doublegunshop.com - home Forums General Discussion DoubleGun BBS @ doublegunshop.com 3/4oz 12ga shells

Re velocity, forward allowance, flight time, etc: It is indeed true that faster loads slow down quicker than slower loads. But as far as difference in forward allowance goes, it's still going to be greater at longer range than at closer range--for the simple reason that while the velocity advantage of the faster load over the slower load is reduced, the faster load will always retain some velocity advantage.

For example, let's take two 12ga, 1 1/8 oz lead target loads. MV of the fast one is 1400 fps; the slow one, 1100 fps. At 20 yards, fast load velocity is 951 fps; slow load, 790 fps. Flight time to 20 yards is .0511 seconds for the fast load; .0630 for the slow load. At 40 yards, velocities are 679 fps vs 574 fps. Flight time, fast vs slow: .1265 seconds vs .1529 seconds. (Source: John Taylor's "Shotshells and Ballistics".) Which means, even though the difference in velocity between fast and slow loads has been reduced, you need more forward allowance to compensate at 40 yards than you do at 20 yards.

The area in which the slow load does a much better job of "catching up" to the fast load is not in flight time, nor is it in forward allowance (the gap actually widening in both cases) but rather in retained energy (striking/killing power)--because that's based strictly on retained velocity, and that's the area in which slower loads don't give up all that much to faster ones.

That's a lot of words to say drag increases exponentially with increase velocity.

While I am not a balistician I think that the major reason the light shot losds are loaded to a high veloity has not been mentioned. This is to give a high enough pressure to ensure adequate burning of the powder. "Dirty" burning is not really a great problem "Unless" it is an indication of burning at a lower pressure than the powder was designed for. Stuck wads left in a bore are a great problem.
It is my understanding that when the 2" 12 ga was developed in England the original intent had been to load a 3/4oz shot load. No suitable powder of that age was found for the 3/4oz charge so a 7/8oz load was settled upon.
"IF" you are laoding a powder which is ordinarily clean burning & upon lowering the ballistics it starts burning "Dirty" be extremely cautious with those loads & look down the bore after every shot.

Gil: I am sorry to have abandoned the computer for a few days and not replied to your question. The load I use for doves is the standard Killer Bee data put out by BPI. It utilizes a small charge of Tightwad powder, low pressure be assured. One can use as little as 15 gr. and have a really low recoil round. (Great for women and beginners) The KB's are so low as it is, I think I could shoot all day in Argentina! Both will cycle an auto. Seems to burn clean. Now--for the reasoning...
Bob Brister had BPI originate the load because of his detached retina. If the recoil is low enough for that, it is LOW indeed. But the reason I like them is that they allow me to "DIAL IN" my instinctive shooting. Doves at 40+ yards are deceptively hard to hit. When my brain says shoot at 25-35 yds, no problem. The same unthinking, "concentrate on the bird" effort out yonder, and I am left wondering why I missed. The faster speed has corrected it for me. You can talk about how many thousandths of a second is saved--HAVE YOU EVER COMPUTED HOW FAR THE TARGET MOVES IN THAT GIVEN BIT OF TIME? Just enough for the dove to survive! There is only a fraction of a second required for the antelope to elude the cheetah. The cheetah will not be consoled by ballistic excuses for his miss if he is walking home hungry. I think you could vary the speed of the 3/4 oz. loads until you come up with the perfect solution to the diff. between what your brain says is trigger time and what WORKS. I am into what works, and THIS DOES. TRY IT! It requires the right wad (BPI suggests theirs, but whatever will fit the shot) the low charge of Tightwad, and your choice of shot size and quality. Nothing to it! And I am not into high pressure loads, so even if the recipes on the bottle of Longshot powder describe 1 1/8 loads going 1560 fps, I am NOT on board with the pressure or the sharp recoil. As far as I am concerned the increased velocity is for 3/4 oz and not more. And I have made enough 60 yd. shots with tight mod. choke (shots run long where I hunt) to really open some eyes...Steve

Say we have a 40 mph (60 fps) 90 degree crossing target a 20 yds. Target movement for the high vel load is 0.0511 sec X 60 fps = 3.07 ft and the low vel load is 0.0630 X 60 = 3.78. The low vel needs 0.71 ft = 8.5 inches more forward allowance (23% more) for the same pattern placement. At 40 yards: 0.1265 X 60 = 7.59' and 0.1529 X 60 = 9.174, so 9.174' - 7.59' = 1.584' = 19" additional forward allowance (21% more).

DDA

Maybe that is why we often do better with O/U's. We use faster loads. I may use a low pressure load traveling at near 1100 fps in my old SxS's whereas for an O/U I might use a shell going at 1250 fps. At 40 yards the diffence in speed would account for an 8" or so diffence (not doing the calculation). That is not a small distance. Since most shooters miss behind...........You figure the rest out.

8" for 150 fps--and the 1520 fps Killer Bees begin to show why those of us who shoot behind are really caught up to speed with those doves. If the calculations hold up through the speed range, a 1520 fps shot charge is almost 24" ahead of the 1100 fps load. THAT is not insignificant for sure!

Steve,
I didn't and won't check your math, but I beleive you are within the scatter factor for TLAR (that looks about right).

Steve, it looks like you mixed Larry's downrange velocity with muzzle velocity for the Killerbeez. My SWAG/LAR would be more like 11 inches (Larry's LV @ 1100 fps vs HV@1400 fps vs KB@1520 fps). The HV is 300 fps faster than the LV and the KB is 420 faster than the LV.

DDA

Oops...I believe you may be right about downrange vs. muzzle velocity. Apples and oranges...Still, I'll take a 25% improvement on doves even if I don't understand it mathematically! The "Old Curmudgeon over at BPI has come up with low recoil, low pressure 3/4 oz. loads for the 16 ga. My nephew had his wife try them and she is hooked.