Understanding shotgun Ballistics

Discussion in 'Large-Bore/Small-Bore Rifle/Shotgun' started by Rommelvon, Feb 9, 2008.

  1. Rommelvon

    Rommelvon New Member

    Aug 6, 2006
    Goldsboro, NC
    First, the drams equivalent printing on the boxes and the shells do not mean that shotshells actually hold that much powder. If they were in fact loaded with such heavy charges of smokeless powder, they would be little sticks of dynamite! Thus, don't even bother about drams as a modern measurement for smokeless powder.

    The key here is the word "equivalent," which simply means that the load is equal to the performance of an old black powder load with a certain amount of powder as measured by the drams (avoirdupois) method. Modern smokeless powder is so much more powerful than black powder than any reloading by drams with smokeless will result in dynamite.

    What "drams equivalent" really means is that this particular smokeless powder load has the same approximately velocity as a black powder loading with the stipulated number of drams. A modern 3 drams equivalent trap load with 1-1/8 ounces of shot, for instance, has a muzzle velocity of about 1,200 f.p.s., which is roughly what the older black powder loads churned up with a powder charge of 3 actual drams of black fuel. Thus, the drams equivalent designation is merely a comparison of velocities--definitely not a comparison of powder charge weights!

    Today, our method of measuring shotshell powder rests with the "grain" as a basic unit of weight. There are 437.5 grains per ounce, and there are 7,000 grains per pound.

    On the other hand, in the avoirdupois method of measuring weights, there are 16 drams per ounce and 256 drams per pound. That means the dram is heavier than the grain, and mixing them up is dangerous. When a beginning handloader mentions a dram instead of a grain, correct him immediately! The dram is no factor in scaling smokeless powders.

    Let's carry this explanation one step further and elaborate upon some of the specific shotshell loadings and their references to, and comparison with, the old black powder rounds. These drams equivalent stats are based upon a black powder shotgun's performance with FFg and are normally equated with chronograph readings taken three feet from the muzzle.

    In the popular 12-gauge, there are two 1-1/4-ounce loads: one is a 3-1/4 drams equivalent package; the other, a 3-3/4 drams equivalent load. The 3-1/4 drams rounds, often known as the "live pigeon" load, have a normal velocity of 1,220 f.p.s., while the 3-3/4 drams equivalent one runs about 1,330 f.p.s.. When we switch to modern smokeless powders, however, the 3-1/4 drams equivalent reload can be made with a significantly lighter powder charge like this:

    Federal Gold Medal hull

    Federal 209 primer

    24.0 grainsof Unique

    Federal 12S3 wad

    1-1/4 ounces of lead shot

    Pressure: 10,500 p.s.i

    Velocity: 1,220 f.p.s.

    That 24.0-grain charge of Unique doesn't yet scale 1 gram; however, it generates as much velocity as a whopping 3-1/4 drams of FFg black stuff. (There are 27.34 grains in a gram.) Thus, we have a good example of the energy in smokeless as compared to black powder.

    The 3-3/4 drams equivalent 12-gauge load with 1-1/4 ounces of lead shot has long been a favorite, and at one time was the outstanding duck load, known as the "high brass" or "high velocity" load. It used another half gram of FFg black powder than did the 3-1/4 drams equivalent, and it impressed shooters with its speed of more than 1,300 f.p.s. Today, we can get that same velocity level with much less powder, such as:

    Winchester AA hull

    Winchester 209 primer

    34.0 grains of Hodgdon HS-6

    Remington R12H wad

    1-1/4 ounces of lead shot

    Pressure: 10,300 l.u.p.

    Velocity: 1,330 f.p.s. (nominal)

    That 34.0-grain charge of HS-6, if it were converted to drams, would be about a 1-1/4 dram charge in actual weight. I must stress again, however, that this is just an example; modern smokeless powders aren't metered out in drams per se. The term we are working with is "drams equivalent," and it is simply a comparison and not to be used as a de facto reloading figure with smokeless powders. The increased potency of modern smokeless powders puts more energy into lighter charges, and there is no easy comparison between the old drams figures and the newer ones based on grains of powder. They are nothing more than velocity equivalents.

    The shooting industry, with SAMMI (Small Arms and Ammunition Manufacturers Institute) as the repository for standards, has established a list of standards for shotshells of one drams equivalent rating or other. Here, by gauge and hull length, is the most recent list. It shows the nominal launch velocity for each drams equivalent level common to today's market. Realize, of course, that all loads will show some variations upon testing; nothing is perfect except scientific theory.

    10 Gauge

    2-7/8" Hull

    Drams Shot
    Equiv. Charge Velocity
    (oz.) (f.p.s.)
    4-1/2 1-5/8 1,330
    10 Gauge

    3-1/2" Hull

    4-1/2 2 1,255
    4-1/2 2-1/4 1,210
    12 Gauge

    2-3/4" Hull

    3 1 1,290
    2-3/4 1-1/8 1,145
    3 1-1/8 1,200
    3-1/4 1-1/8 1,255
    3-1/4 1-1/4 1,220
    3-1/2 1-1/8 1,310
    3-3/4 1-1/4 1,330
    3-3/4 1-1/2 1,260
    12 Gauge

    3" Hull

    4 1-5/8 1,280
    4 1-7/8 1,210
    16 Gauge

    2-3/4" Hull

    2-1/2 1 1,165
    2-3/4 1 1,220
    2-3/4 1-1/8 1,185
    3 1-1/8 1,240
    3-1/4 1-1/8 1,295
    3-1/4 1-1/4 1,260
    20 Gauge

    2-3/4" Hull

    2-1/2 7/8 1,210
    2-1/2 1 1,165
    2-3/4 1 1,220
    2-3/4 1-1/8 1,175
    20 Gauge

    3" Hull

    3 1-1/4 1,185

    28 Gauge

    2-3/4" Hull

    2-1/4 3/4 1,295
    2 3/4 1,200(Skeet)
    2-1/4 7/8 1,250
    2-1/4 1 1,205
    (The .410 bore is not listed in drams equivalent values.)

    Thus, we have the nominal muzzle or launch velocities for each gauge according to its hull length and shot charge weight for each drams equivalent rating.

    If a customer comes in and says he's impressed with a certain 3 drams equivalent 16-gauge load he's using and would like to reload some akin to it, you can dig out this list and tell him it's a basic 1,240 f.p.s. velocity load with 1-1/8 ounces of shot. Then you can refer to the current reloading data and locate a similar combination, although the current data is stated in terms of grains of powder to achieve any velocity level. Once you know the velocity, the rest is easy.

    If somebody is still confused, just tell him that the "drams equivalent" designating means the amount of FFg black powder that would normally have been used to develop the same velocity level for that particular load. Tell him it has nothing to do with the reloading of smokeless powders. Tell him it is actually an archaic way of doing things, and that the drams equivalent markings should probably have been dropped back around WWII and replaced by a simple, albeit nominal, velocity reference for far less confusion and much greater clarity among typical and casual hunters.

    What are some effective velocity levels for the various shotgunning sports? For clay target shooting in American-style skeet and trap, we're learning that 1,050 to 1,200 f.p.s. is an effective range; in fact, the newer commercial "lite" loads are operating from 1,125 f.p.s. down to 1,075 f.p.s., and people find they can score perfectly with them while feeling no objectionable recoil.

    For upland hunting, a velocity range of 1,165 to 1,255 f.p.s. is good, with an emphasis on 1,200 to 1,255 f.p.s. In steel shot, I'd suggest all the speed one can get; the range of 1,300 to 1,425 f.p.s. is nominal today, and those of 1,365 to 1,425 f.p.s. carry the greatest energy to high birds.

    For sporting clays, anywhere from 1,200 to 1,300 f.p.s. seems fine, depending on the individual person and his ability to take recoil. I frankly can't see where we need anything beyond 1,200 to 1,250 f.p.s. for sporting clays, which is turning into a close-range game stateside.

    Some of your customers will want nothing more except souped-up shotshells. "How do we get more velocity?" they'll ask. Unfortunately, they don't comprehend the significance of the "f.p.s." values, and anything below, say, 1,300 f.p.s. doesn't appeal to them. Perhaps you can impress them by converting feet-per-second into miles-per-hour, which can be done with simple math: begin with the velocity in feet-per-second and multiply that by 60 to get feet-per-minute. Then multiply that result by 60 again to get feet-per-hour. Now divide that by 5,280 (the number of feet-per-mile) to get the shot load's speed in m.p.h.

    For example, a lowly trap load doing 1,145 f.p.s. is actually leaving the muzzle of a 30" barrel at 780 m.p.h.! That's impressive. And crank that to a "heavy" trap load with 3 drams equivalent of powder for 1,200 f.p.s., and we get 818 m.p.h. Federal's 2-3/4" 20-gauge load of steel (3/4-oz.) does about 1,425 f.p.s. converts to about 975 m.p.h.

    The 3" .410's long 11/16-oz. load does only about 1,135 f.p.s., and velocity "nuts" hold their noses. But even that calculates to 774 m.p.h.--which will win the Indy 500 any day!

    Thus, shotgun ballistics are all a matter of knowing the terminology and somehow putting them into practical concepts. Except for steel, where I believe high speed is essential, beginners often put too much importance on velocity and not enough on pattern.
  2. bluesea112

    bluesea112 Active Member

    Nov 20, 2005
    West, TX
    Wow! Thank you for that information. I am just getting into shotgun reloading, and this information helped me a lot. It is good to know "why", and not just the "how". Thanks for taking the time to post this!
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