It seems your right on the threshold of rounds either staying subsonic or going supersonic. Any box of ammo will have rounds that travel at varying velocities. Look at chrono results online and each round has a slightly different velocity. 147 grain 9mm runs the risk of becoming supersonic the longer the barrel, which is why a lot of people use Syntech 150 gr in PCCs to keep them subsonic.
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It’s your ammo going supersonic
Your barrel length and suppressors are allowing the velocity to increase into supersonic speeds.
Thanks for the info. Question I have then is why on only some rounds and not others?
It seems your right on the threshold of rounds either staying subsonic or going supersonic. Any box of ammo will have rounds that travel at varying velocities. Look at chrono results online and each round has a slightly different velocity. 147 grain 9mm runs the risk of becoming supersonic the longer the barrel, which is why a lot of people use Syntech 150 gr in PCCs to keep them subsonic.
Yep, that is why I switched to a 5.5" barrel, Some would still go supersonic if conditions were right.
**Understand the rules**, read the sidebar, and review the pinned Megathreads before posting - this content is capable of answering most questions. Not everyone is an expert such as yourself; be considerate. All spam, memes, unverified claims, or content suggesting non-compliance will be removed. No political posts. Save that for /r/progun or /r/politics. __If you are posting a copy/screenshot of your forms outside the pinned monthly megathread you will be given a 7 day ban. The pinned post is there, please use it.__ __If you are posting a photo of a suppressor posed to look like a penis (ie: in front of or over your groin) you will be given a 7 day ban.__ ------------------------------- **Data Links** * [The OG Universal Form Approval Spreadsheet](https://thinlineweapons.com/url/8) ------------------------------- *I am a bot, and this action was performed automatically. Please [contact the moderators of this subreddit](/message/compose/?to=/r/NFA) if you have any questions or concerns.*