sell 21 cartridges for $29.99 not including tax and shipping. This is well over you $1.00/round budget. |
| The Federal Syntech 150gr sounds like a winner and the price is right but I have doubts if an extra 3grs will make any difference in a 8.3" barrel PCC. It would be worth a try and really interesting to chrono the 147gr and the 150gr to see the difference in fps |
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Originally Posted By EliCustom: The Federal Syntech 150gr sounds like a winner and the price is right but I have doubts if an extra 3grs will make any difference in a 8.3" barrel PCC. It would be worth a try and really interesting to chrono the 147gr and the 150gr to see the difference in fps |
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Originally Posted By CJofFL: It’s not the weight of the bullet, it’s the charge in the case. I understand this but the round needs to be able to cycle the action. You can't increase the weight by a slight amount and decrease the charge by a lot and have it cycle the action The PCC having an 8.3" barrel is what makes it difficult to keep rounds subsonic even with heavier bullets. |
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Originally Posted By EliCustom:I understand this but the round needs to be able to cycle the action. You can't increase the weight by a slight amount and decrease the charge by a lot and have it cycle the action. The PCC having an 8.3" barrel is what makes it difficult to keep rounds subsonic even with heavier bullets. |
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If you want true subsonic, that barrel is a bit long to be optimal. You really need a barrel similar to the HK MP5SD if you want true subsonic. A good can will deal with the gas well, but the supersonic crack will be the same. For subsonic, my MP5SD will work with 115gr NATO-spec and everything else, all while staying subsonic. My MP5 will be subsonic in East Texas with heavy 9mm. |
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| I agree that in general as you go up in bullet weight you go down in velocity as in 'general', you are approaching +P pressures. But that is in general and as mentioned you can find 147grn 9mm listed at anywhere from 900fps to over 1100fps +P ammo. Most Federal 147grn 9mm is listed at 1000fps from a 4" barrel, CCI has two Blazer loads listed, one at 950fps (no barrel length noted), and a Suppressor load at 900fps. I'd imagine they give the suppressor load a few less grains of powder to assure subsonic velocity out of a longer (SMG) barrel. Most 9mm pistols will be in the 4"~4.5" barrel length but most SMG's will be anywhere from 5" on up, MP5 8.8", Uzi 10.2, CZ Scorpion 7.8". All will get more velocity out of the ammuntion up to a point, probably somewhere past 10" barrel as by then the powder expansion will be spent. |
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Originally Posted By sidpost: Curious about your can and that rifle. Thinking about getting one as well. The DD is pretty sick. Well made, AR ergos, shoots really nice, and even though the barrel is a touch longer than I wanted, I like the fore hand position. It is also blowback but recoil is nice. Couple draw backs...it has a buffer tube so take that for what it's worth. She has a touch of gas, but I added what I like to call 'mud flaps', had a couple of those old magpul 1913 rail covers behind the optic and it adds just a bit of protection from the ejection port. Trigger is meh but ar15 type The B&T SQD-M 9 is pretty nice. I have it on a trim-lug, my first tri-lug and I like it. The modular aspect is very cool. I don't have scientific readings but the short variation is louder, but not much more than the long. I use the flow through end caps as I didn't really notice a sound difference with the closed end caps and with the closed off end caps made the blowback DD PCC recoil harsher and add some gas to face Overall its a sweet setup, not the most compact but I do really like it |
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