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Thread: Grain question - .243 v .308

  1. #1

    Grain question - .243 v .308

    Hi all,

    I've got my FAC application in at the moment and have asked for a .308 as its a caliber I know like the back of my hand, having shot comfortably in excess of 10,000 rounds of it over the years at Bisley (target rifle) at all sorts of ranges from 300yds - 1000yds.

    I've put down for "deer, AOLQ and for zeroing/practice" so my question is this;

    In the event that I was using this for foxes with, say, a 90 grain load what would be the difference between a .308 90 grain cartridge and a .243 90 grain cartridge in terms of ballistics and energy?

    So far as I can tell they are both 90 grain in weight and are fired from the same case length with the same powder load behind them, its just one of them is a larger diameter than the other? So therefore the muzzle energy and ballistics should be pretty similar, if not identical?

    Maybe I'm missing something here but to me that makes sense.

    Appreciate your thoughts!

  2. #2
    A little more complicated, due to the fact that an identical powder charge would effect the bullet differently in the different chamberings.

    Might be be better to compare the bullets given a different powder charge but an identical muzzle velocity?

  3. #3
    Not sure about a 90 grain, but a .308 will send a 100 grain down the road at 3300 fps and a .243 would send a 100 grain down at 3200 fps. However, if on the foxes you are more likely to have your .243 loaded with 55 grain which would be sent at about 4000 fps.

    Your .308 100 grain also has the aerodynamic of a brick, so your 250 yd Charlie is going to need a bit of adjusting for, especially if it's a windy night. The .243 however would make the shot much easier with no compensation for trajectory and not much for windage.

    You can shoot foxes with a .308, but it wouldn't be my first weapon of choice.
    So much to learn and so little time left

  4. #4
    You can't push a 100-gr bullet as fast from a .243 bore as fast as you can from a .308 bore, without a lot higher pressure, because the .308 has so much more area on which the gas pressure can work.

    If you are shooting foxes with a .308 Win, I assume the range is not terribly far ( under 200 yards ). So you could load up a 100 or 110-gr varmint cartridge with a bit of aerodynamics, and launch it with a mild charge of H-4895, IMR-3031, H-4198, or Blue Dot powder, at the same velocity as your deer load (say, 150-gr at 2,700 fps), so as to minimize sight fiddling and too much thinking.
    Last edited by Southern; 23-02-2016 at 16:37.

  5. #5
    I'm new to 308, having bought one last summer to compliment my 243, but after messing with 2 rounds in the 243 (100gr for deer and 58gr for foxes) I have decided to stick to just the one round in the 308 (150gr SST), I know where it goes and don't have to mess around adjusting/guessing where it is going.

    Seems to work so far...

  6. #6
    Quote Originally Posted by Southern View Post
    You can't push a 100-gr bullet as fast from a .243 bore as fast as you can from a .308 bore, without a lot higher pressure, because the .308 has so much more area on which the gas pressure can work.

    If you are shooting foxes with a .308 Win, I assume the range is not terribly far ( under 200 yards ). So you could load up a 100 or 110-gr varmint cartridge with a bit of aerodynamics, and launch it with a mild charge of H-4895, IMR-3031, H-4198, or Blue Dot powder, at the same velocity as your deer load (say, 150-gr at 2,700 fps), so as to minimize sight fiddling and too much thinking.
    Quote Originally Posted by karlbird View Post
    I'm new to 308, having bought one last summer to compliment my 243, but after messing with 2 rounds in the 243 (100gr for deer and 58gr for foxes) I have decided to stick to just the one round in the 308 (150gr SST), I know where it goes and don't have to mess around adjusting/guessing where it is going.

    Seems to work so far...
    Thats sorta the direction I was leaning towards - 100gr for foxes and 150gr for deer, job done. And definitely good to know I can run a milder powder in the lighter load to avoid sight tweakage.

    Thanks all for your replies, really interesting to hear everyones thoughts! Much appreciated!

  7. #7
    Use one bullet - You don't want to be swapping bullets when the "wrong" quary presents itself. - either 130 or 150 grain in a 308 does it all for fox & deer at stalking distances in Uk. No tweaking necessary. 130 grain produces lower recoil & 150 grain is better balisically at longer ranges & in wind. Barnes TTSX gets my vote in either weight. Can be a bit difficult to source but well worth it.

    Ian

  8. #8
    why are you messing about with different bullet weights for different things ?just find a bullet that suits your needs 150 -155 grain and use that don't make life complicated .

  9. #9
    SD Regular Greener Jim's Avatar
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    I agree with just using one load. A 150gr will stop a fox.

    What Southern said is correct. I would add that a 100gr .308 is much shorter than a 100gr .243 therefore the former has more useable case capacity. Also, the 308 bore has more volume for the gases to expand in to than the .243 given the same length barrel.

    Basically the 308 would drastically out perform the 243 with a 100gr bullet in each. The 243 will push a 100gr@3000-3100fps (Hodgdon and Alliant data). The 308 will push a 110gr Barnes@3200-3300fps according to Hodgdon (or even high 3500's according to Barnes)!
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  10. #10
    What you will find with the short 100 gn 308 bullet is that its shorty stubby shape (low ballistic coefficient) will quickly loose velocity so that it's ultimate trajectory may not be that flat. Equally it won't have particularly good penetration, but for a Fox thats probably ideal.

    Take the Hornady .308 110 gn V-Max - Hornady Manufacturing Company :: Bullets :: Rifle :: Choose by Caliber :: .308 30 CAL :: 30 Cal .308 110 gr V-MAX® with a ballistic coefficient of .29

    Put it into the Ballistics calculator - Ballistics Calculator - Hornady Manufacturing, Inc - its 3.5" low at 200 and 30.5" low at 400 yds. (assuming 100 yd zero and 3000 MV).

    Whereas .243 105 gn Amax - Hornady Manufacturing Company :: Bullets :: Rifle :: Choose by Caliber :: .243 6mm :: 6mm .243 105 gr A-MAX® with a ballistic coefficient of .500 and MV of 3000 fps will be 2.9" low at 200 yds, at 400 its 24.6" low.

    So in practice not a huge difference and certainly not enough to worry about at 200 yds.

    One thing to consider though is that foxes are a small animal and with a 308 / 7mm etc especially with deer bullets you will get complete penetration, whereas a small 222 or 243 50 gn varmint bullet will have a small entry hole and vaporise internally. You won't want to eat the Fox, but the bullet is not going anywhere else.

    I have had a few foxes run after being hit with a 7mm soft point deer bullet through the chest. They were dead but ran quite a considerable distance with little expansion of the bullet. Nothing wrong with the shot, nothing wrong with the bullet but the 139 gn Hornady soft point will also work on large deer and antelope.

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