Build Thread Problem with a new ar15 barrel

[BlackSheepJ]

So I'm hoping someone smarter than me can help with a problem I'm having. Just assembled a new rifle, using a 14.5" 1 in 8 twist polygonal 223 wylde barrel. Figured that would stabilize just about anything I wanted to shoot. Rifle has a pinned precision armament Efab, 1x6 trijicon optic and a 3.5lb triggertech. I was shooting off a bench at 100 yds.

Well, I am not seeing keyholing, but when I tried two different 75gr loads I got some fairly extreme spreading. One was 75 gr Speer Gold Dot .223, the other was Hornady frontier 75 gr OTM 5.56. Accuracy was abysmal with both, with odd vertical and horizontal stringing.

I have other barrels with a 1 in 8 twist that shoot both those loads fine, my 1 in 7s as well. I had some swede 62 gr 5.56 that I shot as well, which is the only one that turned in a group. I zeroed the gun a few weeks ago, with the 75 gr frontier and didn't notice a problem, seemed to group fine. It only has maybe 100 rounds through it.

Did I just get a picky barrel or is this normal performance for a 1x8? Did I get lucky with my other 1x8s? I have no idea why it's shooting so poorly.

Any and all advice or ridicule is welcomed, just want to figure out a solution.

Thanks for any help.

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[bbbass]

My 18.5" 223 Wylde 1/8 shoots 52gr, 55gr, and 62gr to dime sized 5shot groups at 100yds. Have never shot heavier loadings in it.

Gonna have to get help from someone smarter than me...

 

[BlackSheepJ]

My 18.5" 223 Wylde 1/8 shoots 52gr, 55gr, and 62gr to dime sized 5shot groups at 100yds. Have never shot heavier loadings in it.

Gonna have to get help from someone smarter than me...

If I'm stuck with lighter projectiles, that would be fine, just wish I knew why this particular barrel is being a problem child. Thanks for the reply.

 

[bbbass]

i hope u get yor answer!

 

[Medic!]

It's not just twist rate.
It's also barrel length.

A longer barrel will give you more velocity. And spin a bullet at a higher RPM.

Also. I know that bullet weight is what we always talk about .
But length is what determines the needed RPM/spin rate.

 

[slimmer13]

What's the barrel?

 

[v0lcom13sn0w]

who makes the barrel?

 

[BlackSheepJ]

What's the barrel?

who makes the barrel?

Columbia River Arms, used to be BlackHole Weaponry.

 

[slimmer13]

Columbia River Arms, used to be BlackHole Weaponry.

I have had a couple of their barrels. They shot well. IIRC, they recommend a break in to uniformly gild the barrel with copper. Not sure how much of a difference it makes.

 

[BlackSheepJ]

It's not just twist rate.
It's also barrel length.

A longer barrel will give you more velocity. And spin a bullet at a higher RPM.

Also. I know that bullet weight is what we always talk about .
But length is what determines the needed RPM/spin rate.

My understanding is the Hornady 75 gr loads should work with a 1 in 9 though. Box on the Speer says 1:9 or faster as well. I don't understand why they wouldn't work in this gun.

 

[BlackSheepJ]

I have had a couple of their barrels. They shot well. IIRC, they recommend a break in to uniformly gild the barrel with copper. Not sure how much of a difference it makes.

I followed their break-in. I didn't notice any real difference from the initial range visit with the initial groups though.

 

[v0lcom13sn0w]

that is odd. some barrels just dont like some bullets/bullet weight

 

[BlackSheepJ]

Thanks guys for the help, Medic! said something that stuck with me. Twist rate and barrel length, so I measured the length and used a cleaning rod to measure the twist. Length is right, 14.5 pinned to 16.1ish inches. Twist seems to be a 1x9, even though I ordered a 1x8 and that's what is marked on the barrel. Get to try out customer service tomorrow. Kinda peeved, waited a while for this barrel. I'll check back in when I know something. Thanks everybody. Thanks Medic! wouldn't have even crossed my mind without you speaking up.

 

[Member 34319]

I am not sure @Medic! meant that?

I'm thinking he was referencing the fact you had a 14" barrel over a 20" type thing.

Though it may be a 1/8, that doesn't mean it will properly stabilize longer heavier bullets. Heck even if it is a 1/7 it might not. Especially if the barrel is shorter than its intended length.

For instance. I was trying to find the shortest 300 blackout barrel I could find. 5-6" type thing. Yet no one makes them with a faster twist rate, just the same old common twist rates. Sig uses a 6" barrel in their rattler, but they knew because of the short barrel length, to stabilize large heavier bullets in that length of a barrel, they needed a 1/5 twist rate.

 

[Medic!]

If the goal is to spin a bullet at a certain RPM for stability and best accuracy. Then targeting that Rate of spin will involve twist rate and Velocity.

Let's use 1/12'' because the math is easy.

Different velocities [Barrel lengths] will give different bullet RPM's .
All with the same twist rate.



[Something like this. But these numbers are just off the cuff as an example].



Barrel length. Velocity in FPS [ x60 ] = RPM

14.5'', 2,900 FPS, 174,000 RPM

20'', 3.200 FPS, 192.000 RPM

24'', 3,400 FPS , 204,000 RPM


1/7'' is even more dramatic with the twist rate going up to 1.714 rotations per foot traveled down range.

14.5'', 2,900 FPS, 298,236 RPM,s

20'', 3,200 FPS, 329.088 RPM's

24''. 3,400 FPS. 349.656 RPM,s


If my foggy morning math is correct. [