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Posted: 1/8/2009 2:54:55 PM EDT
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I am working up a good load for my SPR type rifle, 1:7 18" WOA SPR barrel. I was testing Varget with a Hornady 75 BTHP today. I had 25 rounds for each charge 23 gr, 24 gr, 24.5 gr. So I fired 5, 5-shot groups, then averaged them together to get an overall average for each load.
Results: 23: terrible, didn't even bother measuring 24: 1.24" 24.5: .670" Best group: 24: .671 (fired 5 shots, but only found 4 distinct holes, I doubt I missed completely) 24.5: .815 So I think I am going to do some further testing of the 24.5 gr load. Does anyone think it's worth it to search out loads by the .1 gr now? I am going to try some 77 gr SMKs next to see what happens with those. |
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If you had chronoed the groups, you'd have seen variations in standard deviation that would have more or less parallelled the group sizes. .5 grain can make a lot of difference in accuracy, not so much in velocity.
Start shooting groups at .1 or .2 difference, and zero in on the most accuate load. |
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Quoted:
I know .2gr made a big difference when I did some 45ACP. 6.5=2inch avg 6.8=1.5 inch avg 7=3 inch avg 7.2= way out there I was suprised.I though more punch would be better.I was @ 6.4gr "better" was a fine line. This squares with my experience. More powder = higher velocity and smaller groups, until you hit the tippint point, where small increases in powder don't add much velocity but group sizes (or std. dev. on the chrono) open way up. The sweet spot is sometimes a bit slower than factory loadings, too. |
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Don't fool around with 0.1 grain increments. Make some loads incremented 0.3 either side of 24.5 to see if you can find a difference.
I would say you're probably as close as you'll get, but what you really want to find now is a robust load in the center of a range of 0.6 grains or so that will shoot nearly the same with any charge in that range. |
| I don't have a chrono because this public range won't let you set one up for some reason. I'm going to try 25 gr and see if the groups start to open up. If they do I'll do something around 24.7 and see what happens. Also still going to try the SMKs and see what they can do. The Hornady bullets are good, but who knows if the SMKs will work better. |
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