Col. Batguano
75 Cal.
- Joined
- Feb 10, 2011
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Every so often this topic comes up, but it's been a while so I'm starting it again. Simply, the davenport formula seeks to find the optimum / or maximum charge that will be fully consumed within the confines of the barrel. Much more than that, and the powder won't burn until it leaves and makes a nice pretty fireball at the muzzle. The formula is simple; 11.5 grains of powder per cubic inch of bore.
I have a few questions related to it however;
1.) Is that for cap guns or for open touch hole guns? How would it be adjusted between the 2 types? We typically need about 10% more powder in touch hole guns to achieve the same velocities, so that would seem a logical adjustment.
2.) What powder granulation is it made for? I had heard 2Fg, but most people are shooting 3Fg these days in guns with bores smaller than .62. Similar question on adjustment formula.
3.) Does it vary by projectile weight and patch lube / tightness / resistance? If so, what is the adjustment formula?
4.) Would there be a way to verify it using a load and chronograph with your own gun and with your own unique loads*?
*It would seem to me that using low loads (call it 25 gr in a 44" barreled 50 cal) and going up say in 5 grain increments, and knowing that BP burns at a constant rate regardless of pressure rather than logarithmically as pressure increases in smokeless, logic would say that velocity increases would be linear and constant as powder charge is increased, until you hit the optimum number. From that point on, your velocity increases per grain of powder will be a smaller and smaller number, similar to using a bigger and bigger motor on a boat; doubling the horsepower creates a 50% increase in speed.
I have a few questions related to it however;
1.) Is that for cap guns or for open touch hole guns? How would it be adjusted between the 2 types? We typically need about 10% more powder in touch hole guns to achieve the same velocities, so that would seem a logical adjustment.
2.) What powder granulation is it made for? I had heard 2Fg, but most people are shooting 3Fg these days in guns with bores smaller than .62. Similar question on adjustment formula.
3.) Does it vary by projectile weight and patch lube / tightness / resistance? If so, what is the adjustment formula?
4.) Would there be a way to verify it using a load and chronograph with your own gun and with your own unique loads*?
*It would seem to me that using low loads (call it 25 gr in a 44" barreled 50 cal) and going up say in 5 grain increments, and knowing that BP burns at a constant rate regardless of pressure rather than logarithmically as pressure increases in smokeless, logic would say that velocity increases would be linear and constant as powder charge is increased, until you hit the optimum number. From that point on, your velocity increases per grain of powder will be a smaller and smaller number, similar to using a bigger and bigger motor on a boat; doubling the horsepower creates a 50% increase in speed.
