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Posted: 2/26/2009 10:41:15 AM EDT
| when you are checking a new ( or old) load for accuracy ,just wondering ,what yardage do you use,100yds, 50yds,or what do you prefer, jim |
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Lets say you are developing a load for a cartridge that will be used at typical ranges of 75-150yd. After looking at ballistics charts for your specific bullet with considerations to its ballistic coefficient and sectional density you come up with a practical zero of 100 yards, which gives you a minimal amount holdover correction for 50 yards and 150 yards...then 100 yards would be the place to start measuring your groups.
For a cartridge like the .223 remington the military (im generalizing here, dont want to turn this thread into a 'well im from such and such and we did it like this' battle) has a 'battle zero' of something like 25 meters. I think thats something like 40 yards but I'm probably wrong. They zero their rifles like that and will basically hit their target point of aim/point of impact up to like 300 meters or maybe further. So for a .223 rem it may be sufficient to evaluate the accuracy of a load at 25 meters. Personally I only have access to a 100yd range so all my targets end up as close to the backstop as possible. My .300 winchester is shooting a 180gr CT silvertip with a muzzle velocity around 2900 fps. The 180gr ct silvertip's BC is .507, and with the tables/charts provided by the mfg. they suggest that for a 100 yard zero I will hit 3.2 inches low at 200 yards, 11.8 inches low at 300 yards, 26.6 inches low at 400 yards, and 48.6 inches low at 500 yards. If i zero at 200 yards I will be an inch and a half high at 100 yards, and 7 inches low at 300 yards. The difference being, with the 100 yard zero I would have to aim 11.8 inches higher to hit a target at 300 yards, or 6.9 inches higher if I had a 200 yard zero. Calculating bullet drop compensation and applying it to your scope's zero may take some time sitting down with a calculator and a clear head, but it will ultimately give you an idea of your bullet's effective range and where it would be most practical to zero your optics and evaluate your accuracy. Some deer hunters I know will take a rifle zeroed for 100 yards, and adjust the elevation so the impact is anywhere from 3"-6" high at 100 yards to compensate for longer range shots..and just remember that anything within 100 yards will be hitting high. (from wiki) MOA is 1.0471996 at 100 yards of distance. MOA is a quadratic effect so 1" of MOA at 100 yards would equate to .5235998" at 50 yards, 2.0943992" at 200 yards, 3.1415988" at 300 yards and so on. Final thoughts: If you are checking accuracy, I'm assuming the rifle is in a mechanical rest to eliminate as much human error possible. If you are shooting with irons 50 yards may be easier on your eyes if you do not have a spotting scope. If you are using optics this isn't an issue. But keep in mind to get the most accurate samples of your ammunition's performance, shot to shot consistancy is important..and 3 shot groups won't give you a fair picture of how your rounds are performing. Try 5-10 shot groups...keeping in mind your initial shot will be a 'fouling' shot or a cold-bore shot and the subsequent rounds may not behave the same way. The bench-rest crowd have all kinds of little things they do to ensure consistancy....sorting their brass and bullets by weight..measuring neck tension...ensuring that the powder in the case is at the base of the cartridge before firing for best ignition by tapping the case or magazine...loading ammunition using the same powder, primer, and bullet lots etc etc. Some of it may seem to border on obsession and at <100yd the difference can be considered negligable...but when you reach out further and further the affects of these variables becomes more drastic. |
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