Chrony's - What true purpose do they serve?

[John Y Cannuck]

To be really safe, and know what you are doing, the reloader should use as many of the available tools, and techniques as possible.
I use a chronograph whenever I work up a new load.
Books are different sometimes, and the chronograph can help you sort out who is right, for your load.

one word of caution
A chronograph can turn you into a velocity hound. Don't let it happen, it is big trouble. Work on accuracy don't push the limits for speed.

 

[Boomer]

I thought I read somewhere that there's a correlation to barrel length, rate of twist, BC and FPS that determined best accuracy, but I can't find that information anymore.. or even if it was just someone proclaiming to be an expert. It's alot of variables, but hopefully it means building a accurate load more quickly when switching powders and bullet type/weights.

The most accurate part of the rifle barrel is the point at which it is the tightest. If this dimension coincides with the muzzle of your rifle it is a happy situation. I have heard all sorts of things about rate of twist effecting the accuracy of this bullet or that, but here's what I've observed. Rifles with slow rates of twists do not stabilize long bullets particularly well. This situation can result from loading heavy for caliber bullets, mono-metal bullets, or heavy for caliber mono-metal bullets. I've had 3 rifles with very fast twists. In each case they shot all weights of bullets very well. I've had a number of rifles fail to stabilize very long bullets. As a result I like fast twist barrels.

The search for accuracy begins with attention to detail. The closer you can make a cartridge mirror the one before it, the greater the accuracy potential. Barrel length effects two factors. First, longer barrels tend to allow bullets to reach a higher velocity, although perhaps not as fast as one may at first think. Secondly, the longer the barrel, the greater the tendency there is for that barrel to whip. Short barrels tend to be stiffer, particularly barrels of light contour. If your loads are clones of each other and the velocity is identical from one round to another, barrel whipping would present no effect to accuracy because the barrel would be in exactly the same position each time the bullet left the muzzle. In the real world however, we seldom see single digit variations in velocity, therefore a whippy barrel might not be in exactly the same position every time the bullet leaves the muzzle, and accuracy suffers as a result.

The best accuracy is often obtained when the cartridge case is full or nearly full of powder. I hear 95% is optimum, and I won't argue the fact. Extruded powder takes up more room than ball powder, and we require a greater volume of slow burning powder to get the velocity as we might observe with a small volume of fast burning powder. The key is to determine which powder will give you good load density, fill the capacity of the cartridge, and produce an optimum velocity with a given bullet weight.

Advertised BC have more to do as a marketing tool than as a true indication of the bullet's trajectory. BC also changes as the down range velocity drops off. For that reason you are better off to work out drop tables specific to your rifle and load.

 

[Gatehouse]

As I explained, you increase the powder charge a full grain per round for rifle cartridges. The plateau you observed by increasing a quarter of a grain could of been caused by the difference in case capacity of each cartridge. Done properly, using a velocity plateau as a means of determining the maximum load is safe and repeatable. If it wasn't I wouldn't use it, and I've used it in both handgun and and a broad range of rifle cartridges for quite some time.

That's what I do, and while playing with a new load, I take one example of each and shoot them at the same target, and note where they hit. I do this until I get to the veloiocity I want, and then fine tune. This sure cuts down on load development time.

 

[GrBear]

That's what I do, and while playing with a new load, I take one example of each and shoot them at the same target, and note where they hit. I do this until I get to the veloiocity I want, and then fine tune. This sure cuts down on load development time.

Curiosity has me ask.. once you've achieved the velocity your looking for.. how does that relate to accuracy? or I guess another way to phrase that.. how do you adjust for accuracy then once you've determined your target velocity.

 

[blargon]

Curiosity has me ask.. once you've achieved the velocity your looking for.. how does that relate to accuracy? or I guess another way to phrase that.. how do you adjust for accuracy then once you've determined your target velocity.

Bullet seating depth, or adjusting your charge .1 at a time up or down.

 

[Boomer]

I come at the accuracy problem in one of two different ways; one way if I am loading rounds for a hunting rifle, another when I load for a target rifle. The first step in either case is to determine the maximum working load as we have previously discussed. When I load for a target rifle I seat the bullet seated firmly in lands. Normally this produces the best accuracy as it uniforms the bullet pull weight, but should I want to adjust the seating depth, any adjustment will reduce pressure rather than increase it.

If the load is for a hunting rifle, I usually choose a bullet with a crimping groove, and crimp the bullet in place. This takes care of uniforming the bullet pull weight, so if accuracy needs fine tuning, the only adjustment necessary is the powder charge. Again, any adjustment to the powder charge reduces pressure, as it moves below the maximum load, it does not increase pressure. I am often satisfied with the accuracy I get from the maximum working load for use in a hunting rifle. While accuracy is important, terminal performance is the key to success. MOA accuracy is twice the accuracy needed for a big game rifle.

Target rifles can take a little bit more tuning, although I work on the premise that an accurate rifle will fire good ammunition accurately, so I don't over do the load development. There is other shooting I want to do. My best group with this system is very small, but since I can't do that on demand I don't dwell on it. The load development goes like this:

I will fire a group at the maximum working load then fire another 1 gr below maximum. If accuracy does not improve, I'll split the difference between those two loads and shoot a group half a grain below maximum. If there is no improvement, I'll return to the maximum working load. If the accuracy improved with a load 1 grain below the working maximum, I drop another grain and continue until the improvement drops off, or until I believe the velocity is below my expectation. Once I've got the best accuracy, I'll increase the load by a half grain, then adjust again by .2 grs. I doubt if most of us can realistically improve accuracy with adjustments smaller than .2 grs because there are so many other factors at play. Factors like the uniformity of the volume of our brass, the repeatable accuracy of the powder scale, the concentricity of the case neck, etc, etc. By this time the rifle will be shooting very well, but if you wish some adjustment can now be made to the seating depth of the bullet. Don't get too crazy here because there will be no end to it. Once you've found the sweet spot record your observations, load up some ammo and go shooting.