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Thread: Thoughts on reloading 308 in short barrels 18" or less

  1. #1

    Thoughts on reloading 308 in short barrels 18" or less

    I currently reload a 308 round for a pal (48 grains of vit 140 under a 130 grain Hornaday soft point with a cci br2 primer) which he gets along with fairly well for shooting Roe and the occasional Red from a Sako model 85 lightweight hunter with a 20" barrel.
    He is wanting to reduce the barrel to 18" or slightly less. Having taken a little time to develop this currrent load, as we couldnt get it to shoot a 150 grain bullet, I am concerned that shortening the barrel as he wants to might cause the 130 grain to become unstable at range as the velocity drops off.
    If anyone has experince with 308 in these sort of barrel lengths I would appreciate their thoughts, especialy on powder choice.

  2. #2
    Although you are making the barrel a little shorter you are not actually changing the rate at which the bullet is going to be spinning and so you should not have stability problems, especially not with those light for caliber bullets you are loading up. There is some thought that it might take the bullet a little while to "take" the rifling but I think this happens in a very short distance indeed so by 18 inches your bullet will be spinning as fast as if the barrel were 28 inches long.

    Now, you might reduce the velocity a little and that will have a small impact upon the rate at which you spin the bullet in terms of revs per minute but I would imagine this would be very marginal and, again, the fact that the bullet you are shooting will be very easy to stablise due to it being relatively short will work in your favour.

    The other thing that occurs to me is that maybe you are concerned about the velocity dropping below the super sonic but your loss of velocity will not be so great, maybe 50fps per inch or a little more.

  3. #3
    Hi Coaroach,
    Thanks for reply, take on board your comments. My concern was about velocity especially at longer ranges, although not particularly the ranges at which you would take a deer at. My thought process was along the lines that it might be advantageous to use a faster burning powder to get that velocity back, but I was concerned about increased pressure and recoil.

  4. #4
    Sorry Caorach, just noticed my spelling.

  5. #5
    Although shortening the barrel obviously doesn't change the twist rate, the rpm of a bullet will be less if it is travelling slower at the muzzle. eg 1 in 11 twist at 2500fps = 137500rpm at 2700= 148500rpm All academic really, you'll have no worries with the 130's. I used N135 with 155's in my 308 with a 20" barrel it gave less muzzle blast than varget or N140 and no noticable difference in accuracy or recoil and very slightly, better velocity.

  6. #6
    I am firing factory 165s out of my 20 inch .308 and I am getting better than MOA at 100m.

    I recon you should acheive 2800 with your 48 grain of vit over the 130s without too much dificulty

    Last edited by devilishdave; 03-02-2011 at 01:44.

  7. #7
    A bullet in flight is rotating on an "air" bearing. Air bearing are almost frictionless. The amount of change in rotational velocity is almost unmeasurable. Reducing muzzle (linear) velocity - regardless of method - will reduce rotational velocity, BUT... If the bullet is gyroscopically stable at 10 yards it will have all the rotational velocity it needs to be gyroscopically stable at 1000 yds. "Instability" at longer ranges due to LINEAR velocity reduction is a function of transiting the sonic 'barrier', NOT reduction in rotational velocity.


  8. #8
    I have cut nearly every rifle i have owned, my experience (and that of numerous friends) is that once the barrel is cut we have had to reduce the powder charge to achieve the same accuracy as before. The accuracy is not the problem, this is always achievable with a little work re loading. The amount you cut off will obviously affect the amount of powder needed I.E. the more you cut off the less powder is needed.
    As an example in .243 using H4350 four of us cut our barrels to the same length (we had been using the same re load), we all needed to reduce the load by the same amount to achieve the cloverleaf groups we had before. I don't feel that this is coincidence. With our loads and our rifles using H4350 this equated to 0.5 grains of powder per inch of barrel cut.
    This will probably be different using a different powder/caliber but is food for thought non the less. The data that would be of most interest is the velocity variation and unfortunately i have no access to a chrono.


  9. #9
    Most of my rifles are 20 inches and under. I have had some trouble with 308, moving from 165 grain Federal loads to reloaded Hornady SSTs in the same weight. I am sure that this is down to the ammo rather than the rifle and will be trying more combinations to eleviate this. I have shot a 16 inch LMT rifle recently which was grouping around 250mm at 300 metres with good quality ammo.
    I also shoot a 16 inch barrel 243 which is very fussy about bullet weights and different bullet manufacturers. For what its worth I am about to build at 338 Federal which will have an 18 barrel and my mate uses a 300 Win mag again with an 18 inch barrel.
    For me it's all about the portability and handling of the rifle. If I can shoot a group of 5 rounds at 100 metres that is under 70mm from any position then I now what my limitations are out to 300 metres.
    Just the comments of an old git but hope it helps a bit!

  10. #10
    Thanks all,
    these replys are starting to reasure me that we may not have to much agro if he goes down the shorter barrel route. Parastalker, your observations on powder weight are extreemly interesting, as there are often more than one range of weights within a powder ladder which give a good point for an accurate load development, can I assume that you were fairly close to maximum loads in the first place? have you tried faster powders in your shorter barrel?

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