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Posted: 8/28/2008 7:07:50 AM EDT
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I've been reloading off and on for 20 years, but until now never had a chronograph. I would work up rifle loads by .5 grain increments until I got to a load with a small group, & then the loads would start to open again. I'd then "tweak" the load with the smallest group in .1 grain increments to get it as tight as possible. I think this is a pretty "standard" practice. Well I've been working on some loads for one of my AR15's. I have two loads... 53 gr & 68 gr. that both are at 1" at 100 yds, in a very neat concentric circle. I'd say I'm on the right track... but here's my dilemma. The extreme velocity spreads are 93 fps w/ 53g load & 106 fps w/ 68g. That is with 10 shots each. If I take the 2 most extreme out & use 8 shots, it drops to 58 fps w/ the 53g load, and 77 fps with the 68g load. That seems like a lot, and tells me the loads could be really good if I could get them more consistent. All cases are same brand, trimmed to same length, necks chamfered & deburred. Each charge is weighed (H335 for the 53g & Rel 15 for the 68g), the bullets are match. I did not weigh the cases, or the bullets. I will do that for the next test to see if there is much variation. Never having had a chronograph, I don't know what to expect. I found 1 article that said 20 fps extreme spread was getting into match grade zone. I'm looking for pointers as to where to adjust. Is the powder bullet/choice the issue? I think my cases look good & consistent as far as prep. I'm using CCI 400 primers... not bench rest or match, could they be the cause? Or as I vary the charge weight to refine the load, is it common to get more consistent? I know all the above can contribute, but I'm looking for some insight from the guys with a little more experience to shed light on what to expect, and what to look for. |
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Try switching primers. Rem 7 1/2, CCI BR-4's, or Fed 205's or 205M's. Uniform the primer pockets and deburr the flash holes. Consider a die that will let you control neck tension, either a bushing die, a standard die with a modified expander ball (or no ball), or a Lee collet die with the mandrel adjusted to the diameter needed. You ate from the fruit and gained knowledge you didn't need by buying that chronograph! Your loads will hold up fine out to several hundred yards with that spread. But, I've never had much trouble getting the ES down to about 20 fps with the primers above, match grade bullets, RE-15, and Winchester cases. The cases were not weighed or neck turned, but the primer pockets are uniformed and the flash holes deburred. For .223 Rem, I use a Redding neck bushing die. New brass is usually sized with a 0.245 inch bushing. |
| Your chrono results do not surprize me. My tightest AR loads were not nearly the best through the chronograph; many others have also experienced this. My bolt gun results are a different story. I can get them in the single digits and they will be the best groupers. |
I see this often myself, higher SD and good accuracy. Oh well, I'll take accuracy over small SD's. Of course a small SD would probably eliminate some vertical dispersion at 600-1000 yards. In theory anyway. |
| I have also had success experimenting with overall length. Some of my rifles like the cartridge longer than usual with some bullet engraving occuring on full battery while others will do better with the bullet set back further than usual. Of course with the AR or hunting rifles magazine length is often the best indicator of OAL... |
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