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Post by zr600 on Dec 9, 2016 12:25:02 GMT -8
Ok I was out at the range today and shot some loads I developed in August now that it's like -3 out is that going to affect my groups big time? At 100 yards they shot good in the cold or warm weather but at 200 they didn't shot worth a darn in the cold but shot .771" group at 200 in august should I look to a different powder for these? The load is 28.4 8208 speed 85g spbt cci 450 2.290 oal. Any help would be great I want something with a higher bc that isn't such a fragmentol bullet.
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Post by peabody on Dec 10, 2016 14:31:13 GMT -8
I'd say the extreme cold can alter your POI, and possibly the overall grouping for your loads.
- Air that cold is extremely dry (change in humidity), which alters the density of the air and the resistance/drag on the bullet, to some extent
- Changes in barometric pressure can make a difference
- Temperature can affect the burn rate of powders, though I believe 8208 is one of the more consistent powders over varying temperatures
- The extreme cold is going to make all of your metal components contract more, and thus expand more once you start shooting and some of the metal parts start to warm up (with aluminum and steel having different expansion rates)... Your cold bore shot is going to be a really cold bore to start with. And temperature can alter harmonics a bit too.
- Lubricants can be more "sludgy" at very cold temps, which makes for more drag between moving parts, despite being lubricated
All in all, many of the effects of extreme cold may be minor when looked at individually. But when combined, the effects can be much more dramatic. If you keep logs/records of your loads and how they perform under various environmental conditions, it can help you create a load library, of sorts, where you can run an optimal load for winter, and another for summer... in theory.
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Post by GLSHOOTER on Dec 10, 2016 14:57:23 GMT -8
The 100 yard distance probably won't be hit by the speed much. 200 can certainly make a change. It is always best to work with what You want in the temps it is going to be seeing if possible. The Extreme powders, listed by Hodgdon, appear to be less sensitive I will never see -3 here but I do see 40 or so and it doesn't appear to matter on the 8208 at 40 -110.
Greg
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