Maximum amount of powder burn

[drago]

Is there a formula to determine this. I am looking for 2FF in a .54 32 inch barrel. I need to get to the range to work out loads but wanted to know where the wasting powder starts. Wanting to get flatter trajectories to buck the wind.

[jamesthomas]

 The only way is to get out there and shoot it, you will find the sweet spot way before you reach the max. 

[galamb]

There is a somewhat controversial formula out there (sometimes called the Davenport formula) that is supposed to calculate the most efficient load for a given barrel - after which you get into "diminishing returns" (percentage of powder burned significantly outweighs the increase in speed).

Anyhow, the formula states that for each cubic inch of barrel you have it can effectively/efficiently burn 11.5 grains of powder (not my formula and can't explain where the number came from).

So in a 54 cal you need to calculate the cubic inches of barrel which is done as follows.

Radius of the bore x Radius of the bore x pi x 11.5 x length of the barrel in inches OR

.27 (radius) x .27 (radius) = .0729 x 3.1416 (pi - rounded) = .2290 x 11.5 (grains) = 2.63 (grains per inch of barrel) x 32 (inches of your barrel) = 84.3 (round up to 85 grains).

So this doesn't mean you won't get more speed above 85 grains of powder, simply that the gain (in percent) will be minimal compared to the increased gain in powder usage.

Take it for what it's worth.

I compared the results to what I shoot and it works for me.

[JPK]

I don't know any math for your question but I chorographed my 32" 54 and found that velocity flattened out at 110 gr. of 2f GOEX and groups were still good as I can hold. I got 1818 fps and 19.5 sd using .535 ball.

[drago]

Was it much faster than 85 grains? I'm not looking for magnum loads just the most useful amount. Unless a wholly mammoth strolls across the range, then I'll just fill-er up.

[okawbow]

My 30" barreled flintlock handles 110 grains Goex and seems to burn it all. It shoots fairly flat out to 130 yards with that load. 100 grains is not as flat or as accurate.

[galamb]

I am "somewhat" of a mathematical shooter. If you want to go that route you have to "know" what YOUR variables are.

My primary interest is in getting my rifle to shoot to my sighting range (50 yards) with a trajectory that neither rises or falls more than 1" from the point of aim - so I want a point blank range +/- 1" to 50 yards.

If I want to stretch that out to 100 yards, with the same restrictions/requirements then I will have to use substantially more powder, well past the point of diminishing returns to achieve that.

So the question becomes - how far do you want to reach out without having to hold high or low if the target presents itself "closer".

Until you figure that out then trying to "mathematically" calculate a load is impossible.

My 45 cal, which I had well chronographed had a mathematically "efficient" load of 80 grains.

With 80 grains I got 1700 fps (10 feet from the muzzle). If I upped it to 100 grains (25% more powder) the speed increased to 1860 fps (9% more speed).

With 80 grains and a 50 yard zero I retain a 1" PBR out to 75 yards. (but I also get a +/- 1" PBR out to 75 with 70 grains, so no need to waste extra powder)

With 100 grains I can go with a 75 yard zero and my 1" PBR stretches out to 100 yards.

If I "need" 100 yards of range, then I need to shoot 100 grains otherwise I save my powder.

[WadePatton]

The volumetric efficiency calculations just give an efficiency point.  Efficiency means nothing without accuracy and acceptable trajectories.  And I'm leaning toward accuracy first, learning the trajectories from that most accurate load. 

It's good information to have but there is no substitute for range time and powder burnt.

also there's an example ^^^ (what he said).

[little joe]

Don Davis used to say ball weight divided by 7 multipled by 3 as a very good load. He usually gave very good agvice.

[smylee grouch]

How tight is your load -patch/ball combo in your bore? A tighter combo might effect burn characteristics.

[Daryl]

Use the most accurate load with a tight combination - one that will shoot cleanly enough not to need wiping while shooting.  Wipe if you want, but if the load is tight enough not to need it and the patches are literally good enough to use over again, then you will realize higher speed per load, flatter shooting & continually better accuracy as the charges go up to about 110 to 120gr. of 2F powder. 

[Jerry V Lape]

Mr. Drago wants to "buck the wind" with a flatter trajectory.  The truth is he  isn't going to get a enough of a velocity increase to make a significant time of flight reduction to make a difference which will be noticeable within the average shooters aiming errors.  Better to pursue the most accurate load then use your shooting skills to apply a little Kentucky windage to adjust for crosswinds.  Also a few extra fps at the muzzle shooting a round ball is quickly reduced early in the flight to insignificance anyway. 

[Mad Monk]

The idea that one may calculate the proper amount of powder to use in a particular gun, shooting black powder, do not take into account the actual differences in how different powders burn in the bore.  There is a big difference between what works best if you compare a very fast and hot burning power like the Swiss powder versus a rifle burn rate powder such as GOEX.

Shooters think of powder burn rates only in terms of grain sizing when the real burn rate is a point of powder combustion reactions determined by the chemistry of the powder.

Old writings talked about the "expansive force" of a powder.  That involves how much total volume of gases produced, at a certain rate and at a certain temperature.
For instance.  Maximum gas temperatures.  A musket burn rate powder will give about 1800 degrees gas temperature.  A rifle powder around 1900 degrees and a fast burning sporting powder about 2,000 degrees.

In the gun.  A point is reached in pressure development where the projectile can no longer respond, or accelerate, to an increase in this expansive force.  That is in effect the point of diminishing returns.  That may be looked at using chronograph data with uniform incremental increases in the powder charge.  One may also look at this in terms of how tight the resulting groups are.  Generally.  As you go above this point of diminishing returns the groups will open up.


Mad Monk

[rtadams]

8-31-13


To clarify galamb's  "length of the barrel in inches" as related to length of rifle barrel bore length: the actual usable bore length is the total barrel length minus the length of the breech plug engagement at the breech of the barrel. Example  --- Total barrel length (32") minus breech plug length engagement at the breech (.5") Equals --- (31.5") actual barrel bore length.
The rifling groove volume should also be included for actual total rifle bore cubic inches but is a complicated calculation and the additional cubic inches is very very small. I usually do not include the rifling groove cubic inches in my Internal Ballistic Software Program calculations for Black Powder.
Mathematical Internal Ballistics calculations to obtain muzzle velocity are so complicated by so many variables that any mathematical method used, can only be at best a starting point for the amount of Black Powder to use. A good starting point if so inclined would be to use the 11.5 grains of Black Powder for each cubic inch of barrel bore length and supplement using Chronographic muzzle velocity measurements to determine the most efficient powder charge as related to muzzle velocity for a specific shooting distance. I am very familiar with the "Davenport" calculation and use it for starters in developing Muzzle Velocity Mathematically.
Also, for those so inclined may apply a proven Round Ball External Ballistic Software program to analyze the muzzle velocity for the selected distance to determine the round ball's drop due to Acceleration due to Gravity, windage drift of round ball due to wind velocity/direction and round ball's ft lbs of energy at target  etc.  
As many responses have indicated and I quote WadePatton, "It's good information to have but there is no substitute for range time and powder burnt" as related to the amount of Black Powder to use when developing and obtaining a accurate load.

Best Regards,

Robert

[Standing Bear]

Don Davis used to say ball weight divided by 7 multipled by 3 as a very good load. He usually gave very good agvice.

No variance for barrel length?

[WadePatton]

Don Davis used to say ball weight divided by 7 multipled by 3 as a very good load. He usually gave very good agvice.

No variance for barrel length?

Maybe you're still missing the big picture eh?

which is, that no matter how precise the formula or how smart the engineer, that there are simply too many variables contributing to actual observed accuracy/consistency/velocity for the TRUTH with regard to any particular ONE gun to be exposed by any such calculations. 

It's all just jumping off points to be reconciled/refined by range time. 

[galamb]

Agree. When I finish a gun I use the Davenport formula to determine my starting point.

From there I go up and down (and usually down first) in 5 grain increments until I get the group (sub 2") and point blank range (of 1" or less) that I am looking for.

It's simply a starting point no different than covering the ball in your palm with powder or starting at grains equal to the caliber.

[PPatch]

Mr. Drago wants to "buck the wind" with a flatter trajectory.  The truth is he  isn't going to get a enough of a velocity increase to make a significant time of flight reduction to make a difference which will be noticeable within the average shooters aiming errors.  Better to pursue the most accurate load then use your shooting skills to apply a little Kentucky windage to adjust for crosswinds.  Also a few extra fps at the muzzle shooting a round ball is quickly reduced early in the flight to insignificance anyway. 

True. The instant the ball leaves the barrel it is "in" the wind and point of impact is affected. Just as an aircraft when it lifts off is "in" the wind and travels effected by the prevailing wind. A pilot compensates for wind drift to achieve his true course across the earth and a shooter must apply a windage calculation in order to hit what they aim at, there is no getting around it. A faster ball only means it is in the wind a relatively shorter period of time and thus effected somewhat less but you'll still have to hold into the wind.

dp

I see Point Blank has entered the discussion, I was wondering when it would because it is an important consideration also.

[Daryl]

I would argue that using any powder charge that was not the rifle's "accuracy load" was wasting powder.

[galamb]

Disagree.

The absolute "most accurate" load in say my 45 cal might be 80 grains.

BUT, I only NEED accuracy of sub-2" at 50 yards and can achieve that easily with 65 grains.

Why would I burn the extra 15 grains with each shot to achieve a level of accuracy that I do not need?

[bob in the woods]

When I don't need the accuracy that my rifle is capable of,  I use my smoothbore 
It's my most often carried hunting gun     

[WadePatton]

Disagree.

The absolute "most accurate" load in say my 45 cal might be 80 grains.

BUT, I only NEED accuracy of sub-2" at 50 yards and can achieve that easily with 65 grains.

Why would I burn the extra 15 grains with each shot to achieve a level of accuracy that I do not need?

If you are shooting over known distances with every shot,  and landing everything in the X, cutting all the strings then sure I agree.  Save them powder.

But I hunt and never know at what distance game may present itself, and on the range i want X, not just black.  So I'll burn some more powder in order to make bester connections.  if i hold my mouth right and the creek don't rise.

I want every last thing i am in control of to contribute to putting the ball into the kill zone of game or into the X of the target.

 If the ball does not connect the _entire_ powder charge was wasted.

[Daryl]

Disagree.

The absolute "most accurate" load in say my 45 cal might be 80 grains.

BUT, I only NEED accuracy of sub-2" at 50 yards and can achieve that easily with 65 grains.

Why would I burn the extra 15 grains with each shot to achieve a level of accuracy that I do not need?

 galamb - if you reduce your accuracy requirements even further, you can save even more powder.

[Hungry Horse]

Just spread an old bed sheet in front of your firing position, or wait til it snows, and slowly increase the charge, until you start to see unburned powder grains on the sheet/snow.
 Someone asking how much powder they can safely shoot in a gun, is like when someone wants to drive my old muscle car, and the first question out of their mouths is how fast will it go. Big red flag in my book.
 Most people that shoot a fat load in a big caliber muzzleloader offhand soon find they can't hold steady enough to shoot serious targets, because they are anticipating that swift kick in the puss.

                 Hungry Horse

[Dphariss]

There is no formula that will work across a wide range of calibers.
1/2 ball weight good for 45-50 and close for a 54. In a 67 caliber you would be shooting about 220 grains of powder and recoil would be really nasty. In a 75 caliber 1/2 ball weight gets completely ridiculous.
For something like a 32 1/2 ball weight is too little and may need 70% of ball weight.
Formulas of how much powder the bore will burn are silly and will at best provide the point of diminishing returns.
So where to start? 30 grains for 32-36 cal, 40 cal maybe 35-40, 45-54 about 1/2 ball weight. 58? 100 to 120. Over 62 use 30% of ball weight for 67-69. Over that? Got to Greeners the Gun and Its Development for service loads. From what John Taylor related in "Pondoro" a 10 ga smoothbore will kill African Elephant with lung shots using 167 gr of powder and a hardened ball.  Velocity also goes down as the ball get bigger. 1600 will give as flat a trajectory as I need with a .662 ball. 1700-1900 is better for the 45-55 cals.  Shoots nice and flat for hunting.

So pick a caliber range, use a ball no more than .005 under bore, patch thickness .015-.020. Lubes are a world of their own. The high friction lubes shoot best usually, slicker oil-tallow types for hunting.  Use a SOLID rest and wiping every shot so the bore is uniform shoot 5 shot groups at 50 yards going up 5 gr at a time till you find what modern shooters call a "node". With no wind if its a good barrel it will shoot a very small group at 50 1/2-3/4". Then you can start working on where is the best place to rest the forend/barrel if you shoot rest matches. Where its rested can effect the group as can what its rested on and all the other hair pulling minutia that is needed for best group size.

Dan