You can shoot at any metal can, but NOT ALUMINUM, for your testing. Coffee, vegetable or fruit cans, juice cans-- anything made of steel and coated in tin or some other flashing will give similar results. Cat food and dog food cans work, too.
Because your shotgun is an " odd " gauge, there just is not going to be any data for that gauge. There are too many variables, and information you have not shared with us, for any of us to do anything more than make a guess.
I gave you, earlier, my estimate on velocity ranges and powder and shot loads to use.
I show a 2 1/2 dram(69 grain) powder charge of FFg Goex BP with 1 oz. of shot to give MV of 1014 fps. according to the Hodgdon Reloading manual. That is considered a MEDIUM load in a 16 gauge, and a HEAVY load in a 20 gauge, which is smaller in diameter. It represents a fair AVERAGE load for your gauge, which falls between the 16 and 20 gauge shotguns. NO?
Now, in a classic work by Greener, published in the 1870s or 80s, titled," The Gun and its Development", he lists the following velocities for the same load- 2 1/2 Drams and 1 oz. of shot as follows:
MV( 5 yds) 1039 ( close enough to the Hodgdon data for our purposes.)
5 yd; = 1039 fps.
10 yd: = 1022 fps.
15 yd: = 1001 fps.
20 yd: = 979 fps.
25 yd: = 951 fps.
30 yd: = 929 fps.
35 yd: = 904 fps.
You can see, by plotting these numbers on a graph, that you are losing about 22 fps every 5 yards. Use 25 fps. as an average, and to simplify calculations, ie, every 20 yards, you lose 100 fps.
Now, pellet energy is something else. The only place I have seen pellet energy figures is in the tables in the Lyman Shotshell Reloading Manual. You can extrapolate drop in pellet energy from the tables for different size shot pellets, by comparing the fastest, and slowest load show for each size pellet.
#6 shot, which is what you are using, has data for a MV of 1330 fps. as the fastest, and 1135 fps. as the slowests.
Here is the data for the high and low:
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Highest load:
MV. /20yds /40 yds
1330 fps /970 fps /760 fps
Pellet energy in ft. lbs.
Muzzle: /20 yds. /40 yds
7.62 /4.05 /2.52
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Lowest load:
MV. /20 yds /40 yds
1135 /860 fps /695 fps
Pellet Energy in Ft. lbs.
Muzzle: /20 yds /40 yds
5.55 / 3.19 / 2.08
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Looking at the percentage of energy lost at 20 and 40 yards over what was at the muzzle, its clear that you are going to see a pellet energy loss at 20 yards of between 40 and 50% of the energy at the muzzle. At 40 yards, you lose 60% of the energy that you had at the muzzle. These percentages do get worse for small sized shot pellets, and better for larger sized shot pellets, simply because the larger diameter of a #2, or #4 shot pellet gives the pellet a greater Ballistic's Coefficient.
If you subtract 25% of the velocity of a load beginning at 1014 fps MV, you get 760 fps for your estimated 20 yard velocity.
Pellet energy for a #6 pellet traveling at 760 fps. is show on the table as 2.49 ft. lbs. At 40 yards, the pellet is traveling 628 fps, and has a retained Pellet energy of only 1.68 ft lbs.
Extrapolating data a bit, at 30 yards, your pellet energy is about 2.08 ft. lbs.
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By comparison, A #5 pellet, at 760 fps has 3.30 ft lbs. of energy; at 628 fps., it retains 2.23 ft lbs. of energy.
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Although birds have been killed with just one pellet hitting the brain, you usually want a margin of error of 1.5 ft. lbs. per pound of bird. The average Pheasant Rooster rarely goes 4 lbs, and 6 pellet hits will insure a clean kill most of the time. Again, I have seen pheasants taken down with just one pellet hitting them, and at extremely long yardage.
A turkey is obviously considerably heavier than a pheasant. The difference is that with Pheasants, you are shooting at a moving target, and hitting the entire body, hoping to drive a pellet into vital organs, or to shock the bird to death with multiple hits. With The turkey, you are shooting at a standing target MOST OF THE TIME, and the feathers on the bird are darn near armour plating, making it difficult to put any pellets through them to get into the vital organs. The Head and Neck of the turkey therefore are the TARGET.
If you can put 12 pellets on the bird's neck and head at a known distance, I think you can be assured you will kill the bird. I have seen large 25 lb. Wild turkey killed with as few as 6 hits in the neck and head, where #6 shot was used, but the yardage was only 20 yards.
* At that distance, the pellet has 2.5 ft. lbs. of energy, so the neck and head were hit with 18 ft. lbs. of energy. All it took was one of those pellets to reach the spine, or brain, and death was instantaneous. The hunter was surprised that so few pellets hit the head and neck, BTW. He had practiced his shooting at turkey targets for weeks before the hunt, and expected more than 15 hits or more, on the head and neck at that distance based on his targets.
Roundball's Advice to use life-size paper Turkey targets is excellent, and realistic. Most guns can be made to shoot a load that can put a pattern out dense enough to put pellets on the small area that is the neck and head, at some yardage. But, many shooters cannot consistently point their guns the same way, shot for shot, and if the pattern is not centered, as it probably is at the range, you can miss the turkey, or simply cripple it, only to see it fly or run off to die somewhere you can find it.
Practice your shooting with your turkey loads. A copy machine can be used to print out dozens of the targets to use at the range, so you can shoot from a variety of positions, and distances, to learn what YOU have to do to get the shot pattern on target. I am a huge fan of hunters using guns with rear sights for this kind of hunting, simply because it eliminates much of the human error that can only lead to crippled and lost birds. If you can go to a sporting clays range, shoot some shots at the various distances, at incoming and crossing targets to get a feel for how the gun moves, the lead needed in case the bird is moving, or flying , etc. If nothing else, shooting at clays gives you more confidence on that standing target.
