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-   -   How will the summer heat affect... (http://www.firearmstalk.com/forums/f30/how-will-summer-heat-affect-85358/)

Tenderribbs 02-27-2013 09:42 PM

Affect my groups that I have developed during this winter? I always reload in the house so the ammo has maybe 2 minutes to get outside temp before I shoot a 3 rd group, so say from inside at 70 to outside at about 35 to 40. Would I have to use a touch less of powder in the heat to get the same sub MOA groups that I developed this winter ? Is there a " in General rule that applies ? Thanks

JonM 02-27-2013 10:17 PM

only way to tell is by trying em.

each rifle is going to react differently to weather conditions and ammo build. just write down your winter recipe and try it and see if it sucks in summer start building a summer load.

sometimes thats all you can do.

Sniper03 02-27-2013 10:56 PM

Ribbs,

JonM, Is correct! Each rifle if you call it will have it's own personality regarding conditions so you will have to see.
As far as loading it in the winter in 70 degrees and going immediately to the range and shooting it without it being exposed to the elements or direct sun light and heat. It probably will make little difference. But if it remains in the heat for a period of time long enough to allow the temperature of the round to change it certainly can cause a difference. Usually normally due to the following. *I have on occasion but not often, seen effect on the group.
As a rule the consensus is that if at the location the altitude, barometric,humidity stay the same. Increase in air temperature (ammunition warming up!) will usually cause the rounds to fly flatter due for one, if the air gets hotter it is less dense. And in the case of internal ballistics the round getting warmer the higher temperature causes the Nitrocellulose in the powder to burn at a faster rate. Therefore generating an increase in pressure. For example some studies have shown that an increase 1.5 to 1.8 degrees could increase the flight of the bullet to +3.5 Feet Per Seconds. So as an example a 40 degree increase of the cartridge heat (As left exposed to sun light) could increase the flight of the bullet in the case of the 3.5 FPS to that of 140 Feet Per Second. So this is just an example of the effect of temperature. Obviously colder would have an opposite effect. But Jon refered to testing is required as stated and each particular rifle has different effects.
But if you load them at 70 degrees in the winter and you zeroed the rifle in that temperature range by putting them in a pocket or bag and go straight out and shoot them you should notice little difference at all. But let them heat up or cool down significantly and then the above applies.
03

Tenderribbs 02-27-2013 11:31 PM

Thanks sniper and Jon that's the type info I'm interested in .

Txhillbilly 02-28-2013 03:54 AM

Some powders are temperature sensitive,and they will do weird things.
I've had some loads for my 458 SOCOM that I developed in the summertime,they shot sub-moa - But come fall,and the temps were 30-40 degree's cooler,the same loads had pressure signs,and shot 3-4 moa. So I had to rework the load for cooler weather,I dropped the powder charge .6 or .7 gr to get the pressure down,and it shoots well,but not near as good as the warm weather load.

locutus 02-28-2013 01:28 PM

Quote:

Originally Posted by Txhillbilly (Post 1157478)
Some powders are temperature sensitive,and they will do weird things.
I've had some loads for my 458 SOCOM that I developed in the summertime,they shot sub-moa - But come fall,and the temps were 30-40 degree's cooler,the same loads had pressure signs,and shot 3-4 moa. So I had to rework the load for cooler weather,I dropped the powder charge .6 or .7 gr to get the pressure down,and it shoots well,but not near as good as the warm weather load.

There are several factors. Wood or synthetic, full bedded or free float, but in my experience the powder is the primary controlling factor.


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