loads and Accuracy

[jaybrown]

Hey guys. I've been reading the forums quite a bit and it seems that each gun has its likes and dislikes with each reload. I hear people talk about increasing their loads changing primers/bullets and finding a reload that has the best accuracy. My direct question is; Why would changing my powder from 4.0grains to 4.3grains, for instance, improve my accuracy? I know this is true from what I've read on the forums but I'm interested in the theory behind it. Thanks

 

[steve4102]

Barrel Harmonics. Think of it this way, when a bullet is fired the barrel begins to move and oscillate, lets assume that the movement of the barrel is in the shape of a figure 8. The point at which the barrel movement is the least would be when it is changing directions on the figure 8. Getting the bullet to exit the barrel at these points will have the best accuracy due to less barrel movement. This may help explain it better than I.
http://www.browning.com/faq/detail.asp?ID=108

 

[Smokey Joe]

Changing loads

When you change the amount of powder behind a bullet (assuming all else stays the same) you change the pressure generated when that cartridge is fired. This will change the velocity of the bullet, as well as changing the barrel's vibration.

Now, I'm no ballistician, but on a practical level, it can be demonstrated that each particular gun "likes" a particular bullet velocity. That velocity works best with the barrel's vibration and harmonics, with that bullet.

Change the powder charge, or anything else in the reload recipie, and you change the bullet speed. The gun may or may not shoot more accurately as a result.

You mention using 4.0 or 4.3 grains of powder, which suggests to me that you are reloading a pistol round. With pistol accuracy, so much depends on shooter technique and skill that the change in accuracy may not be apparent. With an accurate rifle and a skilled shooter, however, changing, say, a 50.0 grain powder charge to 50.3 grains would make a noticeable difference.

 

[jaybrown]

Thank you Smokey joe and Steve. That shedded some light on the subject. I am shooting for my 40S&W. I can see how bullet velocity would be more of a factor in a rifle than a pistol with a rifle having a considerable amount of barrel length compaired to the pistol. There are alot of dynamics of a shot that I never considered before. So much to learn

 

[TN Shooter]

The information about barrel harmonics mentioned above is certainly correct. I would like to add another factor to consider: Upon detonation, the pressure of the powder behind the bullet causes the bullet to shorten in overall length and to increase in width (on a small scale, of course). This increase in width helps the bullet to engage the rifling. Thus, the amount of powder will affect the ability of the bullet to gain the proper rotation for good accuracy.