The HuntingPA.com Outdoor Community banner
1 - 13 of 13 Posts

·
Registered
Joined
·
1,757 Posts
Discussion Starter · #1 ·
grains per inch????

I've read this some where? a certain formula of grains per inch of barrel length will give you an almost total burn of black powder.
Has any one else read this any where?
I don't recall if it was 2.58 grains or what! In my Flintlock and my Wolf,i've loading 65 to 70 grains of 2F,for a good while. This load works very well! I remember trying it after i read that formula and stayed with that amount of powder.
 

·
Registered
Joined
·
3,440 Posts
Re: grains per inch????

cubic in of the barrel for powder
.50 cal Divided by 2 = .25
.25(squarded) X .25 = .0625
.0625 X 3.1416 (Pi) = .19635
.19635 X 11.5 = 2.258 grain per cu in of bore
so it works out for a 32 inch barrel to 72.25 grains
This is what I have seen for powder.
 

·
Registered
Joined
·
185 Posts
Re: grains per inch????

I followed you up to the last calculation. Where does the 11.5 come from? .25 x.25 =.0625
 

·
Registered
Joined
·
3,770 Posts
Re: grains per inch????

As the ID (Inside Diameter) of each caliber is different, I see no way that formula could be valid?
 

·
Registered
Joined
·
3,440 Posts
Re: grains per inch????

Joe the Logger said:
As the ID (Inside Diameter) of each caliber is different, I see no way that formula could be valid?
This is for a .50 cal only and from some old hand written notes,so the note is hard to read.
The best way to to find the right powder load is to start out at 50 gr and work up to find your load that give you the best group.
 

·
Registered
Joined
·
12,402 Posts
Re: grains per inch????

There was a fellow that knew the navy had a formula for calculating the maximum efficiency load for it's artillery. His name was Davenport and he often attended the matcches at Friendship indiana. He tried to adapt the Navy formula to muzzle loader small arms. Because the only powders then commonly avilable were Curtis and Harvey and Goex, which had similar burn rates, he felt there would be a constant that could be computed with bore diameter and length to calculate the most efficient load for round ball match shooting. He consulted with many of the match shooters about their loads, etc and came up with a rough formula of 11.5 grains per cubic inch of bore.,
 

·
Registered
Joined
·
3,770 Posts
Re: grains per inch????

Now it makes sense. Trust me, math was never my strong point, but I knew that much LOL! I am a very simple thinker when it comes to Muzzy shooting. Learn to shoot well, listen to what the oldtimers tell you, and theres not much difference between 70 and 90 grains, MHO.
 

·
Registered
Joined
·
12,402 Posts
Re: grains per inch????

The "Davenport Formula" as some call was a work in progress whhen Mr. Davenport died. It works fairly well for guns between 45 and 54 caliber. For smaller and larger bore guns the formula skews off and doesn't work. It does not take into account, rifle twist, granulation of powder used, whether the powder is hotter than others.

Surprisingly though, it does calculate loads that are within 5 or 10 grains of what most match competitors use. So it can come real close to the ideal load for round ball target shooting. It was still work in progress that can use some tweaking. The Greenhill formula for ideal bullet length and twist for long range shooting worked well for years and when most muzzle velocities exceeded the speed of sound, it was found that the formula needed tweaking.

This is slightly different than the point of diminishing returns for a gun. ie the point at which equal increments in powder no longer yield the same increase in velocity. For instance, for each ten grains of powder in a gun, the velocity will go up by an almost identical increase in feet per second velocity. But when the load gets to the point that not all the powder is consumed within the bore, the velocity increases start dropping off.

I am sure neither Davy Crockett or Daniel Boone ever considered such things. But the folks who designed and built the guns did. After all, it takes an accurate weapon to make a good shot.
 

·
Registered
Joined
·
3,440 Posts
Re: grains per inch????

tobyje said:
I followed you up to the last calculation. Where does the 11.5 come from?
11.5 is grains per cubic inch of the bore
 

·
Registered
Joined
·
1,885 Posts
Re: grains per inch????

So if my math is correct, a .54 caliber 44" barrel would be roughly 107 gr. of powder?
 

·
Registered
Joined
·
12,402 Posts
Re: grains per inch????

.27 x .27 x 3.1417 x 44 x 11.5 = 115.9 grains if my math is correct.

44 inches is quite a long 54 barrel. And this is where things start to skew off.

for instance the formula for a 54 cal 30 inch barrel would be
.27 x .27 x 3.1417 x 30 x 11.5 = 79 grains. Darn close to what most target shooters use in such a rifle.

On the other hand according to Lyman's Black Powder handbook, the point of diminishing returns for loads is 120 grains.

Lets say you just got a new Lyman GPR in 50 cal with a 32 inch barrel

.25 x .25 x 3.1417 x 32 x 11.5 = 72.25 grains

or an early TC hawken in 45 cal, 28 inch barrel

.225 x .225 x 3.1417 x 28 x 11.5 = 51.2 grains

according to Lyman's book, the point of diminishing returns for loads for this gun would be between 80 and 90 grains.
 

·
Registered
Joined
·
1,885 Posts
Re: grains per inch????

So 115gr would be an ideal upper limit? Or is that number skewed because of the length?
 

·
Registered
Joined
·
12,402 Posts
Re: grains per inch????

It is skewed somewhat. Well lets say you had a 66 inch barrel, would 180 grains seem reasonable?
I would not be shooting that as a match load.
For most normal production and target guns the formula works for a close approximate match load.

A 44 inch barrel is not something I would want to be raising and holding 100 times in an afternoon of match shooting. Most match guns are also built with the idea of avoiding shooter fatigue caused by lifting, holding and aiming heavy barrels. 44 inches has got to put a lot of work on the left hand and arm.
 
1 - 13 of 13 Posts
Top