Put a sheet on the ground under the muzzle of your rifle, in front of a shooting bench, and shoot those higher powder charges. If you have UNBURNED powder on the sheet after firing, you are simply pushing powder out the barrel.
Have someone else shoot the gun with a load at 70 grains, and then a load at 100 grains. If you see a much bigger flame or flash outside the muzzle, that is where all that extra powder is burning!( Do this in poor light or at night so you see the flame or flash better.) And, look for the " sparklers" in front of the barrel. If they increase as you increase that powder charge, you are simply burning powder outside the muzzle, and that is not contributing to greater velocity of your ball or bullet.
The Davenport formula tells you when you have reached a point of Diminishing Returns. It does not mean you can't put more powder in the barrel, nor does it mean you may not get more velocity from your ball using more powder.( You are just not getting more bang for your buck!) Generally, you will begin to see that you get LESS velocity for each increment in powder charge the more powder you use over that formula amount.
Those short barreled rifles are handy in the woods, but you do give up some velocity in return. Nothing is free. BP burns progressively, particularly behind a PRB, of that caliber or smaller, because there is not enough MASS in the ball or friction caused by the ball and patch against the bore, to raise the pressure, or chamber temperature behind the PRB to get a quicker burning of the powder.
That is why you get residue of unburned carbon deposits. If you increase the mass, by using OP wads in the barrel, for instance, you will get a better burn, and a more complete burning of the carbon( charcoal), leaving you less gritty residue to clean between shots. An OP wad, or filler, over the powder, is going to provide a much better gas seal in the barrel, than any cloth patch can shooting a soft lead ball.
Gas seals not only prevent the gases from cutting or burning your patch and ball, but they help raise the pressure and temperature in the powder that is burning. We are talking milliseconds, here, but the increases in heat and pressure helps to consume the powder more efficiently.
The Davenport formula applies whether you are shooting a PRB, using an OP wad, or fillers, or shooting conicals, with and without base wads. Its about how the powder burns, and not about what you are pushing with the gases the powder produces. The granules burn from the outside in, and the only way to get more velocity from this compound is to reduce the size of the granule you use.
If you want more velocity, do as many do, and switch from 2Fg to 3Fg powder, but work up your loads carefully, and use a chronograph. Look for spikes in velocities, or drops. Both indicate that something is going on with that load that radically affects where that ball is going to hit, and you probably don't want to use that load.
Swiss powder burns hotter, and faster, because there seems to be a bit more Potassium Nitrate used in the powder, and the granular sizing is based on metrics, and is smaller than what American-made powders are. I suspect that the difference in the formula arises from the use of metric scales of measurement, rather than any real desire to produce a " hotter " Black Powder.
In tests my Brother made using his .40 caliber target rifle, when he used OP wad with both Swiss and Goex powders, the difference in velocity for two similar loads of powder where only about 100 fps apart. Without the OP wad, the difference was closer to 300 fps.
The company claims the powder burns cleaner because they are using only charcoal made from pure Alder( or poplar) lumber, harvested from Eastern Europe. That may be the case. If you mix any pine, for instance, in with your hardwoods before making charcoal, you add pine tars to the mix, and that does not burn efficiently at the temperatures generated in Mler barrels, typically.( Fruit woods would contribute more sap, typically, and that also doesn't burn well).
You don't need a lot of velocity for any PRB to kill deer, at ranges where deer are normally shot when open sights are used. The soft lead ball expands on impact, creating a much larger Primary wound channel, and that is how it kills so efficiently. :hmm: :surrender:
There are lots of members here who kill deer every year with 70 grains of powder and less in their .50s. :hmm: My .50 has a 39 inch barrel, but I shoot " only" 75 grains of 2Fg powder in it out to 100 yds as my hunting load.( So, I guess I basically disagree with your original complaint that 70 grains is NOT ENOUGH powder.)
That 180 grain RB weights a bit more than 4 tenths of an ounce, and its a very heavy projectile to hit game. On broadside shots, the ball completely penetrates most deer. :shocked2:
My first deer was killed at about 40 yards, and that ball broke a rib going in, went through bottom lobes of both lungs, and the aorta on top of the heart, before breaking a second rib on its way out. There are not a lot of modern cartridges that can do much better than that! :thumbsup:
