Against the Grain! Shooting 75-77gr rounds in 1/9 AR upper

[Samurai FI]

Could those of you who have shot 75 grain - 77 grain .223s through 1/9 twist 16" AR inform me if the rounds stabilized or did not. And please include what brand of ammo and AR.

Most know that the 1/9 twist is less than optimal for heavier grain .223s, but there are always exceptions. I am especially interested in hearing if someone has shot prvi partisan 75gr match or black hills 75gr match through a 16" Stag.

Thanks

 

[Slamfire]

I do not shoot heavy bullets through a 1:9. However a bud of mine has a Space Gun upper with a 1:9 twist. He shot 75 grain A-Max bullets out to 600 yards and shot scores in the lower 190's with it. I had told him that a 1:9 would not stablize anything heavier than a 69, and I was wrong.

I have seen examples of 1:9 twist barrels that would not shoot 75, 77 grain bullets, and I mean huge blown groups. But I guess there are the rare examples that will.

Just loads some groups and see what happens.

 

[Samurai FI]

thanks,
I plan to once the temp get back into double digits.

 

[LeonCarr]

I shoot 75 grain Hornady BTHP (not the A-Max but the regular BTHP) through a 1/9 twist Bushmaster M4orgery and get 1.25 inch three shot groups at 100 yards. Not quite as tight as 55-69 grain loads, but good enough I guess .

I have heard if your rifling twist isn't fast enough to stabilize, your groups are WAY bigger than 1.25 inches .

Just my .02,
LeonCarr

 

[Soybomb]

You should probably ask for distances and maybe temperature too. What might be stable enough for 50 yards might be making key holes at 100 or 150. What works for a guy in the desert might not work for the person shooting in snow.

 

[Conqueror]

I'd be more comfortable running 69grs through a 1-9. I've never run 75/77 through a barrel that "loose."

 

[rbernie]

You should probably ask for distances and maybe temperature too. What might be stable enough for 50 yards might be making key holes at 100 or 150. What works for a guy in the desert might not work for the person shooting in snow.

Excellent point - the colder the weather, the faster the bullet needs to spin to stabilize.

I've shot 75gr Hornady BTHP handloads (muzzle velocity ~2700fps) from a 16" 1:9" Armalite barrel and they were stable and just about MOA at 100 yards, in temps ranging from 110F to about 45F.

 

[silverlance]

Hm. so let me get this right:

1-7 : use 55gr
1-9 : use 62

is that right?

 

[rbernie]

1-7" : optimum for 69gr-75gr, can shoot lighter
1-9" : optimum for 55gr-69gr, can shoot lighter
1-12" : use 55gr or less

 

[ugaarguy]

I am especially interested in hearing if someone has shot prvi partisan 75gr match or black hills 75gr match through a 16" Stag.

Well, you've peaked my curiosity. With help from a co-worker I've recently assembled a 20" 1:9 flat top upper from parts traded in at the shop. We recently got in some of the Prvi Partisan (packaged as Wolf Gold) 75gr match. I'll have to buy a box and run it through the franken-upper to see what it does. Of interesting note my 1:12 20" SP1 upper has shot some fairly decent groups with 62gr JHP Remington green box ammo in the past. Some range ti.. err.. I mean ...research is in order.

 

[Bartholomew Roberts]

All groups are 5rd groups.

Bushmaster chrome-lined 16" HBAR 1:9 using 75gr BH Red and Blue, 75gr Hornady TAP, and 77gr Mk262 Mod 0 - 4-5" at 100yds, around 10-20" by 200yds. This same rifle would tighten up and occasionally produce match like accuracy in the summer when it got warm; but not consistently.

Bushmaster chrome-lined 16" HBAR 1:9 using 75gr BH Blue - 4-5" at 100yds.

Bushmaster chrome-lined 16" M4 1:9 using 75gr BH Blue - 4-5" at 100yds.

Armalite 16" chrome-lined HBAR 1:9 using 75gr BH Blue and 75gr Hornady TAP - 1-1.5" at 100yds.

 

[GJgo]

My recommendation would be to use the "standard" that everyone recommends only if you don't want to do some testing of your own. As I'm sure you've also heard, every rifle will behave a little differently.

I tried Nosler 55gr ballistic tips, 69gr SMKs, 75gr Hornady BTHP, and 75gr Hornady A-Max. I tried Varget and H335. I loaded them for my Savage 26" 12VSS .223 1:9, my RRA 16" CAR-A4, and my friend's Bushmaster 20" Predator 1:8. I've shot them wen it's 100 degrees out and more recently when it's in the 20s and 30s.

All rounds "stabilized" in all rifles. However, there were large discrepancies in accuracy. In none of them were either of the 75 grainers what I'd call good. In other words, I would never want to put them downrange at a target that actually meant something. In the Savage, the 55s were great and the 69s were good. In the RRA and the Bushmaster, the 55s and 69s are both great. Heck, that Bushmaster shoots half inch groups with M855!

YMMV, and of course, we'd like to hear what it is.

 

[vanilla_gorilla]

Remember, some 1:9s will stabilize the 75-77s and some will not. The best way to determine is to take YOUR rifle and shoot them and see.

 

[jaholder1971]

1:9 _should_ stabilize a bullet up to 75 grains, provided you keep the velocity up. In a 20-24" barrel, no problem, in the carbines I dunno, never owned one.

1:8 will stabilize a bullet up to an 80 grain Sierra Matchking. It's about the most popular twist rate for NRA highpower for those shooting an AR.

1:7 is the original M16A2 twist rate, will stabilize all 80 grain bullets including the VLD designs.

1:6.5 is required if you're shooting those long, nasty looking 90 grain Sierra's.

 

[Dobe]

What kind of decrease in barrel life exist as the rate of twist increases?

 

[Hypnogator]

jaholder, you pretty much answered the question I posed in another thread on twist rates. Does anyone have experience with stabilizing 55 - 80-gr bullets in a 1:8 barrel?

 

[jaholder1971]

jaholder, you pretty much answered the question I posed in another thread on twist rates. Does anyone have experience with stabilizing 55 - 80-gr bullets in a 1:8 barrel?

My Eagle Arms EA15 sported a 1:7 before I replaced it with a 1:8 Golden Eagle barrel. I shot plenty of 55 grain HPBT's and Ballistic Tips through that 1:8 in 100 yard matches and plenty of 200 yard standing and sitting stages.

I only switched to 77's because shooting the same bullet across the course made reloading simpler.