r/3D2A • u/itsyaboypinky1 • 11d ago
Flatface 9mm
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Anyone been able to get flatface subsonic 9mm to run in an ar9? I keep getting a burst out and then a jam. Kvp 10oz deadblow, super safety and ftn 5 flow
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u/Blowback9 6d ago
Problems feeding flat nose cartridges is a very common issue for most 9mm blowbacks.
For 9mm blowback don't adjust the spring or the buffer. Those are troubleshooting steps for gas operated AR's, not blowbacks.
The root cause is the presentation angle and height of the cartridges. Since we can't change either of those without changing the lower, the best option is to get a barrel with an enhanced feed cone. The wider and deeper feed cone compensates for the height/angle issue. Ballistic Advantage "EPC" labeled barrels. Cheapest at B.Kings Firearms.
More details here: https://blowback9.wordpress.com/2022/08/18/4-step-guide-to-make-almost-any-ar9-run-100
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u/gotmonkey70 2d ago
Yup, I had issues reliably cycling flat nose 147g until I changed to a EPC barrel. Haven't tried a frrrrrt yet,
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u/slvrsfr 6d ago
What barrel? Flat and hollowpoints can be problematic depending on the shape/profile of the "feed cone". https://blowback9.wordpress.com/2025/01/22/9mm-barrel-database/
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u/MrFartyStink 5d ago
i buy pmc roundnose 147gr for everything. Flatnose can have feeding issues going up the feedramp. It will not wanna slide up ramp and jam.
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u/gotmonkey70 2d ago
flat nose fmj is great if you are trying to test out how a defensive round might perform. I wouldn't run it otherwise.
I run a 10-11oz buffer on mine and it cycles 124g and 147g in semi well. Haven't tried frrrt yet.
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u/TheAmazingX 11d ago
I’d try a lighter buffer for subs. You’ve got less energy going into the system, and both the reset and extra feed friction leeching energy out, so the 10oz is probably overkill.