Posted: 1/26/2015 2:01:20 AM EDT
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I ask because I shot my first reloads today. My gun is a Savage model 10TR that loves FGMM 168s and 175s.
My loads today were: IMR 4064 42.0, 42.5, 43.0, and 43.5gr CCI LR primers Federal Brass trimmed to 2.012 2.800 OAL The 42.0 shot a 0.380 group at 100yds, then the 42.5 opened up to 1.07, the 43.0 was 1.36, and the 43.5 was 1.60. Temperature was 53*F. Would those 0.5gr changes cause that much change in group size? I wouldn't think it would. I can blame shooter error, and I was shooting suppressed which causes a lot of mirage in my scope and the reticle was "floating". My next loads will be 41.0 - 42.2gr. Hopefully I'll get some good results. |
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I shoot a Benchrest match once a month with a Savage 10 308.
My best load is 40.5 of 4064 using 168 gr SHPBT match bullet and .010 off the lands. Best 5 shot Grouping at 100 yds was .316 won smallest overall group and my class. Have used a 155 gr with 42.0 of 4064 but found the 1-10 twist of my barrel likes the heavier barrel. |
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Quoted:
Almost zero conclusions can be drawn from one group. Posted Via AR15.Com Mobile There is a lot to be said about the above but if you find a pattern it can be helpful. .5 grains is a decent step except for the really big magnums. I look for the roller coaster, small to big to small to big. I also look for the small groups to have similar impact points on charges either side of them. Those are the easy to keep in the zone loads with a lot of tolerance to small variations. |
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I just did an OCW test with .4-.5gr increments, and found that the groups "roller-coastered" from .4 to 1.3 moa several times between 39-45gr.
Interestingly, the best charge weight in my test was right at 40.4gr (imr 4064 under a 168amax), which is right on par with a previous poster's best load. If you Google "OCW and OBT" you will find a very interesting article from 2003-2004 discussing how dwell time in the barrel affects group dispersion. It's about the strain in the barrel causing the bore to enlarge and contact very small amounts depending on where the "shockwave" is when the bullet exits. This can cause the groups to open up or tighten with relatively small changes in powder charge, whereas the POI shift with respect to POA tends to "walk around" more slowly, and is due to barrel whip (longitudinal strain in the barrel as opposed to lateral strain). Very interesting read. |
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It is easy to fool oneself
How many shots in each group? How many groups of each load? Which order did you shoot them . How long between shots? A barrel that is too clean , too dirty , too cold , too hot , may shoot different . A bullet/load that may shoot excellent out at 200 , 300 or longer may be strongly unimpressive at 100 . The long range gurus claim many great loads take some distance to "settle down" |
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Quoted:
A bullet/load that may shoot excellent out at 200 , 300 or longer may be strongly unimpressive at 100 . The long range gurus claim many great loads take some distance to "settle down" I was thinking about that. For example, my 43.0gr loads shot 1.3 MOA at 100, but sub MOA at 400 (3.38 inches to be exact). |