Based on my qualitative analysis backed up by rudimentary quantitative analysis I am coming to believe that muzzle velocity higher than the speed of sound for small spheres is counterproductive. There is an increase in recoil for an undetectable increase in on-target power.
For, say, shot sizes BB and smaller the ballistic coefficients are very low indeed. And everything that can be said bad about the aerodynamics of a sphere at subsonic velocities goes double or triple once you break the sound barrier. For very small shot, #7.5 – #9, hitting the atmosphere at supersonic velocity is like hitting a brick wall.
What this means is that supersonic shot looses velocity down to the speed of sound almost immediately, within a few feet of the muzzle. I imagine the effects of out-of-roundness are magnified in these first few feet, too. Irregular surfaces produce secondary shock waves and it is the shock waves that soak up so much energy.
The speed of sound under “standard conditions” is 1093 ft/sec. Therefor 2.75 DE loads of 1.125 oz shot at 1150 ft/sec seem to be all that is needed under any conditions.
Do you have any comments?
Do I have comments? Does Vesuvius erupt?
I think that you are pretty much right about extra velocity being mostly wasted. I don’t think that the average hunter afflicted with “magumitis” agrees with us though. Bigger and badder is the generally preference for the once-a-year hunter.
One of the problems with true sub-sonic shotshells is that there isn’t much choice of product. The Winchester Featherlight Low Noise 26 gram load chronographs about 950 fps at 3 feet on my Pro Chrono. The Federal Top Gun Low Recoil Subsonic Ammunition 12 Gauge 2-3/4″ 1-1/8 oz #7-1/2 Shot specs at 900 fps. Every other shotshell that I have ever tested is super-sonic at the muzzle. Every one. I have not seen any sub-sonic reloading data, so I haven’t tried that route.
The sub-sonic ammo is nice for training for skeet, but they will cause some lead readjustment for longer ranges. Also, as a by-product of being sub-sonic, they may not have enough pressure to work the gas guns many of us use. Hence they may be limited only to O/Us. One thing’s for sure- those light sub-sonics are absolutely the softest shooting 12 gauge shotshell I have ever tried, short of a few of my reloads that failed to go off.
You are absolutely right that the faster a pellet starts out, the faster is slows down. I don’ t know if all loads drop to sub-sonic as soon as they leave the muzzle, but most of them sure do. Using Lyman’s figures, a #7-1/2 pellet with a 3 foot super-sonic velocity of 1330 drops to a sub-sonic 930 fps at 20 yards. Start the same pellet 200 feet per second slower at a super-sonic 1135 and at 20 yards it is going 830, only 100 feet per second slower. The slow load has made up 50% of the difference! At 40 yards it is 715 fps to 660 (55 fps difference). At 60 yards it is 580 fps vs 540, only 40 fps difference.
On a pure percentage basis though, it is not nearly so dramatic. The 1330 fps load loses 30% of its velocity at 20 yards, 46% at 40 yards and 56% at 60 yards. The 15% slower 1135 fps loads loses 27%, 42% and 52% respectively. The faster loads scrubs off only 3-4% more if you look at it that way (which I really don’t).
The above example is the main reason why I don’t believe in ultra fast loads of fine shot. I load everything I shoot to 1200 fps and that is it. This permits me to fine tune my leads a bit better (though size of shot does vary the time to target). These relatively light loads also insure that my pellets don’t get deformed by set-back any more than necessary. If you prefer 2-3/4 1-1/8 oz loads at 1150, I have absolutely no argument. I just like to keep things around 1200 fps because when I travel I can always get both 12 bore and sub-gauge ammo in that velocity. I also like the 1200 fps loads as they generate just a touch more gas pressure for reliable operation of the gas gun on cold and wet days. Of course they also generate more recoil and pellet deformation too. If I were limited to 1150 fps, I wouldn’t complain in the slightest, but I don’ t think that there is much difference between 1150 and 1200 in the real world. You would be surprised at what you start to find when you chronograph factory shells.
The eruption is over. You can come out of the shelter now.
The Technoid at <www.ShotgunReport.com>
(Often in error, never in doubt.)