In a one ounce load, the difference in the weight of the powder charge between those two loads is a tad under two percent, and you can feel the difference? I don't think it's the weight, others' opinions may vary.
Maybe what Eightbore meant was that the difference in total payload, due to a 10-grain increase in the powder, is 2%....because it is.
Assuming 438 grains of shot and 15 grains of powder, an additional 10 grains of powder increases the total mass by 2.2%.
I, too, questioned how, all else remaining constant, 25 grains of powder could make recoil more noticeable than 15 grains of powder. Expecting to find an increase in free recoil energy of only about 2%, I plugged the numbers into 2 online recoil calculators and got the same result....a 14% increase! how could this be? adding 2% more mass gave a 14% increase?
So then I kept the powder charge constant at 15 grains and upped the shot by 10 grains to arrive at the same total 2% mass increase....and the calclators showed a 4.2% increase in FRE. That's more like it. But why would 10 grains of powder count more than triple the 10 grains of lead?
Turns out the answer has to due with the ejecting powder gases that some doubt are real.
If you dig into the formulas used by people who programmed the recoil calculators, you'll find that powder charge is not trivial. I guess sometimes it really
is rocket science.
Three elements enter in producing recoil. The first is the reaction to the acceleration of the bullet as it moves down the barrel until it leaves the barrel at it’s maximum velocity = muzzle velocity. The second element is the reaction to the acceleration of the expanding gas generated by the burning powder. The third element is the reaction of muzzle blast when the bullet leaves the barrel and the escaping gas gives a reactive push to the muzzle. As pointed out earlier, anybody who's ever used a muzzle brake knows this is real and significant....a .300 Win Mag is made to feel like a .243 with no loss of bullet velocity. As a general rule of thumb, the escaping gas velocity is about one and a half times the bullet velocity. A value of 4,000 is sufficiently accurate for practical purposes with small arms having muzzle velocities between 1,000 and 4,200 fps.
In general terms, this means that the Momentum of the gun (recoil) = momentum of the shot + momentum of the powder gases.
For a 1 ounce load at 1200 fps, the shot contributes 438 x 1200 and the powder 15 x 4,000 to the total FRE. You can see that adding 10 grains of shot isn't nearly as significant as adding 10 grains more powder, due to the big difference in velocity.
To test my understanding, I used a muzzle velocity of 4,000 fps so the projectile and gases had the same velocity. When I did that, increasing the shot or the powder by the same amount gave the same recoil increase.
Welcome to academia! A few of us shoot from the hip and a few of us are duds, but no live ammo was fired in the course of this discussion.
