Looking for an ar

[Ohiobellboy]

So I figured I'd jump on the bandwagon before the price goes flying up again. I'm just starting to look and can't really decide if I want to attempt to build one or just go buy one. Seems like the Ruger AR556 and the S&W M&P Sport II can both be had for around $600. Both have Lifetime warranties. Ruger has the 1/8 vs the 1/9 twist barrel in the M&P. Won't be doing anything special with the gun other than occasional plinking with it.


Let's hear some thoughts guys. Armslist and FB have crazy stupid prices on used ones right now. I'm seeing ATI Omnis that sell for around $450 that guys are asking $600 for them

 

[~ZENAS~]

Twist rate has been nothing but empty speak in my experience. My Colt 6940 has a 1:7 rate and can easily shoot very short/light bullets with no effects of too much spin. And I have a bushmaster with a 1:9 twist that I set up for long range and it is a tack driver with 75 grain Hornady match bullets out to 600 yards all day long. I wouldn't let twist rate factor in much at all to your choice. Most of the talk is just people running their mouths on the internet.

 

[RangerTim]

1:8 or 1:9 would be fine for general use. Every rifle barrel is different. I've seen two identical 1:7 Colt's where one shot 55gr fine and the other wouldn't group it worth a damn. My DD M4A1 SOCOM is a 1:7 and it shoots everything from 55gr - 77gr without issues. Damn near identical POI with everything in between as well. I have had a M&P 15T for 10 years or so (right after they came out) and it has been an absolutely awesome rifle. Had an M&P 15TS for a few years that was also fantastic. For the money, I'd take the M&P rifles every time. I'll caveat that with both the "T" and "TS" are top end M&P rifles. While I don't have as much personal time behind the trigger on the Sport or other lower end models, we use them as loaner/rental rifles for a 3 day tac rifle class one of the places I instruct and they run/shoot great.

 

[~ZENAS~]

[QUOTE="Chris Timmerman]1:8 or 1:9 would be fine for general use. Every rifle barrel is different. I've seen two identical 1:7 Colt's where one shot 55gr fine and the other wouldn't group it worth a damn.

[/QUOTE]
But are you sure that's attributable to the twist rate? I think many times a poor shooting barrel gets put on twist rate with no real proof that's the problem. When in reality, big groups are likely a completely different issue altogether.


Based on bullet physics, wide group spreads isn't really what the result of twist rate issues causes. A barrel with too slow a twist for the length of bullet will result in a projectile that isn't fully stabilized in flight, meaning it wobbles. So with that, you may have bigger groups, but the real issue will be a bullet that isn't on a straight trajectory and will see "keyhole" shaped holes on the paper down range. But for "overstabilizing" (I use that term loosely since you can't really overstabilize a bullet) caused by a faster twist rate than necessary, the result will possibly be bullets torn apart (jackets spun from the core, or for lead bullets, fragmentation/disintegration). The result won't be larger groups because the flight will still be true since the bullet is stable in flight (just spinning faster than the bullet can handle).


So with that in mind, larger groups, or inconsistent groups, are likely the result of a different problem with the barrel and just falsely attributed to twist rate. The fact is, twist rate and bullet stabilization are an exact science. If a 55 grain bullet of the same length is stable at a 1:7 rate in one barrel, it will be stable in any barrel at that rate. The reason one barrel shoots better is therefore not an issue of twist rate. It is likely an inconsistency in the bore itself. A good example is with chrome lined barrels, the process for getting the chrome plating to adhere to the bore can result in inconsistent thicknesses of chrome in various spots inside the barrel. This will result in inconsistent and larger groups and is likely the culprit in variation between 2 different barrels of the same twist rate with the same length bullet.

 

[RangerTim]

I would agree T.L. that variances in individual barrels are definitely an impact on how a rifle groups specific bullets. It was interesting though when that Colt I referenced above that wouldn't group with 55gr was a hammer with 62gr or heavier. If the larger determining factor was variances in the barrel such as non-uniform chrome lining I would expect it to have the same impact on any bullet weight. I by no means am an expert however. While I do help instruct precision rifle classes I am not the ballistics guru among the instructors. We have another guy that could teach a college level course on ballistics.


I look at it this way too, if a barrel with too slow a twist for a heavy bullet fails to stabilize the bullet in flight, much like a loose and sloppy spiral on a football pass, how likely is that football to hit that pinpoint position down the field where the receivers hands are? I would think not nearly as likely as a properly stabilized football, or bullet in this case. I truly must divert to an expert in the matter, Shawn Agne. He addresses bullet weight vs. twist in depth in this thread the OP might find useful.


Explain Barrel Twist Rate, 1/7 1/8 Etc... What Does It All Mean?

 

[Ohiobellboy]

I put one in layaway yesterday. Just to give me time to make sure it's the right one and not just an impulse buy. It's a slightly used Ruger AR556. We took it apart at the store looking for signs of wear and can't find any. Not really any marks in it anywhere to indicate it was fired a lot. It already has Daniel Defense furniture on it. A vortex optic that sells for about 200 and aluminum front rails that you can mount crap on all 4 sides to. A little over $300 in extras plus a 2nd mag. Shop wants $670 for it plus the governors share which brings it up to $715 out the door. I figured the extras was worth the $70 more in cost than a new one as I'd have spent some money on an optic anyway.

 

[RangerTim]

You won't regret it! Every good American needs a quality handgun, good shotgun, and AR15!

 

[JustinS]

[QUOTE="Ohiobellboy]I put one in layaway yesterday. Just to give me time to make sure it's the right one and not just an impulse buy. It's a slightly used Ruger AR556. We took it apart at the store looking for signs of wear and can't find any. Not really any marks in it anywhere to indicate it was fired a lot. It already has Daniel Defense furniture on it. A vortex optic that sells for about 200 and aluminum front rails that you can mount crap on all 4 sides to. A little over $300 in extras plus a 2nd mag. Shop wants $670 for it plus the governors share which brings it up to $715 out the door. I figured the extras was worth the $70 more in cost than a new one as I'd have spent some money on an optic anyway.

[/QUOTE]
What a deal. Do they have any more?

 

[Ohiobellboy]

[QUOTE="JustinS]What a deal. Do they have any more?

[/QUOTE]
That was the only used AR they had. That was yesterday though. lol

 

[~ZENAS~]

Explain Barrel Twist Rate, 1/7 1/8 Etc... What Does It All Mean?[/URL]

A barrel variance that throws off groups of one weight of bullet doesn't necessarily affect other weights of bullets in the same way. So just because it shot 55gr poorly and heavier bullets just fine does not mean twist rate is the culprit.


Your football analogy is spot on regarding a twist rate that is too slow for a bullet. However it is completely irrelevant for a twist rate that is "too fast" as in the issue you presented about a 1:7 barrel shooting poorly with 55gr bullets. To continue the football analogy, the tighter your spiral, the better the flight of the football. Now consider those JUGS machines that fire footballs at rates so much faster than any human can throw. Under that tremendous speed and twist rate, that football still spirals true and flies straight as an arrow.


Lastly, we need to keep in mind the issue regarding bullet stabilization and twist rate is one of bullet length, not bullet weight. It's a common mistake to make given that generally speaking longer bullets tend to be heavier, but it isn't always the case. And the real issue is with bullet length, not weight. To understand this, look at the reason the military switched to 1:7 barrels. It was because of the 62gr tracer rounds. They were too long for the slower twist barrels, but the same weight as the m855 ammo that functions just fine in the slower twist guns (even the old 1:12 standard barrels). So in m855 and m856, we see too bullets of the same weight, but very different lengths that have very different twist rate requirements.


My whole point here is that it is a misconception that you can "over-stabilize" a bullet. You can certainly under-stabilize one, but a faster twist rate will not open up your groups. The only risk is it will spin the bullets apart, but I think you'd notice that immediately.


Understanding Twist: Bullet Stabilization


"Over-stabilization" won't result in reduced accuracy (meaning inconsistent groups). The only potential issue you might see downrange is that some ballistics experts theorize that at long ranges (i.e. 500+ yards), the gyroscopic effect of a bullet spinning very fast may result in the tip of the bullet to stay elevated after the arc of the trajectory (the tip pointing upwards even though the bullet is on its way down). Since the bullet is stable because of the spin, it will still fly true and accuracy will be consistent, but the angle of the bullet in flight can cause more surface area for air resistance and mean more drag and lower ballistic coefficient. This means more drop at distance and therefore a change in point of impact. But a change in point of impact isn't the same as bigger groups or decreased accuracy. This is why I still contend there is no such thing as over-stabilization for a bullet.

 

[Ohiobellboy]

And here it is. Another black AR. lol


Side note, while at the fiasco in Avon today aka the Grand Opening of the new Cabelas, I was pricing all kinds of ammo. Won't bother with them again. I was at the local Wally world this evening and picked up 4 boxes of Perfecta 223, 55 grain, 50 rounds per box for $15 per box. We'll see how well that fires as soon as I can get to a range.

 

[~ZENAS~]

Nice rifle. Hope you enjoy it.

 

[Ohiobellboy]

[QUOTE="T.L.Jones]Nice rifle. Hope you enjoy it.

[/QUOTE]
Put 100 rounds through it today. Cheap ammo and the gun both worked flawlessly but boy do I suck with a rifle. lol. Gonna be a learning curve with it and I know I'll be changing out that front grip. I'm still a little weak from my neck surgery a little over 3 weeks ago but I would have thought I'd be able to hold it up better than that.

 

[~ZENAS~]

Hang in there man. I had back surgery in 2011. I was able to start shooting again fairly quickly (a couple months) but I wasn't the same for a couple years. I think I developed some bad habits during recovery that took quite a while to train out of myself. Stick with it and you'll be a pro in no time.

 

[Ohiobellboy]

[QUOTE="T.L.Jones]Hang in there man. I had back surgery in 2011. I was able to start shooting again fairly quickly (a couple months) but I wasn't the same for a couple years. I think I developed some bad habits during recovery that took quite a while to train out of myself. Stick with it and you'll be a pro in no time.

[/QUOTE]
Thanks TL. I need to get with some of my friends that shoot on a regular basis to develop good habits before I learn any bad ones that will be a PITA to get corrected.