powder charge vrs barrel length

Discussion in 'Reloading' started by RustyRick, Aug 11, 2013.

  1. RustyRick

    RustyRick Well-Known Member

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    It seems most loading data is done in a long barrel like at least 24 inches. So obviously a shorter barrel needs a smaller than posted load or else your buying powder and blowing excess out side the barrel.

    So it's logical a 18.5 inch barrel definitely need lighter loads.

    Any thoughts on how much lee one should de-rate the book values based on barrel length?
     
  2. trophyhusband

    trophyhusband Well-Known Member

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    What about using a faster burning powder?
     

  3. g0rd0

    g0rd0 Well-Known Member

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    in a way you are correct. But, the proper way to choose powder is by expansion ratio. A bit complicated to understand but here is the short version, case capacity + caliber + barrel length (barrel length is the distance from the base of the seated bullet while in the chamber to the muzzle, not the listed length from the manufacture, this is measured useing a dummy round). Once you know your BL, CC and caliber from a chart or slide rule you can determine your burn rate and that is how choose your powder.
    If what I have just posted sounds greek to you then use your books and publications, always confirm your load, start with the start load, load 5 then load 5 each of .5 grain incraments untill you get to the max load. go to your range and at 100 yards from the start load fire your 5 shots, (dont worry if the sights are a little off you are interested in groups at this point) take note of the size of the group and signs of preasure. Then do the same for the next incrament and the next ect. untill you notice the tightest group. You then have the most efficiant load combo of that powder and bullet for that rifle.
    The books list 150 grain bullet in a 7mm rem mag useing IMR7828 SS, 63.4grn max 68.7 the vel 2851 to 3100fps. In my savage the tightest group is at 67.0 grns chrono at 3010fps so that is where I keep it.
     
  4. RustyRick

    RustyRick Well-Known Member

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    Ya I realize that principle. However my question is that if the recommended load is 54 gr of 4831 in a 24 inch barrel. An 18.5 inch carbine should discount the data to a lesser load so as not to finish burning the powder out side the muzzle.
     
  5. benchracer

    benchracer Well-Known Member

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    There is no need to lighten your load to compensate for a shorter barrel. Likewise, going with faster powder in a shorter barrel will do nothing for you.

    I know it seems counter-intuitive, but the way to maximize performance in a short barrel is to go with heavy for caliber bullets and slow powder. The key to the whole thing is pressure rise time. A heavy bullet will help build pressure sooner by providing more resistance. If you can put together a combination whose optimum burn rate range is in the neighborhood of the 4350 type powders, you can benefit from the steeper pressure rise of powders like RL-17.

    The current crop of factory ammo from Hornady in the Superformance line and in chamberings like 6.5 Creedmore, .375 Ruger, and the Ruger Compact Magnums all take advantage of the fast rise time available in some of the newer powder formulations to deliver excellent performance from short barrels.

    Unfortunately, the powders they use are not currently availabe to handloaders.
     
    Last edited: Aug 11, 2013
  6. g0rd0

    g0rd0 Well-Known Member

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    if you cannot understand that a load below sugested start is capable of produceing unsafe preasure than you donot understand basic safety.
    Read the manuals, never go below start and never go above max. If you choose to ignore this then it is only a matter of time till your favorite rifle, shotgun or handgun goes boom in a very unpleasant way.
    And never under any circumstance use any load that you get from here or anywhere else untill you are able confirm it by a differant sourse. And that goes for everybody's load datta, be it Layman, Lee, Speer, Alliant, Hornady, Nosler and any other publication (includeing me!).
     
  7. trophyhusband

    trophyhusband Well-Known Member

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    Thanks for the explanation. There's certainly a lot more to this stuff that I realized when I started reloading.
     
  8. trophyhusband

    trophyhusband Well-Known Member

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    Can you expand on that a little? Also, different manuals suggest different starting loads and different max loads. How do you determine where the upper and lower limits really are?
     
  9. flashhole

    flashhole Well-Known Member

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    This is an interesting topic and different flavors of it have been debated many times. Frow what I've read, the consensus is - efficiency of a load developed for a long barrel is generally the best for shorter barrels too.

    Direct experience - I've found this to be the case for the 45-70. Loads proven best when used in a long barrel High Wall were also the best for my Guide Gun.
     
  10. benchracer

    benchracer Well-Known Member

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    That's a very succinct way of putting it and spot on, IMO.
     
  11. RustyRick

    RustyRick Well-Known Member

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    Thanks for some good insights! I'm using a 6.5 Rem Mag and my new manuals don't have any data for that wonderful Cinderella caliber. It's in a Rem 660 with an 18.5 inch barrel.
     
    Last edited: Aug 11, 2013
  12. RustyRick

    RustyRick Well-Known Member

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    Thinking - I can see the accuracy being the same for the short barrel as well as the long one with the same powder and load.

    But my logic says that a bunch of un-necessary powder is burning out side the muzzle.

    To use 24 inch data in an 18.5 inch barrel seems illogical.

    But I guess I'll shed some light on it personally as I work up some roll-yer-own recipes for this 6.5 that was handed to me.

    I'm going to try my first batch with 5 groups of 3 shots with 140 gr. Hornady and 4831, 4350, & H380.
     
  13. Bart B

    Bart B Well-Known Member

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    I believe that a good load will have uniform pressure curves so the muzzle velocity spread's small regardless of barrel length. Therefore, I don't think there would be any difference in accuracy. But trajectory's will be flatter with longer barrels. Of course the barrels will whip and vibrate differently but each one's repeatable for each shot in the frequencies and amplitude they have. As long at that happens, it doesn't matter when the bullet leaves the barrel; 22 or 28 inches from the bolt face.

    Proof of this to me is folks shooting Federal Gold Medal .308 Win. match ammo in N14NM rifles' 22 inch barrels as well as bolt action match rifles with 28 inch barrels. Both produce the same accuracy level at 600 yards; about 2/3 MOA at worst. If I'd not seen this done in a 600 yard match, I would not have believed it. Later proved it to myself by shooting my own lot of that ammo type in a borrowed M14NM and my 28" barreled match rifle. Both had 1:11 twists and virtually the same bore and groove dimensions within 1/10,000th inch.

    Rusty Rick, you'll get a much better idea of accuracy with those loads shooting one 15-shot group with each load. If you shoot five 3-shot groups and they're not all within 10% of the same size, they don't reflect what the real accuracy they have is. You can shoot five 3-shot groups on each of 5 targets laid over another one to capture all 15 shots. Doing this usually surprises folks when they see each of their five 3-shot groups being smaller than the 15-shot composite.
     
  14. Canadian Bushman

    Canadian Bushman Well-Known Member

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    Rusty rick, your logic is sound, but maybe you can try to see this from another view. Very few rifles actually burn all the powder before the bullet leaves the barrel. Thus the muzzle flash. Most reloaders dont worry about this but are more concerned with the overall performance of how their reloading componets work together. Like bart said, a consistant pressure curve that moves the bullets into the rifling and down the bore in a speedy, safe and consistant matter is where accuraccy and speed come from. A longer barrel is like a plus because you can stretch that pressure out and get a little more speed for a given load. I personally dont care how much powder i burn outside the barrel, so long as i get good consistant velocities without over pressure.