Posted: 10/12/2008 5:39:26 AM EDT
| So first off I would like to say that I know very little about making ammo and powder types and what not. I met this guy the other day who was telling me that he makes his own ammo and he was trying to dial in the his formula for making ammo for a particular gun that he has. While he was explaining this he mentioned something about trying to find the right harmonic for his gun barrel. Is it true that you can actually do this, it seems logical that it would have a certain harmonic to it but does it really make that much of a difference? If it is true could somebody please explain? |
Yes, he is right. Barrels whip like a sine-wave. If you load to a velocity that the bullet leaves the barrel at the dwell of the curve, you will get a tight group. Unfortunately each barrel is different. |
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Yes. This is why small differences in MV can lead to large differences in point of impact. If the MV is absolutely consistent, then the barrel's position in flex at the moment the bullet leaves the barrel will be very consistent. A small variation in muzzle velocity will change the phasing of the barrel vs. the time the bullet exits, causing a different point of aim and different point of impact. If you're really serious about shooting for score, you'll work up test loads that are maybe a 10th of a grain apart, 10 rounds each, shoot each of them from the bench, and observe not your point of impact, but your group size. I guarantee that some groups will be tighter than others. They are the ones that are optimized for your barrel and its harmonic behavior. But you need to work up these test loads with all the consistency you can possibly bring to bear on the problem. Use a sensitive scale and pre-weigh every component. Match case weights and bullet weights as well as powder charge weights. Once you've established your BEST accuracy load, set that as your reference point and that's your nominal load. Your production ammo may not be quite as precise if you don't bother to weigh and match the components, but it'll average out very well. CJ |
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Optimal barrel time theory HARMONICS This will help to explain in the technical nature, the above posters have given a partial overview to some of the factors affecting accuracy during the internal ballistics portion of the bullets travel. |
Also, small differences in the powder burn rate (acceleration of the bullet) at the same muzzle velocity can lead to large differences in point of impact. Not only differences in the point of impact but differences in the size of the groups. The barrel does move like a garden hose being slung up and down. If the bullets all leave the barrel at the same point on the curve the groups will likely be small. The easiest places to achieve that are at the very top and very bottom because that is where the muzzle is moving the slowest and in fact it stops for a very short period of time at each end. Near the middle of that curve the muzzle is moving fastest so small differences in the velocity of the bullet make the most difference. |