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Thread: going faster

  1. #1
    Member hntr's Avatar
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    Default going faster

    If I want to sqeeze a little more speed out of a case (300 RUM) do I need a faster burning powder or a slower one. It has a 26 inch barrel. I'm currently using RL 25.

    Another question I have been wondering about. Why is it that a larger caliber bullet in the same case will go faster when using the same weight. 270 vs 30-06 vs 338-06. Is it because of the larger case capacity caused by the larger diameter of the neck? Why should I buy a 270 when a 30-06 will shoot a 130 or 150 grain bullet faster?

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    Good questions all, I think I can help.

    There are three terms that we will use here and each must be understood.

    Time, Pressure and Area, as in how big or circular mill area or square inches area.

    In the same case, and of the same bullet weight, the larger bore will be faster at the same pressure (basicaly we load all modern calibers for bolt action rifles to the same pressure, about 60,000 psi) because; PSI is pounds per square inch and there is more square inches (pi r squared)on which the pressure pushes so it accellerates the bullet more quickly.

    Another way to do this is that in the same case we can get the same velocity with lower pressure with a larger diameter bullet. Which ever way we want to go. Actually we can get some of both, a little less pressure and still a little more velocity, some sort of a compromise.

    Pressure and time, are joined at the hip within the chamber when a round is fired. If the bullet is light weight it gets up and out of the way quickly and pressure will be lower (this all with the same charge weight of same powder burn rate,etc). If the bullet is heavier it will move slower (actually the greater mass has greater at rest inertia and it takes more time to overcome this) and the pressure will have time to build to higher pressure, and it will. For this reason we should go to slower powder burn for heavier bullets.

    With powder burn rate, faster or slower, same charge weight, same case, same bore size, same bullet weight; the faster powder will achieve higher pressure within the confines of the particular rifle, chamber, barrel, etc. Slower powder will give less pressure.

    There also is a direct tie between pressure in any particular firearm and the exit velocity of any particular bullet as you might expect. But, there is no way to ascertain that just because the velocity is lower, the pressure is also lower, it may or may not be. The reverse is also there, higher pressure doesn't necessarily give higher velocity nor is higher velocity a true indication of higher pressure.

    The friction and bearing surface of the bullet, the actual exact diameter of the barrel, the depth and twist of rifling, the actual chamber dimension and the actual burn rate of the powder, (the real time vs pressure curve of that powder lot in that volume, in that rate of confinement, ad infinitum, ad nauseum, etc) all will effect the final peak pressure and the shape of the pressure curve.

    Another really important part is this pressure vs time curve. To plot the curve of pressure, it builds quickly, but takes about 200 to 500 microseconds to reach its peak, but a few thousand microseconds (milli-seconds) to decay back down to exit pressure (generally around 20,000 psi). As we plot this P/T curve it begins to look like a mountain with a steep side on the front and a very shallow slope on the back. The amount of granite in our mountain literally dictates what the velocity will be within a particular firearm/bullet/barrel/ etc combination. To be more specific, it is this area under the curve that does the work or the area under the curve will be velocity within a prescribed set of parameters. (bullet/barrel/etc)

    Slower powders tend to have more area under the curve, as do larger bore diameters, holding our set of parameters, etc.

    In Internal Ballistics we have a couple of terms used to impress the novice.

    Expansion Ratio: The is the ratio of the volume of the swept bore (the part that the bullet travels through) plus the powder volume, compared to the swept bore volume only. Keeping it in the same case, a 264 Winchester magnum has a low expansion ratio, a 458 winchester magnum has a high expansion ratio. (lots of bore volume in which the powder gas can expand) Low expansion ratios need slow burning powder, high expansion ratios use fast burning powder. Your 300 RUM is an exampel of a low expansion ratio. Basically at a glance we can see this by large case, small neck=Low Exp ratio.

    Rate of Confinement: This is an encompassing term that describes the factor that restrict free and easy bullet flight to get out the barrel.
    We use this to describe what effects pressure. Increasing rate of confinement increases pressure. Increasing Rate of Confinement by using a heavier bullet, a faster powder, more powder, heavy crimp, jamming bullet into the rifling, packing snow in the muzzle, shooting a 7mm caliber bullet in a 270 barrel, etc. Obviously going the other way reduces this Rate of Confinement.

    Burn Rate of Powder: This is a generic term used to describe a set of factors that include: the rate of consumption, the yield strength, the type, the differnt coatings, the shape, size and configration of the individual kernals of propellants (smokeless powder) used in modern ammunition.
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    Default Really I was

    I agree those ARE good questions.

    I was gonna say,,,,,
    The slower powder. And because of a flatter pressure curve.

    Because the bullet has a larger base.

    Also, for the same weight, and type of bullet, the larger caliber would have a shorter bearing surface.

    It’s pointless NOW, though.

    Murphy:
    We don’t seem to hear much about ‘bearing surface”, but I figger it has too great an effect to be ignored. I think that some bullets give a higher velocity because of a shorter bearing surface, than another of the same weight. Is it enough to pin down?????

    Also, if you have a bullet length that is barely stabilized with the existing twist, a BT design with less bearing surface can shoot all over the place, when a Flat base will shoot accurately.

    Or so, it has SEEMINGLY worked for me. I would be pleased if you would elaborate on "Bearing Surface", sometime.

    Thanks Even if.
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    Default Wow

    I though I knew a little bit about ballistics and such, but I see compared to Murphy, I'm lucky I know which end of the gun the bullet comes out of!

    I'm going to have to re-read Murphy post a few times, just to absorb all that good stuff.

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    Default thanks Murphy !

    That was the best and simplest explanation I ever read ! My handloading experience is limited but i am getting there ! Kevin

  6. #6

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    Quote Originally Posted by hntr View Post
    If I want to sqeeze a little more speed out of a case (300 RUM)..............
    Call me unfashionable, but I don't worry about dragging the last few FPS out of a cartridge. I don't think anything less than 200 fps change, and in fact I'd even buy 300fps if I thought about it long enough, is significant to the gun's performance on game. You aren't going to be able to see much change in trajectory, or at least not enough to matter on anything bigger than a prairie dog at long range. It's not going to penetrate enough deeper or kill enough faster to make it noticeable either.

    If more than 200fps..... or is it 300fps..... increase is needed, I go to a bigger cartridge to get the extra mileage.

    Less than that, I'm more worried about accuracy and consistency. My 30-06 loads might be going 50fps below max. So what? They might be 150fps below max. Again, so what?

    Do I need 50, 100 or 150fps more than max? Nah. It's not going to push the performance of a cartridge enough above standard to be worth the wear and tear on brass, gun and wallet.

    Do I need 200fps or 300 fps more than max? Then yeah, it's going to show up on the trajectory curve and the impact zone. And I'll go to a bigger cartridge to get it.

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    Member hntr's Avatar
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    Default on performance

    I know speed doesn't matter when putting game on the table is concerned. And I also know that proper bullet placement is the key. I don't think anyone can post a question on this forum without someone chiming in to tell them that.

    Hand loading is a hobby. I had expectations I wanted to acheive with this cartridge and I would like to get there. If it takes some tinkering to do so then all the better. If you had a Hemi in your truck that you were only getting 200 horsepower out of would that be good enough?

    If building model airplanes was your hobby you wouldn't stop building the thing before it flew would you.

    I figure If I wanted to just lob 180 grain slugs I could do that with my 30-06.

    Thanks Murphy, I appreciate the knowledge you are willing to share with everyone on this forum.

  8. #8

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    Quote Originally Posted by hntr View Post
    I know speed doesn't matter when putting game on the table is concerned. And I also know that proper bullet placement is the key. I don't think anyone can post a question on this forum without someone chiming in to tell them that.

    Hand loading is a hobby. I had expectations I wanted to acheive with this cartridge and I would like to get there. If it takes some tinkering to do so then all the better. If you had a Hemi in your truck that you were only getting 200 horsepower out of would that be good enough?

    If building model airplanes was your hobby you wouldn't stop building the thing before it flew would you.

    I figure If I wanted to just lob 180 grain slugs I could do that with my 30-06.

    And that's the spirit! I gotta test all the angles and search for the best possible combo, or else I'd be content with factory ammo. You're exploring what you can achieve with your gun. But I know a couple of guys that sold perfectly good rifles at deep discounts (to me, as a matter of fact) because they didn't shoot well at "book" max.

    One was a virtually new Ruger M-77 in 300 Winnie that "only" hit 3100 with its most accurate load for a Partition 180. Since my 06 was "only" delivering the same bullet at 2700, the 400fps seemed like a pretty good reason to spend $300 on a virtually new rifle.

    Then I let my son-in-law talk me out of the 300 and I went back to shooting the 06. Dang his hide anyway! The loss of 400fps hasn't cost me any game but I sure did enjoy shooting that 300. And enjoying shooting it is plenty of reason for me to try talking him into selling it back. Not a chance, sezz he!

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    Quote Originally Posted by hntr View Post
    I know speed doesn't matter when putting game on the table is concerned. And I also know that proper bullet placement is the key. I don't think anyone can post a question on this forum without someone chiming in to tell them that.

    Hand loading is a hobby. I had expectations I wanted to acheive with this cartridge and I would like to get there. If it takes some tinkering to do so then all the better. If you had a Hemi in your truck that you were only getting 200 horsepower out of would that be good enough?

    If building model airplanes was your hobby you wouldn't stop building the thing before it flew would you.

    I figure If I wanted to just lob 180 grain slugs I could do that with my 30-06.

    Thanks Murphy, I appreciate the knowledge you are willing to share with everyone on this forum.
    I wanted to answer your questions and hope I did, except I didn't mention any slower powders. Often when I read these posts about certain calibers it it's difficult to suppress my own opinion. What I gave you had nothing to do with my opinion, just the facts, and a little razzle dazzle for effect. I do understand what you're after I have been there but I wouldn't want to deprive you of your own experience and learning.

    My opinion based on my experiments with so many different cases and calibers leads me away from what you want to do. But that isn't my cup of tea nowadays. I just to say that the huge RUM case cannot be filled with any available powder so it must be too big. It of course will give higher velocity than any other smaller case but the efficiency of it is highly degraded. Sometimes we don't care how efficient something is we are after a certain level of performance. I think what BrownBear was saying is that, from a practical field performance perspective, the extra velocity has no real benefit. I agree with that other than to say velocity and flat trajectory go hand in hand. Since I have done some long shooting I understand the desire (not need) for the extra velocity. Here again the terminal advantage (what the bullet does after it gets there) will be minimal and may be a disadvantage under some circumstances. But you have your own plan.

    I did some loads with Retumbo and Magnum (think that's is Accurate [AA] Powder). They are both slower than RL-25. It seems my accuracy was best with RL-25 except for the 200 to 220 grain bullet weights. I think Retumbo will be the best all round powder and it will load with a few grains more than RL-25. Like I said though nothing is slow enough but the slower the better in that case.
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  10. #10
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    I'm happy with the rifle and have an accurate load that moves pretty good, I just want to see if I can get a noticable improvement from a faster or slower powder.

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    Moderator Paul H's Avatar
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    You can't always get more velocity by going to a slower powder, because at some point you can't fit enough of the slower powder in the case to get to peak pressure.

    There is also a point of diminishing return in the large case small bore rounds. You can increase the case capacity by 10%, and may only increase velocity 1%.

    The best way to gain velocity is to install a longer barrel. Back to your hemi analogy, if your tires are too skinny, you can't put the power to the ground. In this case, if your barrel isn't long enough, you can't burn effectively burn the extra powder the case holds.

    And if you don't want to go to a longer barrel, go to heavier bullets. To me the advantage of the large cased rounds is the ability to shoot heavier high bc bullets at noteably higher velocity than the smaller cased rounds.

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    Default This makes me wonder myself

    I agree with Brownbear, about dragging the last FPS out of a cartridge. (I read in a loading manual, maybe the Lyman, that when you are on on the ragged edge of maximum pressure, the least little thing can send pressure out of control.)

    Also, if I can get within 50 fps of the FL velocities, I'm happy. However, for some reason, I've always considered 100 fps to be a significant difference in velocity.

    To my way of thinking, large cases are for heavy bullets, and slower powders. It seems pointless for terminal performance, or even trajectory, to go with a short light bullet, because the first is risky, and the second is dubious.

    I suppose someone invested in a 300 RUM, would be motivated to get MORE, to justify the extry powder and recoil, if nothing else, and even be interested in which powder would accomplish that.

    Keep it comin. I'm readin it.

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  13. #13

    Default Just my experience

    I personally had best luck with retumbo with 165 and 180 grain bullets.
    I found H870 to be best with the 200 and 220's, although retumbo was close with the 200 grain bullets too.

    165 @ 3500-3550
    180 @ 3300-3400
    200 @ 3150-3250
    220 @ 3050-3150

    Depending on bullet make.

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    Unfortunately as the pressures begin to climb, gasses begin to behave like liquids. At a point, no increasing pressure will increase the velocity of the projectile, due to restrictions in flow.

    The example is the .264 Winnie, the 6.5-.300 Weatherby, 6.5-300 Winnie and the 6.5-378 Weatherby.
    .264 Win will get you 3100 fps with 140 grain projectile and 26" barrel.
    The rest will give you 3450 fps with 140 grain projectile and much more powder and 26"-30" barrels. Odd isn't it? All about flow and area.

    Now take the 120mm rifle used in the M1 Abrahms. The sabot version can run near 5100 fps, right on the edge of the terminal velocity for gas (roughly 5200fps). Odd isn't it? All about flow and area.

    All of this at the same pressures. Doesn't matter if it is the .14 Flea or the 16" rifle of the Iowa Class battleships, they all obey the same laws.
    Great spirits have always found violent opposition from mediocre minds. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices but honestly and courageously uses his intelligence. Albert Einstein

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    Hey Cedar, you've sucessfully posted here 6 times and after reviewing your posts, you haven't had that much to say. Lets keep the cynical remarks to a minimum and actually try and help some people out. If you know about a certain topic, by all means spread the wealth of knowledge, but if you're going to just bash people and make silly posts, it'd be best if you take it elsewhere. Thanks

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    Quote Originally Posted by Cedar Swinger View Post
    You find (1) inaccuracy on my part.

    Until then...take notes.
    Point proven....thanks....

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    Quote Originally Posted by Cedar Swinger View Post
    You find (1) inaccuracy on my part.

    Until then...take notes.
    Incorrect. More than two.
    Great spirits have always found violent opposition from mediocre minds. The latter cannot understand it when a man does not thoughtlessly submit to hereditary prejudices but honestly and courageously uses his intelligence. Albert Einstein

    Better living through chemistry (I'm a chemist)

    You can piddle with the puppies, or run with the wolves...

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