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Fast vs. slow powders

Discussion in 'Handloading and Reloading' started by 0to60, Jun 23, 2013.

  1. 0to60

    0to60 Well-Known Member

    I'm confused. Fast powders burn quick with a peaky pressure spike. Slower powders have a flatter pressure curve, imparting more energy to the bullet while never reaching the pressure peak of a fast powder.

    So why would we ever use a fast powder? It seems to me that the best possible powder would be one that finishes burning just as the bullet leaves the muzzle. If the charge is complete before the bullet leaves the muzzle, then there was some wasted time where "work" could have been done. If the charge hasn't finished burning by the time the bullet leaves the muzzle, then you have wasted powder.

    It would seem that fast powders should be used in short barreled guns. I never hear that, though. Whenever someone asks a "what's the best load for..." question, I don't see people asking for barrel length.
  2. zxcvbob

    zxcvbob Well-Known Member

    The slowest-burning powder that reaches full pressure (like W296 in a magnum revolver cartridge) will always give the highest velocity; doesn't matter if it's a long barrel or a short barrel. It may take 2 or 3 times as much powder to do it (all barrel lengths) And in a short barrel, the velocity gain might not be very much.
  3. maxyedor

    maxyedor Well-Known Member

    At the end of the day, a good powder for ______ round, is a good powder for that round no matter the barrel length. Generally speaking anyway.

    IMHO, it's best to give a somewhat general answer to a general newbie question like "What's the best powder for .357?". The reality is, the perfect powder for a 1.5" barrel revolver and a sixteen inch barrel lever gun are very different powders, but a "good" .357 powder at a moderate load will work well in either.

    Once you get more advanced with your reloading, you can start to consider barrel length, and tune you powder choice accordingly.
  4. bds

    bds Well-Known Member

    For lighter target loads.

    IMHO, slower than W231/HP-38/Unique powders tend to produce optimal accuracy at high-to-near max load data from more consistent chamber pressures/powder burn but if you want to use lower velocity target loads, the powder won't burn as clean and chamber pressure build up may get inconsistent resulting in decreased accuracy.

    Most of my 9mm/40S&W/45ACP range practice/plinking loads use mid-to-high range load data with W231/HP-38 and faster burn rate powders and some loads at start-to-mid range load data that still produce accuracy.

    Light 40S&W target load:

    Let's say you want a light recoiling lower pressure 40S&W load (actually, my sister recently made such a request). So for my range trip today, I loaded up the following to test (all rounds were loaded at 1.125" OAL):

    - 165 gr Montana Gold JHP with 4.8 and 5.0 gr of W231/HP-38
    - 180 gr X-Treme plated FP with 4.2 and 4.5 gr of W231/HP-38

    I used the following Hodgdon load data:
    Range test results:

    165 gr JHP: 5.0 gr mid range load is my range load and as anticipated, reliably cycled the slides of G22/G23 and was accurate. 4.8 gr start charge load also reliably cycled the slide and was accurate (all test shots off hand were inside 1/2 sheet of 8.5x11 copy paper target at 7-15 yards).

    180 gr plated FP: 4.2 gr is 0.2 gr below start charge but still reliably cycled the slides of G22/G23 and was accurate. 4.5 gr is my typical range load (essentially a start charge load) and as anticipated, reliably cycled the slide and was accurate (all test shots off hand were inside 1/2 sheet of 8.5x11 copy paper target at 7-15 yards).

    How many slower burning than Unique powders will reliably cycle the slide and produce accurate target loads at start charges? :D

    Light 45ACP target load:

    Promo/Red Dot are faster burning than W231/HP-38 but I use them for even lighter recoiling plinking loads. With 200 gr MBC SWC bullets (18 BHN IDP #1 and 12 BHN Bullseye #1), I use 5.0 gr of W231/HP-38 which is a mid range load that is accurate and doesn't lead the barrel.
    I referenced 2004 Alliant load data and used Red Dot load data for Promo as indicated by Alliant - http://www.alliantpowder.com/products/powder/promo.aspx


    4.0 gr of Promo/Red Dot with 200 gr SWC bullets produce a lighter recoil load that still reliably cycles the slides of various 45 pistols and produce accurate shot groups without leading.
    Last edited: Jun 23, 2013
  5. Lost Sheep

    Lost Sheep Well-Known Member

    Fast powders give lower ultimate velocities. This is part of the reasoning, too.

    This is my speculation, fueled by all I have heard, read and experienced. So, I believe it is correct.

    All smokeless powders operate in a reasonably narrow pressure range. Fast powders get up into that range with very little charge weight and then fall off quickly because they run out of propellant. With more propellant, pressure would quickly surpass most firearms ability to survive.

    Slower powders (since they occupy more volume, leave less free space for expansion, also get up into that range pretty quickly, but then their slower burn rate puts a limit on the peak pressure attained. But they maintain that pressure for a longer period of time, thus attaining more ultimate velocity with the same peak pressures.

    If you want moderate velocities, you use a faster powder. If you try to get moderate or low velocities with a slow powder by using a lighter charge, you never get up into the powder's optimal operating pressure. Without being in that pressure range, burn rate is erratic. Sometimes you get a stuck bullet. Sometimes (now, this is controversial, because some people believe it cannot happen while others do believe) you get a phonomenon known as "flashover" or "detonation". Then there is the even more controversial, unpredictable and less understood effect known as S.E.E. (secondary explosive effect).

    Low charges are tricky and as dangerous as high charges.

    Like I said, this is speculation on my part. But informed by all I have heard and read.

    Lost Sheep
  6. morcey2

    morcey2 Well-Known Member

    Whether the powder is fast or slow, it's burned as much as it's going to by the first inch of bullet travel. It doesn't burn during the entire time that the bullet is traveling down the barrel. One reason to use fast powder is the difference in the amount of powder needed for a specific velocity. I've got a couple of 30-06 loads that both shoot at about 2900 fps with 150 grain bullets. One (my most favoritest) is 52 grains of IMR-4064. The other is 58 grains of H4350 (I think it's 58 grains. Might be 57. My notes aren't available at the moment.) Both shoot very well and are accurate in my sportered 1903. But I can get about 10% more loads from a pound of 4064 as opposed to 4350.

    Most of the time, you need to let the gun tell you what it likes. Some will shoot well with anything. Another one will tell you it likes a specific powder, bullet type, even a specific primer.

    Another place where fast powders shine is in reduced loads. An extreme example of this is "The Load" with 13 grains of Red Dot under average-weight bullets in rifle cartridges. Very fast powder and a good plinking load. Hodgdon has some specific reduced loads for H4895 and according to their research and testing, it's the slowest powder that can safely be reduced significantly. Slow powders can't be reduced without risking inconsistent ignition or something called Secondary Explosive Effect. I don't quite understand it, but it results in an extremely dangerous overpressure condition that can severely damage guns and shooters.

    Related to reduced loads is the fact that the slower the powder, the harder it is to ignite consistently.

    Velocity isn't everything. A really fast bullet isn't much use if it's not on a reasonably predictable path to the target.

    Enough of my late-nite ramblings.

  7. ljnowell

    ljnowell Well-Known Member

    It should be mentioned that some powders, like w296 for example are incompatible with certain cartridges such as 45acp. By the time it reaches sufficient pressure to burn properly its overpressure for the cartridge. It simply will not work.

    Lower pressure cartridges require faster burning powder, higher pressure cartridges can be "downloaded" with fast pressure but require slower powder to perform at their optimum level.
  8. Steve C

    Steve C Well-Known Member

    Fast and slow powders are relative to the cartridge case volume, pressure and the bullet weight. Unique is considered a mid range burn rate for handguns but is a bit fast for a 50 S&W mag and a relatively slower powder for the .32 caliber guns and others cartridges with small case capacity.

    In general fast powders are used for economical lower velocity target loads while slower powders are used to maximize velocities in self defense and hunting loads.
  9. gamestalker

    gamestalker member

    Good question. Here's some primary example's of why I like to use slow burner's exclusively, in that, I only load jacketed bullets, I like full tilt or some where near, and I don't like to work with powders that have short loading tables. Some other advantages to using slow burner's for me personally is, I like powders that fill the case because they can make accidental double charges impossible in many instances, and increments of one or two tenths don't create severe pressure issues during work up. And in my opinion, I also think that slow powders are easier on the firearm, even when pushing velocities equal to, or quicker, than a fast burner at mid to top end data. But that is only my opinion, and there probably isn't any supporting facts that back that opinion.

    There is absolutely nothing wrong with faster burning powders for use with jacketed bullets, I just don't care for what I consider pins and needle work ups do to how pressure sensitive they can be when approaching red line, or when working near the bottom line due to an increased risk of sticking bullets in the barrel, but that's me, and I surely don't represent the majority, in my opinion. If I had to guess though, I would say 9 of 10 reloaders I know or have known load exclusively with fast burners, usually because they are much more economic to load with, and also because they are perfect for loading light target loads cause they can be manipulated at the lower end of the charge table with few to no issues. But I would also guess that more catastrophic issues have occurred with fast burners, either because of double or triple charges slipping by unnoticed, and stuck bullets causing KB's from under pressured loads sticking a projectile in the barrel that got over looked by the shooter.

    Slow burners are typically incapable of loading light target loads with and often perform very poorly when attempting to due so, producing inefficient burns, and producing inconsistent velocities and pressures when taking them down to, or below starting charges.

    Just my two cents worth, for what it's worth.

  10. jim243

    jim243 Well-Known Member

    What was said above.

    Short answer:

    Fast Powder - lower pressure slower bullet.
    Slow Powder - Higher pressure faster bullet.

    Example - 38/357 uses the same bullet.

    Fast Powder - 38 Special (Win 231 powder)
    Slow Powder - 357 Mag (Alliant 2400 powder)

  11. zxcvbob

    zxcvbob Well-Known Member

    Fast powder does not necessarily mean low pressure. (it does mean the area under the pressure curve will be less) For the *same* pressure, a fast powder will use less powder than a slow one and result in a lower velocity. ETA: it will not necessarily be much lower in velocity
    Last edited: Jun 23, 2013
  12. jmr40

    jmr40 Well-Known Member

    Primarily from a rifle shooters perspective.

    Fast and slow powders will burn within the 1st few inches. Pressure continues to build and velocity still increases as long as the bullet is still in the barrel. At least with reasonable length barrels. I suppose with a barrel long enough you will start to see speed decrease with the bullet still in the barrel. Whatever powder gives you the best velocity from a longish barrel will also be the fastest from a short carbine length barrel. But if you change bullet weights, you may need to change powder for optimum perfromance.

    The chambering and bullet weight determine which is best for bullet speed and accuracy. A 308 with 150 gr bullets will get optimum bullet speeds and accuracy with powders slighty faster than the same powder in a 30-06 with the same bullet weight. The same 30-06 powder that gives the best speeds with 150 gr bullets may prove to be a poor powder when you move up to 180-200 gr bullets.
  13. beatledog7

    beatledog7 Well-Known Member

    In case it has been missed, there is also an economics consideration.

    If one loads .45ACP with a fast powder such as W231, he can probably achieve reliable function and good accuracy at about 750FPS with just 4.2 grains of powder. If he chooses HS-6, a much slower powder, he's going to need almost twice as much (8.2 grains per Hodgdon) powder to achieve similar function and velocity (only 40FPS faster) results.

    At $25/lb, one round of .45ACP would use 1.5¢ worth of W231 or 2.9¢ worth of HS-6. That adds up if you're a volume reloader.

    True, one might have a specific reason for choosing a slower powder, but for the most common purposes, the factor that is likely to matter most is cost. If one loads 2,000 of the above rounds with the faster powder, he saves more than enough in the cost of powder to buy another pound.
  14. Magnum Shooter

    Magnum Shooter Well-Known Member

    Actually the question of barrel length is asked in a roundabout way. The difference between a 3,4,5, or even 6 inch barrel is not that much, but the difference between a 6” handgun and a 20” rifle is. Rifles use slower powders than handguns.
  15. brickeyee

    brickeyee Well-Known Member

    You have to understand tat the 'fast' and 'slow' are relative terms.

    A 'fast' pistol powder may have finished breakdown from solid to gas before the bullet has moved its own length (or left the case).

    A 'slow' rife powder might still be breaking down when the bullet is a few inches into the barrel.

    Fast and slow refer to time to peak pressure.

    They say nothing about the area under the time-pressure curve as the bullet travels down the bore.

    THAT area is what determines muzzle velocity.

    Peak pressure blows things up, average pressure gets you high velocity.
    Last edited: Jun 24, 2013
  16. bds

    bds Well-Known Member

    I agree with you on the bulkier powder overflowing the case with a double charge. But so can some fast powders like Red Dot and Promo which are very fast but the flakes are large and bulkier than Unique. Double charge of most Red Dot/Promo loads will overflow 9mm/40S&W cases and come close to full in 45ACP cases to notice when placing the bullet (you would need to compress the powder charge to seat the bullet).

    Below is a comparison picture of 45ACP loads for 185 gr Remington Golden Saber JHP bullet. 45ACP case capacity is about 14 gr for Promo and 12.5 gr for Red Dot. While a Red Dot double charge of almost 12 grains would not overflow the case, the powder would be almost to the top of the case and seating a bullet would be difficult.

    40S&W case capacity is about 10 gr for Promo and 9.5 gr for Red Dot while 9mm case capacity is about 7 gr for Promo and 6.5 gr for Red Dot. Double charges of typical 9mm/40S&W Red Dot/Promo loads would likely overflow cases or make seating a bullet difficult.


    I would mostly agree but in semi-autos pistols, under pressured loads (say a few tenths of grain below start charge) will still push the bullet out the barrel - it's the squib rounds that will stick a bullet in semi-auto barrels and that could happen with any burn rate powder.

    I think both fast and slow powders have their place in reloading to meet the individual reloader's needs whether it's more velocity, less recoil, double charge detection, cleaner powder burn for easier pistol cleaning, flexibility to load multiple calibers, cost savings, etc.:

    - If you want full power pistol loads with highest velocities, go with slower powders.
    - If you want lighter recoil lower pressure target loads that are still accurate, go with fast powders.
    - If you want powders that will overflow a case with a double charge, go with bulky powders.

    As others posted, use of faster powders for target loads work for rifles too. Hodgdon offers reduced rifle loads using H4895 and reduced rifle loads using Trail Boss which are relatively fast powders compared to slower rifle powders.
    Last edited: Jun 23, 2013

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