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6/25/2018 7:04:05 PM
Posted: 3/22/2018 4:30:42 PM EDT
[Last Edit: 4/13/2018 11:32:06 AM EDT by mcantu]
Finally got a chance to try out my new 16", 1:7 twist AUG barrel compared to the 20", 1:9 barrel on my A1. I was really curious how the poi would change between the two.

Ammo was MEN M193

20" @ 50yds


16" @ 50yds


20" @ 100yds


16" @ 100yds (wtf)


I was definitely not expecting the 16" to be shooting higher. It also felt like it shot softer than the 20", which makes no sense. Ejection was @ 3 o'clock with the 20" and 5 o'clock with the 16"
Link Posted: 3/22/2018 4:55:25 PM EDT
I would be interesting in knowing how much shift there is from when take off and reinstall each barrel.
Link Posted: 3/22/2018 5:01:25 PM EDT
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Originally Posted By dcs12345:
I would be interesting in knowing how much shift there is from when take off and reinstall each barrel.
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None
Link Posted: 3/22/2018 7:33:31 PM EDT
Just measured. Going to the 16" barrel moved the poi 3.5" up and 1.5" left @ 50yds
Link Posted: 3/22/2018 9:25:44 PM EDT
Once I get some time, I've been meaning to go to a local 100 yard indoor range and test POI from swapping between four different 24" barrels.

My brother has an AUG and swapped his 16" barrel to his new 24" barrel at 100 yards and wasn't even on paper without rezeroing to the 24" - so I don't think your 20" to 16" deviation is so bad. At least you were on paper...
Link Posted: 3/22/2018 9:26:39 PM EDT
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Originally Posted By mcantu:
None
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Originally Posted By mcantu:
Originally Posted By dcs12345:
I would be interesting in knowing how much shift there is from when take off and reinstall each barrel.
None
I'll second that.
Link Posted: 3/22/2018 9:55:02 PM EDT
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Originally Posted By maleante:
Once I get some time, I've been meaning to go to a local 100 yard indoor range and test POI from swapping between four different 24" barrels.

My brother has an AUG and swapped his 16" barrel to his new 24" barrel at 100 yards and wasn't even on paper without rezeroing to the 24" - so I don't think your 20" to 16" deviation is so bad. At least you were on paper...
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Well, only half of the 16" shots @ 100yds stayed on paper

Next time I'm gonna try with some 62gr stuff.

Thinking about it more, it could be that the reason that the 16" felt like it was shooting softer was because of the tulip flashhider. The 3 prong FH on the A1 probably isn't as effective at reducing felt recoil. I wonder if Pete has any A2 flashhiders in stock?
Link Posted: 3/22/2018 10:57:51 PM EDT
If you don't care about the new wrench flat style tulip FH, I'll send you one. Let me know.
Link Posted: 3/22/2018 11:08:04 PM EDT
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Originally Posted By maleante:
If you don't care about the new wrench flat style tulip FH, I'll send you one. Let me know.
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Will that work with a hex checknut? I'd really want to keep the aesthetics of the A1/A2
Link Posted: 3/23/2018 12:16:57 AM EDT
Neat test, thanks for posting.
Link Posted: 3/23/2018 12:24:57 AM EDT
Originally Posted By mcantu:

I was definitely not expecting the 16" to be shooting higher. It also felt like it shot softer than the 20", which makes no sense.
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You think anybody is able to make removable barrels and have them all with the same exact alignment?

POI shift is about alignment shift between barrels, not change in MV of the bullets.
Link Posted: 3/23/2018 8:40:53 AM EDT
It'll look exactly like the new STG77. Not preban original, but close.
Link Posted: 3/24/2018 10:52:17 AM EDT
At first it looked like the 16" grouped better, at 50 yds but spread out at 100.

Understood on the tulip vs 3 prong. I'll have to find/load 62s for my own test.

Thanks mcantu for the posting and pics.
Link Posted: 3/24/2018 1:32:24 PM EDT
The bullet is still going UP at 50 yards, if you start out there when zeroing it will be HIGH at 100.
I ZERO at 100 and all my rifles are about 1/2"-1" low at 50 and hit on target at 100
The 1/7 will start to scatter 55 grain bullets at 100 because they are over rotating in that twist. I have a Colt LE 6940 that is very accurate at 50 with 55 grain it starts to really spread at 100. You need to shoot 62 grain on UP to 77 grain it will shoot great
Link Posted: 3/24/2018 2:26:04 PM EDT
[Last Edit: 3/24/2018 2:27:20 PM EDT by Kali_Refugee]
Bullets don’t defy gravity and rise on their own that’s all based on your zero. Gravity doesn’t discriminate.

https://www.ar15.com/forums/ar-15/Argument__Does_a_bullet_rise_out_of_the_barrel_/118-257820/

Plus mythbuster plus plenty of other sources dispelling that with equations if you google it.

I don’t think you are right about the twist rate and projectile weight in this instance either. Molon did some great posts on stuff that are archieved.

https://www.ar15.com/forums/ar-15/1_7_vs_1_9_accuracy_with_XM193__/118-669894/?

OP if you had more than one group it would be more interesting single 10 shot groups don’t really show much.
Link Posted: 3/24/2018 4:16:39 PM EDT
[Last Edit: 3/24/2018 4:18:42 PM EDT by mcantu]
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By OldShelbyGuy:
The bullet is still going UP at 50 yards, if you start out there when zeroing it will be HIGH at 100.
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I get that. This was just to see what the difference in poi would be when changing barrel length. This AUG, with the 20" barrel, is zero'd at 200yds with Mk318 so it's about 2" high at 100yds
Link Posted: 3/25/2018 6:46:54 AM EDT
Mine, switching to a 20" 1/7 from the factory 16", dropped around 4 inches at 50 yards....windage was dead on; it dropped straight down.
Link Posted: 4/5/2018 3:00:40 PM EDT
I took the FN 16" 1:7 barrel out today to rezero with Mk318. Now maybe I was having an off day but every group I shot was 2-3x larger than what I usually shoot with the pre-ban Austrian 20" 1:9. I shot Mk318, CBC Mk262 and RUAG SS109 (which is supposed to be super accurate) and it was the same for each
Link Posted: 4/12/2018 6:55:21 PM EDT
[Last Edit: 4/12/2018 6:55:45 PM EDT by mcantu]
Ok, I'm starting to think that I got a bad barrel. I took the 16", 1:7 barrel out again today to shoot some rounds that I had already shot out of the 20". It's shooting groups about twice as large as the 20" with the same ammo. Today I tried CBC 62gr and ADI F1 (SS109). The CBC was shooting 5" and 6" groups. With the ADI I shot 4", 4 1/2" and 3 7/16" groups. Previously this is how the ADI shot from the 20"...

https://www.ar15.com/forums/ar-15/Foreign_SS109_Variants_Test/16-679478/

Also, if you look at the pics at the top of this thread, look at the 16" barrel groups and you will see that the holes are not perfectly round. On many of them, there is a weird tear in the target coming off of one side of the bullet holes. Could there maybe be a burr in the barrel that is messing up the bullets?
Link Posted: 4/12/2018 9:15:48 PM EDT
[Last Edit: 4/12/2018 9:37:22 PM EDT by doty_soty]
I feel like any measured POI difference would be 99% the summation of the manufacturing tolerances of the individual barrel and its attachment points, and 1% the velocity difference between the different barrel lengths. If a manufacturer can make barrels that all hit to the same POI upon installation, it would be an engineering marvel. Am I missing something?
Link Posted: 4/12/2018 9:36:04 PM EDT
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By OldShelbyGuy:
The bullet is still going UP at 50 yards, if you start out there when zeroing it will be HIGH at 100.
I ZERO at 100 and all my rifles are about 1/2"-1" low at 50 and hit on target at 100
The 1/7 will start to scatter 55 grain bullets at 100 because they are over rotating in that twist. I have a Colt LE 6940 that is very accurate at 50 with 55 grain it starts to really spread at 100. You need to shoot 62 grain on UP to 77 grain it will shoot great
View Quote
Bullets begin to drop the second they leave the barrel, unless your bullets are generating lift.
Link Posted: 4/12/2018 9:38:03 PM EDT
Discussion ForumsJump to Quoted PostQuote History
Originally Posted By doty_soty:
I feel like any measured POI difference would be 99% the added manufacturing tolerances of the individual barrel and its attachment points, and 1% the velocity difference between the different barrel lengths. If a manufacturer can make barrels that all hit to the same POI upon installation, it would be an engineering marvel. Am I missing something?
View Quote
The poi thing was just something interesting to see. Poi will shift with different barrel lengths, different harmonics, even different lots of the same ammo.

My concern now is that the accuracy of this new US made, FN 16" 1:7 barrel is nowhere near that of my 25 year old, Austrian made 20" barrel with thousands of rounds through it
Link Posted: 4/13/2018 12:17:52 AM EDT
The groups you’re getting do sound pretty darn big considering the ammo being used, and that you’re getting good groups with other setups as linked. I’d wonder if there’s a burr or something in the barrel, the crown is damaged, or if something is wonky where it locks into the receiver.
Link Posted: 4/13/2018 9:24:46 AM EDT
btw, these are the #'s for the group in the OP with the MEN M193 from the 20" barrel

Link Posted: 4/13/2018 2:21:12 PM EDT
The holes dont appear to be keyholes, so here's my hypothesis: the jackets at the base of those bullets are separating. This would certainly throw your accuracy to shit, and explain the flower petal holes youre getting with that ammo.
Link Posted: 4/16/2018 7:46:00 PM EDT
I talked to Herbert at Steyr today. The barrel is going back for them to check out
Link Posted: 4/20/2018 12:18:00 PM EDT
I've gone back to the 20" pre-ban barrel for now and all is right with the world again...

https://www.ar15.com/forums/AR-15/RUAG-HC-SS109-Range-Report/16-726682/
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