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Rifles, Reloading, Optics, Equipment
Reloading
Accuracy lost on warmer weather
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<blockquote data-quote="Joe-boy" data-source="post: 2847697" data-attributes="member: 113266"><p>Any thoughts from the more experiences ones? Executive summary: groups nicely in the cold and crappy in the summer heat.</p><p></p><p>2-3 years ago I developed a load for 53 grain Hornady v-max for my .223 chambered CZ 527 that has an 1:12" barrel. I developed the load in the wintertime around freezing point and was relatively happy with how it worked. I used it for raccoon dog hunting and plinking for a while, until last summer I went shooting on a very hot day (around 30 deg C or 86 deg F) and got crappy groups. Like real crappy, around 2-3 MOA at 100 meters. I just thought I had screwed up something the previous time when developing the load and hadn't tested it properly and didn't think about it that much. I had not much of those left so I shot them away and proceeded to develop a new one with different brass.</p><p></p><p>This time I again got a load that grouped nicely below freezing point. From my archive I was able to find e.g. a 8 shot group of 0,66 MOA that wasn't cherrypicked but was pretty consistent with how it grouped; also 8 shot group already proves a bit more than cherrypicked 3 shot groups. Forward 6 months; I went to range when the temperature was about 20 deg C = 68 deg F. Again really crappy grouping. My 13-shot group was 2.3 MOA and doesn't get much better by excluding a flyer or two; it was consistently crappy. The bullet holes are nonetheless nice and round.</p><p></p><p>The load is developed using a ladder test and is using Lapua Match brass and Vihtavuori N133 powder which shouldn't be too temperature sensitive.</p><p></p><p>I guess there are basically two alternatives: either the muzzle velocity or the muzzle time changes enough to somehow screw up the barrel harmonics, or then the stability is compromised as the 53gr vmax is quite a long one for a 1:12" twist. However, I'd assume the stability should be better in the summer with the thinner air and probably increased muzzle velocity.</p></blockquote><p></p>
[QUOTE="Joe-boy, post: 2847697, member: 113266"] Any thoughts from the more experiences ones? Executive summary: groups nicely in the cold and crappy in the summer heat. 2-3 years ago I developed a load for 53 grain Hornady v-max for my .223 chambered CZ 527 that has an 1:12" barrel. I developed the load in the wintertime around freezing point and was relatively happy with how it worked. I used it for raccoon dog hunting and plinking for a while, until last summer I went shooting on a very hot day (around 30 deg C or 86 deg F) and got crappy groups. Like real crappy, around 2-3 MOA at 100 meters. I just thought I had screwed up something the previous time when developing the load and hadn't tested it properly and didn't think about it that much. I had not much of those left so I shot them away and proceeded to develop a new one with different brass. This time I again got a load that grouped nicely below freezing point. From my archive I was able to find e.g. a 8 shot group of 0,66 MOA that wasn't cherrypicked but was pretty consistent with how it grouped; also 8 shot group already proves a bit more than cherrypicked 3 shot groups. Forward 6 months; I went to range when the temperature was about 20 deg C = 68 deg F. Again really crappy grouping. My 13-shot group was 2.3 MOA and doesn't get much better by excluding a flyer or two; it was consistently crappy. The bullet holes are nonetheless nice and round. The load is developed using a ladder test and is using Lapua Match brass and Vihtavuori N133 powder which shouldn't be too temperature sensitive. I guess there are basically two alternatives: either the muzzle velocity or the muzzle time changes enough to somehow screw up the barrel harmonics, or then the stability is compromised as the 53gr vmax is quite a long one for a 1:12" twist. However, I'd assume the stability should be better in the summer with the thinner air and probably increased muzzle velocity. [/QUOTE]
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Accuracy lost on warmer weather
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