Some friends have gotten me hooked on long range shooting. There's a great group of folks in Sacramento, the NCPPRC, who have a monthly competition that places you at multiple distances, from 200 to 1,000 yards, away from the targets. Different courses of fire require different positions (prone, kneeling, etc.), make you aim at different areas of the target (head versus body), and sometimes there are barricades or other objects you have to shoot over or around. Oh, and did I mention the wind? It doesn't do much to a bullet out to about 600 yards, but beyond that you have to learn how to read the wind, otherwise you'll rarely hit your target. It's very challenging and a lot of fun.
Most of the common rifle calibers won't reliably and accurately send a bullet 1,000 yards without the bullet falling below the speed of sound. When the bullet transitions from supersonic to subsonic, the turbulance tends to throw it significantly off course. Also, certain calibers were designed to use long, thin bullets that are very stable in flight and buck the wind better than shorter bullets. When I first started long distance shooting I used my .308 hunting rifle. With my hot handloaded cartridges I could reliably get my bullets to stay supersonic out to 1,000 yards, but the rifle wasn't designed to support a scope powerful enough to see that far away, so I needed a more specialized tool.
Enter the Desert Tech SRS-A1. Chambered in .260 Remington and sporting a 26" barrel, this rifle is designed for long distance shooting. The .260 Rem can easily keep bullets supersonic out to 1,200 yards, and those bullets are great at minimizing wind drift. But, as great as the cartridge is, there aren't very many companies who make pre-loaded ammo in it, and when they do it's $2-3 a round. Ouch! This leads most folks who shoot .260 Rem to reload, bringing the price down to a much more reasonable 50-75¢, depending on how many times you can reload each brass case.
When you load your own cartridges, one of the decisions you face is how much powder to use. The reloading manuals give you a safe range to work in, but within that range different rifles may be more or less accurate with different amounts of powder. So, the best way to find out what your particular rifle likes best is to load up a series of rounds with different amounts of powder and see which shoots the best. This process is known as finding the "optimal charge weight."
Thus, over there on the left you can see how I spent my Sunday, looking for the most accurate load in my rifle.
Now, I'm not a superb marksman (yet!), and it's been about three months since I last shot a rifle, but even so we can make out some trends:
The chart shows the accuracy of each group in minutes of angle (MOA), so lower is better. It looks like right around the 45.4-grain area there's an accuracy node that seems to be pretty wide—notice how the accuracy remains nearly the same at 45.7 grains. This means that this is a pretty forgiving charge weight, so a tenth of a grain or so on either side isn't going to significantly reduce my accuracy.
Another interesting point is that my rifle isn't getting a lot more velocity out of the increased charge weights. From lowest to highest I only gained 30 feet per second, so it doesn't seem worth trying to stuff more powder into the cases. My base loads (not shown) using 44.5 gr averaged 2,771 FPS, so going up 0.3 gr to 44.8 gr gave me nearly 40 more FPS, but I had to increase the charge weight 1.2 gr just to get another 30 FPS beyond that. Clearly this rifle isn't going to get much faster with this particular powder.
Anyway, that's what I learned this Sunday, so it looks like now I'm ready to start loading some more rounds!