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 What grain bullet weight do you recommend for 1/9 twist 20" AR barrel?
HermanSnerd  [Team Member]
3/29/2011 6:30:04 PM
From what I have read, with a 1/9" twist barrel, any weight over 68 grain can be iffy as to it's long range accuracy.

I shot my first match with 55grn. Federal XM193 and did ok, but I want to try some better quality ammo.

I don't reload so working up the perfect load in small batches is not an option.

I plan on buying one 50 round box each of Black Hills 55 grn FMJ, 68 grn. match hollow point, 69 grn. Sierra match king, and 60 grn. V-max from Midway USA
and see what my rifle likes best.

Just wondered how many of you guys are shooting a 1/9 AR and what bullet weight you are shooting.

zw123  [Member]
3/29/2011 6:38:44 PM
I have a 1X9 RRA, it's a 16" though. I could not get 69 SMK to shoot exceptional.

I found Sierra 60 grainVvarminters to work extremely well, better than 55's. I never tried over 69 because the 69's were just OK.
bpm990d  [Member]
3/29/2011 6:38:50 PM
Try some Hornady 75 HPBTs. I've shot them in a 9 twist out to 600 yards. They were stable.

B
RedFalconBill  [Team Member]
3/29/2011 7:20:06 PM
Factory loads, I try BH 69gr Sierra MK.

For handloads, either the Sierra MK, the 69gr Nosler, or the 73gr Berger.

panzer  [Team Member]
3/30/2011 9:24:42 AM
Originally Posted By bpm990d:
Try some Hornady 75 HPBTs. I've shot them in a 9 twist out to 600 yards. They were stable.

B


Absolutely. Also the 73 Bergers mentioned.

Ameshawki  [Member]
3/30/2011 4:16:26 PM
My 1 in 9 M4 clone loves 69 gr SMKs.
Garandpa  [Member]
3/30/2011 8:55:18 PM
I've done some load development for my son-in-law who has a 20" 1:9 barrel and found that 69 grain SMK's and also 69 PRVI HPBT match gave good results out to 600 in calm conditions. I didn't try anything heavier, but I've been told that some 1:9 barrels can handle 75 grain bullets and others cannot. Give some a try and see what your rifle likes. Even if its not the best, they might come in handy in a stiff wind at 600.

Roy
ArtD  [Member]
3/31/2011 9:05:49 AM
The Sierra 69 gr. HPBT is approximately 0.897" long. With a velocity of greater then 2800 fps, a 1/10.06876 twist is required. The Hornady 75 gr. BTHP is about 0.995" long and requires a 1/9.077065 twist if velocity is over 2800 fps. In both cases, your 1/9 barrel should stabilize these bullets. The 69 and 75 gr. bullets from Prvi Partizan are actually a little shorter then the Sierra and Hornady bullets I quoted above. So they should also stabilize nicely.

Art
ajroyer  [Member]
5/18/2011 3:40:07 PM
Originally Posted By ArtD:
The Sierra 69 gr. HPBT is approximately 0.897" long. With a velocity of greater then 2800 fps, a 1/10.06876 twist is required. The Hornady 75 gr. BTHP is about 0.995" long and requires a 1/9.077065 twist if velocity is over 2800 fps. In both cases, your 1/9 barrel should stabilize these bullets. The 69 and 75 gr. bullets from Prvi Partizan are actually a little shorter then the Sierra and Hornady bullets I quoted above. So they should also stabilize nicely.

Art


Could you tell me how to find this kind of info? I have a RRA Entry Tactical and I tried using 77gr factory loads. The bullets went through the paper straight (i.e. stable), but the group was much larger and erratic than the 55gr xm193 that I also tried. All this testing was at 200 yds. I had resigned myself to lighter bullets and blamed it some of it on having the shorter barrel and 1:9 twist. How much does barrel length and the cooresponding bullet speed matter compared to the twist rate of the barrel? Is it possible that I could get good, stable flight and tight groups with 69gr factory ammo in my little tactical? If so, why all the data out there about 1:8 and 1:7.7 twists?
bpm990d  [Member]
5/18/2011 5:16:50 PM
Try the Miller Stability Calculator on JBM Ballistics. If you go up a level you can read his paper about twist rate.

Another option if Bryan Litz's book Applied Ballistics for Long Range Shooting. He has the Miller Twist Formula and corrections in spreadsheet format.

B
Gamma762  [Team Member]
5/19/2011 3:31:48 PM
Originally Posted By ajroyer:
If so, why all the data out there about 1:8 and 1:7.7 twists?

Those are the most popular twists for match shooters... the service rifle match types and others go all the way up to the Sierra 80gr bullet which is so long it can't fit in a magazine and must be single loaded through the ejection port. 1:8 is the most popular twist for this usage, Krieger introduced the 1:7.7 to add a little more stability to the 80gr bullets.


Is it possible that I could get good, stable flight and tight groups with 69gr factory ammo in my little tactical?

Absolutely.

Originally Posted By bpm990d:
Try the Miller Stability Calculator on JBM Ballistics. If you go up a level you can read his paper about twist rate.

There's a lot of good info on that website.
ajroyer  [Member]
5/20/2011 12:53:41 PM
Thanks for the info guys. That site is pretty in-depth. It will take me a while to process that much data. I guess my next stop is the range!
captain127  [Member]
5/27/2011 1:12:31 AM
generally speaking if you shoot at actual 600 yard distance the ideas is to use the heaviest bullet your gun will stabilize- that's why all the 1-8 twists and 80 grain bullets being used at 600. !/9 is an iffy twist for shooting heavy bullets at long range-as mentioned above some guns will shoot them well others not so much. and atmospheric conditions (heat /humidity) can take an iffy bullet that shoots ok one one day in a certain weather condtion and see the accuracy fall apart in different weather conditions
Usagi  [Member]
6/16/2011 11:50:18 PM
I have a 1:9 BM barrel (HBAR), and 75-gr Privi is the best load I've tried.
To be fair, I've not tried the 69-gr load, which is supposed to be pretty good, too.

The 75-gr Privi had no issues stabilizing.
I've read that the stabilizing issues for 1:9 barrels are for the 14.5" and 16" (and then, mainly due to velocity) barrels. And as someone else mentioned, the Privi bullet is shorter.
HermanSnerd  [Team Member]
6/17/2011 12:15:26 PM
This past weekend I finally got back out to the High Power range and shot at 300 yards with open sights on my 20" service rifle AR.

I purchased a box of the Black Hills blue box remanufactured 68 grain heavy match hollow points since it was the least expensive
of the heavier Black Hills offerings, and my local shop was out of 69 grain Sierra match kings.

The ammo shot pretty consistent groups, and I need to try it again later with my rifle that has an optical
sight to get a better idea of what this ammo is capable of.

I will report back with some pics when I can.