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Rifle accuracy question.

Discussion in 'Rifle Country' started by waldonbuddy, Feb 18, 2011.

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  1. waldonbuddy

    waldonbuddy member

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    I've often read where the accuracy of the AR15/10's rival bolt action rifles.

    The way I understand it is that the DI system of the Stoner AR design forces the bolt back in a more centered position vs a piston rifle vs a bolt action where nothing moves at all until the operator re-chambers a round manually.

    Where I'm getting confused is that I thought no parts of any rifle are moving at all until the bullet is out of the end of the barrel by a few inches.

    Now if this is true then why would it matter what method of firing the rifle you used for accuracy purpose's. Looks like it would all be up to the barrel for the accuracy part.

    Please explain this to me.........thanks, Mike.
     
  2. MrCleanOK

    MrCleanOK Member

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    They may not move much, but the parts on a semi rifle do start moving before the pill leaves the barrel. If the bullet left the muzzle before the combustion gas could act on the moving parts, it wouldn't have enough back pressure to do the job.
     
  3. chrome_austex

    chrome_austex Member

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    I believe that the moving piston (in a piston system AR or M14, for example) is the reason piston systems are slightly less accurate. But, I forget if its more moving mass or sooner or what.
     
  4. d2wing

    d2wing Member

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    Perhaps it's because the mechanical part, the bolt, moves along the same axis as the centerline of the barrel. There is no rotational torgue like there would be with a piston or operating rod rifle. There could be other reasons but that is a main one. It amazes me
    how many guys think they are smarter than Stoner.
     
  5. Welding Rod

    Welding Rod Member

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    The moving parts in an AR are in the reciever, not on the barrel, and the moving parts are directly inline with the bore, not off to the side.

    Plus the relatively massive solid reciever is not subject to bedding problems like a small action bolted in to a separate stock.

    What exactly the reason for the AR's excellent accuracy is though, I don't know.
     
    Last edited: Feb 18, 2011
  6. waldonbuddy

    waldonbuddy member

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    Well, if the bullet is in fact still in the barrel when things start to move then that explains it for me.
     
  7. MtnCreek

    MtnCreek Member

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    I'm sure the bolt moves before the projectile leaves the barrel, but I have no idea why. My measurements will be off, but it should be close enough. Gass diven AR, 16" barrel: Projectile moves down the barrel, being pushed by gas; let's say it gets up to 3000 fps. Let's say it travels 10" before reaching the gas port. The projectile continues on at 3000 fps and exits the barrel 6" beyond the gas port. At the same time, gas is traveling down the gas tube to operate the bolt/carrier; gas has to move 10" to reach the key.

    Sounds like the projectile will be out of the barrel when the gas is still 4" from the key. One thing I'm not sure about is possible further compression when the gas goes from a
    .223 to a smaller gas tube.

    Somebody please explain. Thanks.
     
  8. jad0110

    jad0110 Member

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    Yep, just like a water hose, squeezing your thumb down over the end increases the water's velocity the same way compressing the expanding gasses increases their velocity such that the BCG is already kicking rearward before bullet exits the barrel (at which point the gas pressure drops to normal atmospheric pressure).

    And actually, the rearward movement of the BCG begins at approimately the moment the bullet begins leaving the case. Because for every action there is an equal and opposite reaction, the case itself travels backwards with enough force that it in all likelihood moves the BCG just a bit on its own.

    Sorry, I'm not a physist, that's the best I can do.
     
  9. 35 Whelen

    35 Whelen Member

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    To answer this question, you need only look at the equipment of shooters who ultimate quest is for accuracy. That'd be benchrest competitors and most snipers. They all use bolt rifles for a reason. Rifles such as the AR by design must be disassembled to be maintained. This in and of itself will detract from the accuracy potential of the rifle.

    An AR type rifle might rival the accuracy of some bolt rifles, but not a high quality bolt rifle.
    35W
     
  10. mc223

    mc223 Member

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    The analogies of why ARs are or are not accurate as a bolt guns go on forever and usually end up in a stalemate of sorts. With proponents and opponents sinking back to their chosen corners.
    Bolt gunners believe in the stiffness of the action and positive locking. With proper bolt face alignment and ammunition that is made specifically for the chamber and some sort of precision custom lapped barrel. All components are kept as rigid as possible.

    ARs are basically the same with regard to stiffness of the action to a point. There is also a looseness to the action. I think that looseness or the ability of the action to float and to come into alignment as a result of the forces that are applied is at least partially responsible for accuracy.
     
  11. oerllikon

    oerllikon Member

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    I think the gas system may have something to do with barrel harmonics as well. I think that was a part of the early ruger mini 14s pie tin accuracy. I could be wrong though, wouldnt be the first time
     
  12. Rancho Relaxo

    Rancho Relaxo Member

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    What he said!
     
  13. Skyshot

    Skyshot Member

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    I don't see many AR's at benchrest comps.
     
  14. PapaG

    PapaG Member

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    I don't know about moving parts and stuff, although in any mechanical system there is tolerance and clearance so there is some movement, however minute. I do know about the rifles I've shot over the last fifty or more years and I'm now shooting the easiest out-of-the-box grouping gun I've ever had. I had a Number 1 in 222 way back in the early seventies....easy to get an inch. Had a 700BDL in 222, worked but could get an inch. Had a Savage 22-250 benchrest gun (factory) and worked my butt off to get an inch...which rarely happened. Have a pre-64 '70 in '06 which, with work and patience gets me an inch and a quarter with cast bulllets. Pair of 77 MKIIs, one in 243, other in 308, still looking for that moa. An old 788 in 308 was a cinch for an inch with Federal loads. Lots of other guns wouldn't go into two inches. Black powder Rollng block on a smokeless action, 45-70, would do an inch or so all day with duplex (5 gr dupont bulk shotgun, 55 gr FFg, breech seated bullet) and under 4 at 200 (aperture sights).
    Now for the fun gun. Resisted black guns all my life. Finally gave in. Bushmaster, just like the old M16 but semi. First trip to the range. High mounted scope on carry handle, handloads with starting load of Varget, 55 grain Sierra soft point, full length sized, sorted by brand, trimmed. Third group of the day, inch and a half, next inch, final five-eighths after getting used to the trigger and scope...all 100 yards. First load, first trip, too much fun. I can remember working with a gun and load for months to get under an inch. Nothing tuned here. Luck? Must be some as I'm now in the bifocal class with sixty-six year old eyes and a bad back. Sure is fun, though.
     
  15. PapaG

    PapaG Member

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    Forgot to put in the last thought....age, you know. I am sure that each and every rifle is a law unto itself..some like everything, some you have to work with. I believe bedding, a good barrel and a balanced load trump anything else but luck. My brother had luck. He could pick up a gun at a gun show, load some ammo with just about anything from the book and go out and turn in some impressive groups.
    For some reason, and from watching buddies with theirs and from my recent experiences, I am now a believer in the AR platform as an inherently accurate rifle, moving parts or not.
     
  16. d2wing

    d2wing Member

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    As soon as the bullet leaves the cartridge the entire rifle moves slightly as the bolt is still locked, Then the bolt carrier moves first and turns the bolt unlocking it. I don't know the timing but I'm guessing the bullet is gone when the bolt unlocks and actually moves with the BCG. For benchrest a bolt is the ultimate, but in a sport rifle it's much closer.
     
  17. jmr40

    jmr40 Member

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    Bolt rifles are generally more accurate for several reasons. The bolt locks up tighter, better triggers and barrels that are easily free floated. It is a simple design that is easy to get every thing right.

    That said, I've got 2 AR's that are more accurate than any hunting rifle I own. A dedicated target rifle may beat them by a touch, but it would take someone better than me behind the trigger to make it happen. I don't really know why, but the AR's I've owned and shot were very accurate.
     
  18. suzukisam

    suzukisam Member

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    I've got two ARs that I would put up against about any bolt gun out there. I have a rem 700, wby mkV stainless, savage, Mauser, wby vangaurd, another savage. and my 243 will put any one of them to shame. you could cover a 6-8 shot group with a quarter at 200. 1.5" at 300. and ARs are starting to be used in benchrest. I was actually looking at a funny AR at a buddies custom shop tonight and he was explaning to me that he is building them now because they are more popular than they used to be. for some reason it really urks the dedicated bolt guys that ARs can be so accurate. I personally like all classes of firearms so I'm glad that you can get a battle rifle, bench rifle, or bolt that shoots that good. I have actually had more accuracy issues with bolts than autos. I've also owned way more bolts too. And my ARs are all custom built for the most part. oh and the barret mag fed 50 (sniper) is not a bolt.
     
  19. Welding Rod

    Welding Rod Member

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    While certainly not competitive bench guns, my "low grade" stock production RRA ARs are all easily in the sub 3/4 to sub-MOA range with factory loaded match ammo.

    Not too shabby, I think.

    Not sure how "low grade" untouched bolt guns stack up to that. Is a Ruger Hawkeye, Rem 700, or Win 70 normally much more accurate that that?
     
  20. d2wing

    d2wing Member

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    In addition to linear mechanical action, I think the gas action absorbs much of the recoil reducing muzzle movement.
     
  21. Dr T

    Dr T Member

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    The accuracy may be tied to something other than the mechanics of the action: It may be more due to the quality of the CAD/CAM (Computer aided design/computer aided manufacturing) equipment used to manufacture the ARs (and new bolt designs like the T/C Icon and Venture).

    I love finely made, hand crafted rifles. But few workmen can rival the consistency or precision of one of the current generation computer-driven machines (while my Remington R-15 does not have as much Soul as my No. 1 RSI, it is still a darn sight more accurate). While many of the hand crafted rifles achieve accuracy due to hard work and painstaking craftsmanship, many producers achieve it as a matter of course through automated manufacturing and quality control methods based on military standards (which can be rather unforgiving at times).

    This same thing applies to other mechanical items for which we used to rely on skill to achieve perfection. Consider the razor. When was the last time you got a shave or trim from a cut throat razor? I would wager that for most of us it has been a number of years (and some guys may actually be wondering what a cut throat razor is). One reason is that it is very difficult to achieve the sharp edge that can be mass produced using special steels and exotic manufacturing processes used by Gillette and other manufacturers that produce millions of the blades every year.
     
  22. Sunray

    Sunray Member

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    "...the bullet is gone when the bolt unlocks and actually moves..." Yep. Pressures have to drop before the action starts opening or all kinds of bad things will happen. On most semi's the action does nothing until the gases make it happen. The gases don't get into the gas system until the bullet is past the gas hole.
     
  23. steven58

    steven58 Member

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    Here's how I have heard it explained:

    A chief ingredient in the recipe for firearms accuracy is repeatability. Yes, you need a good barrel, stiff receiver, fast lock time crisp trigger and a precise sighting system as well. However, when you fire, everything in that rifle that has mass (ie everything) is going to move as a wave of energy passes through the rifle.

    The trick is to get all that motion to be minimal and to have all of the parts of the rifle come back to exactly the same place every time.

    In a bolt action it's relatively simple: you full bed / free float the barrel in a way that the "wave" moves through the rifle clean with everything returning to the same place. You tune your load / adjust your muzzle weight so the bullet leaves the barrel at the same point in the wave every time.

    In a Semi auto, it's a bit more complex. you have reciprocating parts, usually moving on different vectors than the bullet and in an unsynchronized way. That tends to flap all of the rifle parts around so that they don't come back to exactly the same place each time.

    What the AR does is first, reduce the number of reciprocating parts. Second, lighten each one as much as is practical. Third, move these little parts in a straight line in a synchronized way.

    By using a gas tube instead of an operating rod and piston along the barrel, you eliminate a large mass that normally slams back and forth torquing the barrel and action all over the place each cycle. next make the bolt, and bolt carrier lighter than is normally possible.

    Next Take a stiff milled forging of a receiver, screw the barrel in to it, draw a straight line through this and place all of the reciprocating parts on that line. The barrel lines up with the bolt which is ultra light, and is also the piston (yes an AR has a piston it's just been moved so it's in a straight line with all of the other reciprocating parts) that goes into a concentric bolt carrier. The bolt carrier is ultra light so right behind it is a buffer weight backed up by the action spring. All in a straight line. Some genius.

    Now comes the REAL genius. Ordinarily, the bolt would be to light to function without tearing itself up rather quickly from the unlocking forces on those little bolt lugs. But, in the first few microseconds of fire, the gas moves down the tube into the bolt carrier filling the piston chamber evenly and as the bolt carrier begins to move back, the bolt moves FORWARD a small amount unloading the forces on it before it rotates and unlocks and the entire bolt and carrier begin to move back. As the bolt carrier is light the initial motion is less energetic and violent than if you combined the mass of recoil buffer and the bolt carrier as in a traditional semi auto. this stretches out the cycle smoothing it and reducing the effect of the reciprocating parts.

    Also, since all reciprocation is concentric to the bore, you no longer need rails milled into or spot welded to the receiver to force everything to move in a straight line.

    Here is a long stroke gas piston rifle flapping around http://www.youtube.com/watch?v=xeeeFxA_9nA&feature=related

    Here are the M1-A and M1 Garand http://www.youtube.com/watch?v=SgldaFmgPZo Watch the barrel motion.

    Here's an M16 head to head with an AK http://www.youtube.com/watch?v=G6BpI3xD6h0
     
    Last edited: Feb 19, 2011
  24. Art Eatman

    Art Eatman Administrator Staff Member

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    I played pawnshop for a guy on a Bushmaster Match Target. Probably around ten years back, +/-. Mediocre trigger, but it was half-MOA anytime I shot it. For all I could tell, with slow fire it wouldn't really matter how many shots in a string, it would have been half-MOA all day long, barring shooter fatigue. Best semi-auto I've ever shot.

    I've had a lot of half-MOA bolt actions, but I've never tested them that much for sustained tight groups.
     
  25. mljdeckard

    mljdeckard Member

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    For ARs, I have found the limiting factor is the barrel. If you spring for a Krieger barrel, and have it installed properly, it will be as accurate as any bolt rifle I have ever shot. The AR design is inherently accurate for ANY kind of rifle, despite the perceived mechanical disadvantages. The average lock time on an average bolt rifle is about 4 milliseconds. For ARs it's more like 16 milliseconds. For a rifle you can build yourself as an amateur, an AR can't be beat.
     
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