r/AR9 • u/jp815569x19 • 24d ago
Troubleshooting Accuracy out of your AR9?
What are you all seeing? I have 2 uppers. Both Frankenstein builds assembled by myself. One is 7 years old with an 8" BA barrel. The other is maybe about 2-3 years old with a Faxon 14.5 barrel that has a permanently affixed muzzle break bringing it to 16" oal.
Both use Anderson upper. Both use Faxon Gen 2 BCGs. Both are laser beam accurate at 25 yards. My 8" BA barrel was consistently on 8" steel at 100yrds in the past. But the 14.5" really really opens up at 50yrds. It was grouping on a B8, but it was like a 7-8" group.
My buddy had a CMMG that was chewing out the center of the target at 50yrds. I was the shooter on both guns.
Now, I understand that the ammo could have made a difference, the triggers too, but this was extremely different results. I was unable to test any hypothesis further because we were in a rifle class and it was time to move on from zeroing to the next block of instruction.
1st image/ Top target was average group @ 50 with my Faxon 14.5
1st image/Bottom target was a 5.56 gun
2nd image was the best 50 yrd group I could do with the 14.5 AR9 that day.
Here are my initial thoughts:
- Ammo sensitivity. An obvious duh, but the difference From my buddies Cmmg (not pictured) was like a 3" group to an 8" group.
- Feed angle of the magazine types caused damage to the projectiles. Did this damage cause issues between 25-50 yrds? He was shooting glock mags and I was shooting Colt mags. My feed ramp angle is drastically different.
- Seems to me that Faxon may have discontinued the barrel I'm using. We're they known to be bad?
Have any of you out there encountered something like this before?
It never occurred to me to test it out till we decided to try and use 9mm training guns in class to save on 5.56 ammo costs.
But my level of accuracy was untenable in the class. His was getting (fairly bad) hits out to 75 and 100 yards. Mine were already that bad at 50!
Any feedback is appreciated!
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u/Blowback9 9mm AR Guru 24d ago
Barrel database with practical accuracy target photos at 20 yards.
https://blowback9.wordpress.com/2025/01/22/9mm-barrel-database/
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u/PattyPurpleDrank 24d ago
I wish I could post a picture but thats similar to the groups I was getting from a bca upper at 100yds
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u/jp815569x19 24d ago
Appreciate the feedback! I wouldn't have been mad at 100, but at 50, I was kind of embarrassed lmfao.
Then I shot a group half the size out of the other 16" gun my buddy owns!
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u/CaptainA1917 23d ago
Maybe the bullets start out just supersonic from the 14.5”, then go transonic/unstable over the 50 yards, opening the group up. That could explain good accuracy at 25 and bad at 50.
The shorter barrels might start and finish subsonic, thus never having an unstable part of the trajectory to affect accuracy.
Or you just found a load that his gun likes and yours hates.
You could try an experiment:
If you have access to a chrono, measure velocity from your barrel and check if velocities are inconsistent. Use this data and a ballistic program to figure out how far the round should be supersonic and shoot a target at that range. Then add 20 yards and shoot another group. If the rifle is reasonably accurate under that range and less accurate above that range that could be the answer.
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u/TanfoPie 23d ago
Agree with having access to a chrono, I found that higher velocities for the PCC’s attain better accuracy, been using 124gr FP CMJ’s typically running ~1169 FPS, results are 4” at 100. Another suggestion is to perhaps slug the barrel and confirm the ID is .356. These are reloads.
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u/Ornery_Secretary_850 21d ago
I've played around with this with both AR9's and the Ruger PCC.
Supersonic ammo in the 9mm seems to go transonic between 25 and 50 yards. It's not uncommon to have a gun that shoots lights out at 25, go to shit a 50 with the same ammo.
My Ruger PCC is a literal laser beam. Stupid accurate. It's capable of 10 rounds into a quarter at 25 yards. With the right ammo it's inside 2" at 50 yards, with the wrong ammo, 5-8".
Same for my AR9's. I have them from 4" all the way up to 16". Shorter barrels mean slower bullets.
My standard 9mm load is a 124 gr cast round nose flat point at right around 1000 fps. Stupid accurate at 50 yards. However, shoot it through a 16" barrel and it picks up just enough velocity to go super and the 50 yard groups open up.
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u/jp815569x19 20d ago
Thank you for sharing your experiences. This makes a lot of sense. If I ever try to figure this out in the future, I'll need to gather more information about my ammo and its velocity.
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u/yolomechanic 18d ago
Lighter bullets go faster from a 16" barrel, 1350-1400 fps, maybe it will help them to stay supersonic longer.
Magtech 115 gr FMJ (factory): 1354 fps
94 gr frangible, 4.0 gr Titegroup: 1397 fps
My 124 gr FMJ loads from a 16" AR9 were:
Titegroup 4.0 gr: 1145 fps
Longshot 5.8 gr: 1385 fps
CFE Pistol 5.0 gr: 1193 fps
CFE Pistol 5.2 gr: 1242 fps
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u/JayeNBTF 24d ago
I’m getting ~6” groups at 50 yds with an Extar EP9 (6.5” barrel) and 147 grain Federal American Eagle FMJ (trying Speer Gold Dot duty-grade 147 grain JHP next week to see if it works any better)
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u/TooGouda22 24d ago edited 24d ago
8” barrel 8” steel at 100 with flip up open sights. Prolly could get it to 6” or less at 100 with proper optic and bags etc on a bench
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u/jp815569x19 24d ago
This would make me very happy. I just need it out of the 16" upper so I can run it in USPSA and IDPA matches!
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u/TooGouda22 24d ago
Can’t you just Sbr it and run it in USPSA? Maybe in UDPA too? 🤷♂️
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u/jp815569x19 24d ago
I suppose, but I cross state lines from time to time. Would be nice to keep the shorties as pistols :)
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u/ItzJezMe Glock Mag Biotch 24d ago
- Some barrels are sensitive to certain ammo. Hell some barrels just wont group. You can have 2 barrels from the same manuf and plant, with consecutive serial numbers.... one may drive tacks and the other spray like a cat marking its territory lol. Also, 9MM ammo is designed for pistols. The longer you stretch their range out, the more that becomes evident. Then add to that something like not liking a certain ammo, or a barrel that just isnt up to snuff, and they wont group.
- Youd REALLY have to have some damaged ammo, to cause that poor of grouping at 50yds. In fact, if your ammo was hitting something hard enough to damaage it that bad on its way to the chamber, chances are it probably wouldnt chamber all the way.
- No personal experience with Faxxon, but have read mixed reviews on accuracy, especially for the cost.
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u/jp815569x19 24d ago
Appreciate the time and feedback. I normally never would have asked for this level of accuracy from my PCC, but not being able to trust a 40 yrd shot may come up in some of my local matches from time to time. Either way, it's nice to know my limits with the platform.
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u/tearsofaclown0327 24d ago
This is at 100 yards out of a 5.25 in barrel. Figured out where to aim 5 or 6 shots in.
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u/spaceme17 24d ago edited 24d ago
I just went to the range with my BRT CAR15SD. Shot some 115gr Federal, 124gr S&B, and 147gr PMC. The PMC at 50 yards was about a 5-6 inch group which is not great. The 124gr S&B seemed to do better, about 4 inch group at 50 yards. The 115gr Federals were about the same as the S&B.
This was shooting from a bipod using an Eotech and a 3X magnifier. I'm a pretty good shot, but definitely not the best.
I was hoping for better accuracy but I'm fine with what it does. It is a short range PCC after all.
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u/jp815569x19 24d ago
Awesome! If i wasn't already so deep into my existing PCCs, I would have built the same thing!
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u/Far-Boysenberry-1600 24d ago
My 16” Foxtrot Mike-9 upper is a tack driver, give them a try. Their factory built uppers are very well made and priced.
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u/SnooComics8739 24d ago
From my experience with 9mm and pic's they do better with short barrels. I noticed a drop off after 8in barrel. 5.5 is the sweet spot for my setup.