Thought to Ponder with a Few Idle Minutes

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TEX
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Thought to Ponder with a Few Idle Minutes

Postby TEX » Sun Jan 14, 2018 2:35 pm

Be warned that this post is for those who like to muse odd things and have a few extra minutes to while away.

I had read sometime back that one small reason an AR would not or could not be as accurate as a good bolt action gun is that essentially the AR is hammer fired whereas most bolt guns are basically striker fired - and that the extra time delay and impact of the hammer against the firing pin affects accuracy in a negative manner. Very anal point I would agree as I have seen plenty of very accurate ARs and 1911s - of which 1911s are hammer fired and generally known to be somewhat more accurate than striker fired pistols, although I personally write that off as being due to a shorter and generally crisper trigger release and the barrel bushing.

So my question or request for opinions is; would it really make a difference in a pistol, and if so, at what difference would it make a difference. I certainly think it would be hard to measure any difference short of 7-8 yards.

Any thoughts are welcome even sarcastic ones : )
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Re: Thought to Ponder with a Few Idle Minutes

Postby oohrah » Sun Jan 14, 2018 10:29 pm

My understanding of accuracy in a gas operated semi automatic rifle is that the gas sidelined for the SA operation is taken away from the gas used to propel the bullet and that amount is not always the same/controllable. Whereas in a bolt action, all of the gas is used to propel the bullet, and the loader can control the amount of charge very accurately, which is why sniper rifles are always bolt action.

I recall the M1 and the AR-15 both use essentially the same type of gas operation. However, the M14 design recognized this problem, and tried to alleviate it somewhat by providing a gas capture cylinder that would supposedly trap the same amount of operating gas each time. I do not know how effective that was compared to the M1, but I never heard of snipers/competition shooters adopting the M14.
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Re: Thought to Ponder with a Few Idle Minutes

Postby Medley86 » Sun Jan 14, 2018 11:38 pm

My ar15 with a decent factory load shoots far better groups than my r700 .270 bolt action using the rounds I deer hunt with. Both guns are probably more accurate than I am really capable of using.
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Re: Thought to Ponder with a Few Idle Minutes

Postby jmorris » Tue Jan 16, 2018 10:45 am

oohrah wrote:........ I do not know how effective that was compared to the M1, but I never heard of snipers/competition shooters adopting the M14.


Marine designated marksman. Fills a niche between rifleman and sniper. The M14 is upgraded. Army uses a modified M16 IIRC.

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Re: Thought to Ponder with a Few Idle Minutes

Postby Bitter Clinger » Tue Jan 16, 2018 10:54 am

TEX wrote:Be warned that this post is for those who like to muse odd things and have a few extra minutes to while away.

I had read sometime back that one small reason an AR would not or could not be as accurate as a good bolt action gun is that essentially the AR is hammer fired whereas most bolt guns are basically striker fired - and that the extra time delay and impact of the hammer against the firing pin affects accuracy in a negative manner. )


In theory yes, in practice not so much. As had been presented on this forum in prior threads, after a certain distance, the ability to make good wind calls is more important than anything else.
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Re: Thought to Ponder with a Few Idle Minutes

Postby cmgee67 » Tue Jan 16, 2018 12:11 pm

So how exactly does a barrel determine the accuracy of the bullet. If someone says the barrel is innacurate how does that cause the bullet to vear off track? Is it the rifling? Gas? Imperfection in the bullet? Shooter? I’m sure all of that comes into play but I’m just curious.
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Re: Thought to Ponder with a Few Idle Minutes

Postby LeonCarr » Tue Jan 16, 2018 5:58 pm

IME it takes a well tuned bolt action rifle to out shoot an AR.

In 1991 I bought my first AR, a Colt Blue Label R6601 Match HBAR. With Black Hills 52 Grain BTHP Ammunition it would shoot 1 inch or better 3 shot groups with open sights off the bench at 100 yards. IME it takes a match conditioned bolt action rifle with match type peep sights to shoot as good as that bone stock Colt AR, and it will cost more money.

About a year later, a buddy shows up at the range with an Olympic Arms Ultramatch Rifle. 20 inch Ultramatch broach cut stainless steel barrel, the old school knurled aluminum free float handguard, Krieger/Milazzo type set trigger, 6.5-20 Leupold Vari X-III scope, shooting the same Black Hills 52 Grain BTHP. Five shots into 1/4 inch off the bench at 100 yards. Bad groups according to him were .3s and .4s. To this day it is the most accurate AR I have ever shot. Except for the set trigger, that was a mass produced, off the shelf Olympic Arms Rifle with no special tuning. At the time my buddy had about 1100 bucks in that rifle. IME it takes a well tuned varmint type bolt action rifle or benchrest rifle to shoot like that off the shelf varmint type AR, and it will cost more money.

IME good barrels and good bullets are what make ARs shoot, along with a design that requires no bedding or special stock treatment. Yes the AR trigger has a slower lock time, but focusing on your follow through along with sound shooting fundamentals will take care of that.

Just my .02,
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Re: Thought to Ponder with a Few Idle Minutes

Postby The Annoyed Man » Tue Jan 16, 2018 11:50 pm

cmgee67 wrote:So how exactly does a barrel determine the accuracy of the bullet. If someone says the barrel is innacurate how does that cause the bullet to vear off track? Is it the rifling? Gas? Imperfection in the bullet? Shooter? I’m sure all of that comes into play but I’m just curious.

The barrel isn’t the only thing that affects accuracy, but the barrel can affect accuracy primarily in three ways: barrel weight, barrel length, and barrel twist.

BARREL WEIGHT: Given two barrels of equal length, the heavier barrel will be stiffer. A stiffer barrel dampens barrel harmonics - the frequency and amplitude of barrel vibration as the shot is fired. The greater the amplitude of the vibrations at the muzzle, the greater the “spread” will be at the point of impact. The heavier barrel vibrates with less amplitude and frequency at the barrel, thus the spread at POI is smaller, which equals better accuracy.

BARREL LENGTH: Up to some “ideal” length, the longer the barrel, the greater the muzzle velocity as the powder is able to achieve a complete burn while in the bore. The greater the velocity, the higher the bullet’s ballistic coefficient (BC). The higher the bullet’s BC, the more stable it will be in flight, and the longer it will remain stable over the length of its trajectory. Stable bullets are more likely to behave the same, one shot to the next, which increases consistency of performance at the POI. At some point, the barrel is TOO long, which is when the powder has finished burning inside the bore and the gasses are no longer expanding at sufficient rate to continue accelerating the bullet. Every inch of bore from end of combustion to muzzle creates friction which begins to slow the bullet down....which decreases its BC, etc., etc. The ideal length of barrel for cartridges like .308, .30-06, .270, etc., in a bolt action rifle, appears to be between 22” to 26”. That’s why you see most hunting rifles in those common hunting calibers with barrels in that range of lengths. HOWEVER: that kind of barrel length is not optimum in a battle rifle, which is why modern battle rifles like ARs, SR25/M110s, SCAR 16s and 17s, etc, tend to have barrel lengths of 20” or less.....mostly around 16”-18”. In that case, greater range (and for the most part, greater accuracy) is being given up in exchange for portability, CQB requirements, weight, etc.

BARREL TWIST: Generally speaking, there is a range of twist rates - measured as the length of bore required for the rifling to complete 1 full turn - which is ideal for any given caliber. For instance, in .223/5.56, twists of 1:12”, 1:9”, 1:8”, and 1:7” are used, with the latter 3 being the most common. A “tighter” twist completes one full turn in a shorter length of bore. So a 1:7 twist is “tighter” than a 1:9 twist. As a general rule for any given caliber, the tighter the twist, the better it will be at stabilizing heavy-for-caliber bullets, and the longer the twist, the better it will stabilize light-for-caliber bullets. If a light bullet is fired at a high velocity through a too-tight twist, that bullet can be spun fast enough to cause it to come apart in flight, or to cause it to spin itself off of the desired trajectory.....in other words, your fastball becomes a curve. So if you shoot 45 grain .224 bullets through a 1:7 twist with a MV of 3300 fps, you’ll likely lose accuracy. But if you shoot a 75 grain bullet through that same barrel, you’ll see a marked improvement in accuracy.

Pick a barrel of optimum weight (the heaviest you can realistically tote around in the field), optimum length (the longest you can realistically tote in the field that allows optimum powder burn without slowing the bullet down), and the optimum twist for the ammo you will be shooting, and that will give you the best accuracy you can expect for a hunting rifle. For example, a .308 bolt action, shooting bullets in the 150 to 165 grain range, through a 22” barrel with a 1:12 twist will be fine. That will give you the velocities you’d like to see for optimum terminal ballistics.

For a target rifle you’ll be shooting either from a bench, or from the prone on a rest like a bipod, a heavy, longer barrel of tighter twist will let you shoot heavier bullets at higher velocities over longer ranges. For instance, a .308 bolt action, shooting bullets in the 168 to 208 grain range, through a 24” to 26” barrel with a 1:10 twist will be fine. That would give you enough to heavy bullets further while retaining enough velocity to keep their BC up over longer ranges.

Mind you these are all generalities, and each rifle is an individual weapon with its own characteristics. Here’s another “general” rule: Bolt actions tend as a class to be more accurate than semiautos. The reason is mostly because the bolt gun will achieve consistent lockup from shot to shot, but the superior rigidity of action in a bolt gun comes into play, as well as the likelihood that your mass-produced milspec barrel for an AR is just not made to the same tolerances as the barrel in say a good Remington 700 or Savage 10. That does not mean that you can’t build a semiauto that will outshoot a bolt gun. My son used to have a AR15 varmint rifle that would put 4 77 grain OTM into .25” at 100 yards. That’s crazy good accuracy, and better than any of our bolt actions, which are very accurate rifles in their own right. But as a general thing, I would take a bolt action over a semiauto of the same caliber most of the time, if accuracy were my primary objective. But even among semiautos as a class, the above factors of barrel weight, barrel length, and barrel twist still apply, just as they do in a bolt gun.

And exactly NONE of this has anything to do with the accuracy of the bullet itself, which is a separate issue. For instance, in .308, while will a 168 grain Sierra Matchking perform better than a 165 grain Federal Fusion bullet? (Hint: look for the word “match”.....) A crappy barrel won’t make a match bullet fly accurately, and a great barrel can’t make a crappy bullet fly accurately. But a good barrel with a good bullet is gold, and a great barrel with a great bullet is magic.

I hope that helps.
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