Twist rates and bullet weights. Hit me with some knowledge.

[Lebowski]

Now that I've got a decent place near me to shoot some longer distances, I'm wanting to try to reach out and touch some steel at 100, 200, 300+ yards. I'll probably be swapping the cheap JSE 16" barrel on my original AR build and keeping it for a future project, to replace it with a 20" 'better' barrel for some longer range pllinking with 223/556 since it's a cheap round.

Question is: What should I be looking at in regards to twist rates and bullet weights for some longer distance shooting. I have a nearby range with targets out to 500 yards but with the optics I currently have I'm lucky to see the targets at 300yards. What would be a good combo?

 

[hammerd13]

Many on this forum know much more than I about this topic...but I'll give you some info that might help.

The effects of wind and temperature gradients grow more significant on your POI as distance increases. To counteract this, you want a heavier round to "buck" the wind and other thermal influences. Most folks shooting competitively at 500-600 yards are using rounds in the 77-80 grain ballpark for this reason. For a round this heavy to have a stable flight path, you must spin it faster than a ligher round (e.g. a 55 grain). You'll find most distance shooters (service rifle competitors for example), usually run a 1:7 twist...sometimes, but less often a 1:8.

I recently built a Service Rifle and went with a White Oaks Armament 1:7 barrel so that I can shoot more effectively out at 500 yards with a 77 grain Sierra Match BTHP. I can still shoot the lighter rounds with this barrel.

 

[MCgrease08]

I just asked a similar question yesterday.

https://www.indianagunowners.com/forums/long-guns/419534-18-spr-build-1-7-vs-1-8-twist-rate.html

 

[avboiler11]

Contrary to what you might read on the internet...a 77gr SMK will be stable in a 1:9 barrel, even down at sea level with temperatures below 32F.

That said, if you are replacing your AR barrel, I would recommend a 1:8 (or 1:7) twist for additional stability margin with 77gr bullets, which are (generally speaking) the heaviest/best BC bullets one can load to mag feed in an AR. You could certainly single-feed 80s or even 90gr VLDs, but IMO that kind of defeats the purpose of a semi-auto gas gun for all purposes except service rifle competition.

For 300 yards, you could use M193 and not be out THAT much ballistically compared to hand-rolled 69-77s.

You won't "need" a 20" barrel for 500 yards; a 16" would do just fine for that distance. I have a 18" 1:8 rifle gas barrel by BHW and get 2740fps with a 77gr over 8208XBR...it is almost boringly reliable on a 8" round plate @ 650yd.

 

[mammynun]

IMO as long as your bullet remains supersonic at the target distance barrel length is largely irrelevant, so I'd not be in a hurry to replace a 16" barrel for a 20". You'll only be gaining about 200fps with a 20" vs a 16". That said, 200fps will likely have more effect for distances of less than 1k yards than the difference between 1:7, 1:8, or a 1:9 barrel. I'd suggest shooting what you have until you can clearly articulate why you need a different barrel, unless you just want something different. I want something different all the time... so that's reason enough for me.

 

[MohawkSlim]

300 yards is AK with canted sights and Tula off the Walmart shelf distance.

Don't sweat the details. Just shoot!

 

[Small's]

Im running a 1:7 twist chf lightweight 16" barrel with a 1-4x scope that shoots 75 gr gold dots really well and the AE 50gr varmint tipped ammo. Most people say a 1:7 wont shoot well with light ammo. Not exactly true. I sighted mine in at 100yds and had 4 shots around an 1". I thought maybe i just got lucky but the next time i went out i put 5 shots just under one and 7/8" @ 200yards. Ive shot it out to almost 500 yards and it still does really well. Same gun shoots xm193 2-4moa. Bullet quality seems to be more important.

 

[natdscott]

Call White Oak Armory or Keystone Accuracy, and get a 20" 1-7" twist barrel ordered. Wylde chamber is fine. Rifle gas.

Get a 500-count box of the 77 SMK on the way, along with a 5-lb can of Reloder-15, and 5,000 count of either Remington of CCI BR small rifle primers.

Put the Sierras in front of 23.0-24.0 grains of the RE-15, seat it to 2.250-2.255" COAL, in a Winchester or Lake City casing.


And that's about it. Good for 3/4 MOA or better, at 600 yards or under.

-Nate

 

[natdscott]

Contrary to what you might read on the internet...a 77gr SMK will be stable in a 1:9 barrel, even down at sea level with temperatures below 32F

Not bloody likely in a 16" tube. Not even a GOOD idea in 20". And I can tell you that 16" barrels are at a noted disadvantage at 600 yards; watched guys try it, beaten them to death.

I'm not "the internet" saying this, either.

But I should mention, to the OP, that the rest of the avboiler person's post is pretty solid.

-Nate

 

[MCgrease08]

Here is the upper I just ordered today to go with my INGO lower SPR build. It seems like a pretty nice package at a good price.

PSA 18" Rifle Length 223 Wylde 1/7 SS 15" M-Lok Upper - with BCG and CH - 7792389

 

[avboiler11]

Not bloody likely in a 16" tube. Not even a GOOD idea in 20". And I can tell you that 16" barrels are at a noted disadvantage at 600 yards; watched guys try it, beaten them to death.

77gr SMK @ 0.994" OAL
2350fps (10.5" velocity)
0' ASL elevation
20F temp

Stability factor of 1.21 through a 1:9 barrel.

That's considered 'marginal' stability, but anything 1.00 is considered 'stable' with 1.40 'fully stable'. That isn't to say such a bullet would be most accurate in an given barrel...but a true 1:9 twist will cut round holes.

I previously owned a Savage 12FV (26" 1:9 twist bolt action) that shot 10-round, 0.8 MOA groups @ 200 yards with a 75gr Amax...and on that day, even with velocity north of 2900fps, its stability factor was exactly 1.00. Holes were cut perfectly round, not a hint of keyholing.

 

[natdscott]

Sure, avboiler, I can do math too. Have a lot of times in fact, when making choices for bullets and barrels to try to compete head-to-head with my Service Rifle against all match rifle shooters (who are unlimited, basically), and beat them....seeing as we all compete for the same prizes.

The guy was looking for reliable advice, so I say: any bullet that will only stabilize to 1.21 is a bad choice for that rifle, and if a guy HAS to shoot that bullet, then he needs to "suck it up buttercup", and get a barrel for the purpose. Call somebody like Brian Litz and see what he thinks about it.

TRUST me, I have. I ran the 82 Berger to a US Distinguished Badge, even though it was really only marginally stabilized by the 8-twist I had at the time...what it meant was that I had to push components harder, and the brass lasted at least 2 shots fewer firings. Keep in mind...the guy's asking about an AR.

My advice is based on a lot of success regionally and nationally on my own, but what's really a lot more, it is based on the collective choices and wisdom of tens of thousands of competitive shooters AND the US Military, who all agree that a 9-twist is just too loose, and that the 70-series bullets need more--as a rule (not a guideline)--to be stable in the variety of conditions we shoot in on this little planet.

I'll go one further: the 9-twist .223 Remington barrel is the WORST twist rate commonly in use. It's too slow for fast, and too fast for slow. Can't run heavies, but a little faster than needed for short varmint and BR bullets.

-Nate

 

[avboiler11]

I certainly wouldn't sling up and compete with 77s in a 1:9 barrel...but for a recreational shooter wanting to bang steel or punch paper, there's something to be said for "run what ya brung" when it'll still work for those particular uses.

I agree with matching a barrel to a bullet (as I said, my FrankenSPR has a 1:8), but a box of bullets is cheap compared to the cost of a new barrel so why not try some and see how they work in the existing barrel before making that investment? He might be pleasantly surprised.

I agree 100% that 1:8 would be a much 'better' twist rate for factory 223 rifles than 1:9...it would work better with 77s and be suitable for 75/80 VLDs while still doing great with 55 FMJBTs.

 

[Lebowski]

Thanks fellas. I understand the concept of 'run what ya brung', but since I bought a completed AR upper off of GunBroker, with an unknown twist rate for my first build (which I am now trying to optimize a bit for better accuracy) I figured I'd replace the barrel and trigger on it. With a red dot / irons I can reach out to 200yds with cheap surplus ammo but I've not got great optics to even see beyond that.

 

[sgreen3]

Here is a good resource for the cartridge with some info on twist rates. 223 Rem + 223 AI Cartridge Guide

 

[mammynun]

with an unknown twist rate

You can put a mark on a cleaning rod (parallel with the bore) with a patch, pull it slowly down the bore, and measure the distance that the rod travelled to make the mark rotate 360 degrees. Repeat as necessary till you're confident of your measurements.

Are you sure the twist isn't stamped into the barrel somewhere?