(cross-posted from the bullpup forum)


Some interesting results today.



100yds, 10rd groups, 1.5x optic, crappy sandbag setup

Pine Valley 77gr 5.56

1:9 Austrian 20"
2.106", mean radius 0.585"
0.923", mean radius 0.352"

1:7 FN 16"
2.518", mean radius 0.794"
2.528", mean radius 0.672"
2.132:, mean radius 0.562"

(16" barrel top groups, 20" barrel lower groups)


RUAG Swiss P 69gr .223

1:9 Austrian 20"
1.286", mean radius 0.399"
1.606", mean radius 0.403"
1.899", mean radius 0.652"

1:7 FN 16"
1.877", mean radius 0.515"
2.073", mean radius 0.662"


(16" barrel top groups, 20" barrel lower groups)



I hot swapped the barrels w/o touching the optic. 16" barrel shoots about 7" higher and 1.5" left of the 20".
Yes, that's sub-moa with 77gr SMKs from a 1:9 twist barrel.
The pre-ban Austrian barrel with untold thousands of rounds through it, out shoots the almost new FN barrel

But, but , but.

ARFCOM says shooting anything bigger than 62gr bullets through a 1/9 twist barrel will tear a hole in the space/time continuim!

Like you OP I tried heavier bullets in my rifle and found out it liked them also.

I was making hits on steel at 600 yards with my 14.5 Bushmaster 1/9 using MK 262 Black Hills 77gr ammo.

Something "Experts" say is almost impossible.

Just goes to show there are no hard and fast rules when it comes to individual firearms and sometimes things get repeated as fact that may not always be correct.

I agree that 77's will work in a 1:9 and that 55's will work in a 1:7 or 1:8.    However, I don't see how shooting two groups with 77's from the 1:9 and claiming sub-moa makes sense.  Based on the average of the two groups 1.5 moa would be more honest... that said, it's pretty good shooting with a 1.5x optic.  Good job, OP.

I usually follow Molon's pattern and shoot 3 groups of 10, but I only had one 50 round box of each and ammo is expensive right now

OP:
Good shooting.....  
Have you verified the twist of the barrels?
In averaging the means you posted:
In the 20"... the 77's averaged at .468 and the 69's were a .484
In the 16"... the 77's averaged at .676 and the 69's were a .588...............

I'd shoot it some more (more groups) before really making any comments though.

Big hunt:
It's good that the OP's rifle shoots the 77's well in a 1/9......
But there are alot of threads of shooters having issues.
So me personally look at the "rule" in shooting 75+ grains in a 1/9 is that it can, potentially, lead to problems.
It's just one of those things to test, like the OP did.  
There are too many variables to make a "rule" about if a 1/9 barrel can shoot 75+ bullets.....

ie In the VERY limited testing the OP did, the 20" barrel seemed to shoot better.......  Is that because it's longer? more worn? Seats better in the receiver? etc?  
Does that mean if I shot it in a 14.5" or something, I'd get poor results?  
Or a 10"....... would it even stabilize?        

Good points.
The 20" is definitely 1:9 because all Steyr AUG preban guns were 1:9.  The 16" FN 1:7 I bought direct from Steyr

Ok, so you haven't verified the twist.  
What most do is take a rotating cleaning rod like a Dewey and a tight fitting brush or swab and see what the twist actually is.
Also there are 1/7" 20" barrels out there IIRC.    

I've had the AUG since 1995 and it was made in the 80s. I've never heard of 20" barrels being 1:7 that far back. I'll try the cleaning rod thing though

He might not be saying it's a 1/7, but some 1/9 marked barrels actually are closer to 1/8 or 1/8.5 twist.  My S&W 1/9 is closer to 1/8.5 and likes 75gr pills.  Another thing is that at 100 yds it might not matter if they're not completely stabilized but at 300+ it could make a big difference

OP:
I apologize if I wasn't clear.......  I didn't know (or Ask) and you didn't mention that you'd owned the AUG for that long and that was the original barrel.  
Since then (the 80's) there have been (IIRC) 1/7 20" barrels made.
I wasnt sure if you had one of those............

Otherwise if we are wandering down this road........IMHO..... for this test to mean anything, then you should verify the twist.....
since, yes as Dogue points out (atleast with some AR barrels) the actual twist maybe different from the published...... (which is my question)  
   

#1 Great shooting OP
#2 The older barrel may be broken-in while the newer one may not be yet.
#3 Never assume anything. I doubt any gun is exactly 1:9 or 1:7 etc
#4 I need to get an AUG somehow