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What makes a 308 have a flatter trajectory then a 30-30 when there both 7.62 51 mm shouldn't they be the same round

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  • What makes a 308 have a flatter trajectory then a 30-30 when there both 7.62 51 mm shouldn't they be the same round

    What makes a 308 have a flatter trajectory then a 30-30 when there both 7.62 51 mm shouldn't they be the same round

  • #2
    The BC is going to be lower in a 30-30 then the .308. You have to use round nose bullets in a 30-30, where in a .308 you can get a better BC.
    But yes there both .30 cal. bullets.

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    • #3
      Yes they're both 30 cal. and 51mm long, but they still have different case dimensions, and the 30-30 is rimmed while the 308 Win. isn't. The 30-30 has a skinnier body, a longer neck, less case capacity, and a less steep shoulder. The difference in trajectory is because the 30-30 holds less powder and has less aerodynamic bullets.

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      • #4
        A major reason is the .308 has a much higher velocity and therefore a flatter trajectory.

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        • #5
          Simple. Regardless of bullet configuration, there is more powder and faster burning powder pushing the bullet from the .308. In other words, the .308 has a bigger engine.

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          • #6
            This is really a basic ballistics question. Are you just starting out? I would recommend you read up on how rifle cartridges perform, what determines the velocity of various loads, what are the inputs and variables in bullet drop and trajectories. This will give you a good start in answering your own question.

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            • #7
              Speed is the only difference. If you drop a bullet from your hand, it will fall at 32 feet per second, accelerating another 32 feet per second for each second of flight. That is the force of gravity and it is exactly the same whether you drop a 50g bullet or a 500g bullet.

              Because of the exact same gravitational force on each cartridge, bullets from both rifles drop at exactly that same speed. The only difference in their range or "drop" is that the .308 is going faster, allowing it to be further down range before it hits the ground assuming you are shooting both rifles perfectly level over a flat surface.

              There are two factors that influence speed of a bullet:

              1. Making a bullet go faster - Using larger cartridge cases, more powder, smaller projectiles, hotter primers, changing bullet jump from the case to the rifling, etc. are all methods of increasing a projectile's velocity but the SPEED of the projectile is the only thing that determines its drop at a given range.

              2. Maintaining bullet speed - A projectile's shape and mass affect its ability to maintain its initial speed as it passes through the friction of our atmosphere. Some projectile shapes slow down fast (e.g. flat nosed, flat based) and some shapes maintain their speed (e.g. a boat tail and secant ogive on a Very Low Drag bullet) exceptionally well. With regard to mass, lighter bullets slow down faster than heavy bullets. For example if you throw a ping pong ball it will drop much faster than a rock because of its very low weight. When it comes to bullets, shooting a 20g .17 HMR is a bit like throwing pepper into the wind, while shooting a 250g .338 Lapua VLD bullet is more like shining a laser. Both start out at similar speeds but the .338 goes a LOT further.

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              • #8
                The .30-30 or 7.62x51R (Rimmed) is an older design well-suited to the lever, pump and bolt action rifles for which it is chambered; however, if you stand it beside the 7.62x51 or .308 Winchester cartridge is a rimless bottleneck cartridge with a significantly greater case capacity and internal dimensions that operates at higher chamber pressure, and you can see the difference in case shape in a side-by-side comparison. What you can't see (but will immediately notice when you fire them in their respective rifles/carbines) is the much greater bullet velocity of the .308 Win.
                The .308 is a product of the '50s, a more modern cartridge and smokeless propellent combination. The cartridge case itself is stronger, thicker at the base and operates at a chamber pressure of 60,000 psi. The .30-30 Win operates at 40-42,000 psi. The bullet diameter is the same (0.308"), and the bullet weight options (say 150 gr.) can be the same, but the difference in pressure provides the .308 Winchester with a greater bullet velocity. That increased velocity provides a flatter trajectory over distance. Briefly, same bullet diameter but a significantly larger "combustion chamber" on the .308 Win.

                Comment


                • #9
                  Originally posted by DakotaMan View Post
                  Speed is the only difference. If you drop a bullet from your hand, it will fall at 32 feet per second, accelerating another 32 feet per second for each second of flight. That is the force of gravity and it is exactly the same whether you drop a 50g bullet or a 500g bullet.

                  Because of the exact same gravitational force on each cartridge, bullets from both rifles drop at exactly that same speed. The only difference in their range or "drop" is that the .308 is going faster, allowing it to be further down range before it hits the ground assuming you are shooting both rifles perfectly level over a flat surface.

                  There are two factors that influence speed of a bullet:

                  1. Making a bullet go faster - Using larger cartridge cases, more powder, smaller projectiles, hotter primers, changing bullet jump from the case to the rifling, etc. are all methods of increasing a projectile's velocity but the SPEED of the projectile is the only thing that determines its drop at a given range.

                  2. Maintaining bullet speed - A projectile's shape and mass affect its ability to maintain its initial speed as it passes through the friction of our atmosphere. Some projectile shapes slow down fast (e.g. flat nosed, flat based) and some shapes maintain their speed (e.g. a boat tail and secant ogive on a Very Low Drag bullet) exceptionally well. With regard to mass, lighter bullets slow down faster than heavy bullets. For example if you throw a ping pong ball it will drop much faster than a rock because of its very low weight. When it comes to bullets, shooting a 20g .17 HMR is a bit like throwing pepper into the wind, while shooting a 250g .338 Lapua VLD bullet is more like shining a laser. Both start out at similar speeds but the .338 goes a LOT further.
                  Well said

                  Comment


                  • #10
                    Originally posted by DSMbirddog View Post
                    This is really a basic ballistics question. Are you just starting out? I would recommend you read up on how rifle cartridges perform, what determines the velocity of various loads, what are the inputs and variables in bullet drop and trajectories. This will give you a good start in answering your own question.
                    there is a difference between the 308 and the 7.62 NATO. The NATO case is thicker/heavier and it's a much hotter load

                    Comment


                    • #11
                      There is a difference between the 308 and the 7.62 NATO. The NATO case is thicker/heavier and it's a much hotter load

                      Comment

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