Long Range Semi-Auto vs. Bolt Action Rifles

Discussion in 'Rifle Country' started by EdLaver, May 30, 2007.

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  1. tommytrauma

    tommytrauma Member

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    How do they compare in price to a Savage model 10?

    I'm afraid I like too many guns. When I wanted a precision stick, I had to do it on a budget. I found I could pick up a Savage model 10 and some good glass to top it with for less then a SA M1A alone, and the Savage has been sub-MOA with very little tinkering.
     
  2. Groovski

    Groovski Member

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    This hobby can be maddening at times. Just when you think you have a grasp on the basics, you find out you don't know jack. So, I have some questions:

    Ballistic coefficient is related to the shape of a bullet, as I understand it. Why can't a .308 bullet have a ballistic coefficient on par with those of superior cartridges? Would it just be too heavy? Too long? What is it about a .308 that makes it unable to match ballistically superior cartridges? Is the .308 cartridge too small relative to the bullet to give it superior ballistics?

    Consistency seems more nebulous. It would seem consistency would be related solely to a consistent muzzle velocity, and nothing else, because once the bullet leaves the barrel, ballistics take over. What would make one cartridge any more consistent than another, other than a consistent shape, friction on the bullet, amount of powder charge, etc. (things that don't seem related to the cartridge type - .308 etc)?
     
  3. Zak Smith

    Zak Smith Moderator Emeritus

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    To get a .30 caliber bullet with a BC of above 0.60, you need to start at 210gr, which the .308 will not be able to shoot very fast. If you just next 308 down to 6.5mm to get .260 Remington, now you can shoot the 139-142gr bullets (BC around 0.61-0.62) at 2800fps. 308 doesn't have enough powder capacity to bore diameter to shoot high-BC bullets reasonably fast.

    Consistency can be thought of as mechanical accuracy and muzzle velocity. I am not an expert at what differentiates short-range Bench-rest competition rifles for accuracy, where winning groups are in the 0.1 MOA range. However, if you can be satisfied with a rifle that shoots 0.25 MOA groups, it is my belief that you can make a rifle in most calibers that could do it provided good components were available (brass, bullets).

    -z
     
  4. Groovski

    Groovski Member

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    Thanks for the explanation, Zak. So for any caliber, a sort of optimal cartridge design could be devised such that the bullet had a BC of 0.6 or higher, and a muzzle velocity of up to around 3000 fps. There are certainly tradeoffs in doing that, though.

    Back to the theme of the thread, it would seem the .308 was selected by the military more as a semi-auto cartridge than anything else. Perhaps the .308 made a better semi-auto round than bolt-action precision sniper round, because it represented a good compromise between heft of gun/action necessary to fire it, and ballistics (both external and terminal).

    Re: consistency. As I understand it, there are .308 rifles that achieve 0.25, which is on par with other field use rifles. If you get the windage and distance exactly right (a big if), ballistics shouldn't matter, at least until you reach the transonic boundary. Granted, it's difficult to get them right, but given say a stationary man-sized target at 600 yards, a moderately accurate rifle of say 2 MOA, and some moderately skilled windage and distance estimation, you should hit the target all day long with a .308 if you do your part. At 1000 yards, it's much more difficult, but say 30% better ballistics alone isn't going to make up the difference between a hit or miss for significant errors in distance, wind or an innaccurate rifle. Assuming you can get everything right at 1000 yds, things like remaining energy of the round and weight of rifle to accomplish it are important.

    I'm just trying to get a grasp on how much the inferior ballistics of the .308 really matter in practical situations.
     
  5. Zak Smith

    Zak Smith Moderator Emeritus

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    To turn it around, if 260REM has 35% less wind @ 1000 yards than M118LR (.308), then you have 35% more margin of error for wind estimation.

    On your "man-sized all day @ 600 yards", a 2 MOA rifle should be able to put them into a foot, which gives you only 3" (1/2 MOA) of margin on either side.

    Long-range shooters go away from 308 in droves, and hardly anyone is left using it unless their specific "game" has rules which require .308.



    -z
     
  6. Groovski

    Groovski Member

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    Only in cases where you're on the edge of missing. For a man-sized target at 100 yards, it's likely irrelevant because you're typically nowhere near the edge of missing. I'd say that probably holds for most relatively accurate rifles/shooters up to say 500 yards or so, all other things equal. At 1000 yards, with a 10 mph crosswind, drift for a .308 from your website is 92 inches. So hitting an 18-inch wide target requires estimating the wind to within roughly 0.5 mph for a 1 MOA rifle, assuming you shoot perfectly and I did the math right. With a 35% better cartridge, you have to estimate within 0.7 mph. Every bit helps, but the better ballistics alone aren't going to make me into a dead-eye at that range/windspeed. I'd have to be a good shooter/estimator already (and just on the edge of hitting) to really take advantage of it.

    True. Everything else has to be near perfect, which is easier said than done.

    If the cartridge has better ballistics and all the punch, barrel life, rifle weight, economics, availability, range and other factors you need, I guess there's no reason not to adopt it instead of the .308. Why stop at the .260REM, though, if ballistics at long range is important? Why not go with say the .416 Barrett (3250 fps with a .943 ballistic coefficient)? I'm pretty sure it blows away the .260REM as far as ballistics, without looking up the numbers.
     
  7. USSR

    USSR Member

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    Groovski,

    It's one of those things that you can do the math and theoreticals on and decide it's not such a big deal, but when you are actually shooting at 1k, the advantage becomes all too apparent. BTDT.

    Don
     
  8. Red Mist Effect

    Red Mist Effect Member

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    Quote
    My next big purchase is coming up and I am trying to decide if I want a semi-auto .308 or a bolt action for targets at 600 yards. What I like about the semi auto is multiple target aquisition without delay to cycle. What I like about the bolt is accuracy. I would love to hear opinions, pros, and cons.

    Edlaver
    imo the bolt gun has a stronger action can reload a lot finer than a semi neck size only get the primers flat as a tack dont get that in a semi as for multiple target aquisition get a good rem 700 with a couple of five\ten shot mags and you won't no the diff semi's are a pain to clean. find out what the big F class shooters are using and do what they do there been there and tried that.
     
  9. Zak Smith

    Zak Smith Moderator Emeritus

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    The 35%, or whatever it is for the calibers we're comparing, can't make a bad shot into a good rifleman, but it means that you can absorb more wind error and still make hits. It extends the distance to which you can hold merely "edge of plate" in the same conditions. In a full value wind at 1000 yards, you're going to have to dial in either case, but the better caliber will require less clicks and can put up with more mis-estimation. Shooting 308 at 1000 yards, even with the good 155 Scenar loads, requires a lot more diligence than the better calibers for keeping up with wind changes.

    Specifically: cost, size, weight, recoil.
     
  10. Groovski

    Groovski Member

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    I'm not saying it's not a big deal, especially if you're shooting exclusively at 600 or beyond. I haven't taken into account shooter holding errors, which is hard to quantify, but makes everything else all the more important. I have an appreciation for how hard it is with a .308, but I haven't ever shot a 260REM. If the weather cooperates, I'll be shooting my lowly .308 and 7.62x54 on some old propane tanks tomorrow at 600 yds or as far as I can see them through a 4x scope, and will keep in mind this thread.
     
  11. Whitman31

    Whitman31 Member

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    Someone correct me if I'm wrong, but isn't it a total myth that a semi-auto can't be as accurate as a bolt gun. I agree that they are equal, based on the fact that the bullet is clear of the muzzle before any parts begin to move.
     
  12. Davo

    Davo Member

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    Whitman to get the accuracy of a good boltie you are going to spend much more. Even then, the most accurate guns out there are not semi auto.
    This is very apparent in target guns.
    And to the Aussie....get the bolt, it will last forever and not fail!
     
  13. Blackfork

    Blackfork Member

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    Bolt Vs Semi: Lock Time

    One of the factors not mentioned in the discussion so far is lock time. Almost any bolt action, (since it doesn't have a hammer dropping to hit a firing pin), has a much shorter lock time than any AR platform. Longer lock times magnifies shooter error and bad technique.

    Bolt triggers generally are holding the only firing pin back. AR triggers are holding a hammer which has to fall and hit a firing pin. It's only milleseconds, but it doesn't take much to get out of the ten ring standing at 200 yards in a highpower match.
     
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