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What is an acceptable change in velocity with a change in temp

 
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Old 08-05-2012, 01:13 AM
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Join Date: May 2012
Location: Oregon (the motherland)
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What is an acceptable change in velocity with a change in temp

Brand new to long range hunting, been doing load development for my 300 RUM the last few weeks. Current load is 215 berger hybrids, nosler brass, fed 215m primers, and 89.5 grains H1000. Today it was 80* to start, speeds were 3100 fps with an es of 3. We were shooting in the blazing sun and kept track of how warm the rounds were getting, ended up at 110* and the speeds were 3160 with an es of 17. Being new to this, I would like to know if this is normal/ acceptable range. Trying to test the load in a variety of conditions. Any help is greatly appreciated
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Old 08-05-2012, 02:50 AM
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Re: What is an acceptable change in velocity with a change in temp

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Originally Posted by tslesquire View Post
Being new to this, I would like to know if this is normal/ acceptable range. Trying to test the load in a variety of conditions.
I don't use that powder but I would think it could be "normal." It is up to you as to, if it is "acceptable."

I have a winter load that is stable until it gets above 32 F; then the POI shifts high and left. My summer load with the same components remain stable at up to 95 F; then goes high right. The temperature doesn't usually get beyond 100 F here, so I'll accept that I'll need to remember the summer load's POI shift; as well as to bring a summer load in winter, just in case.

This is where a logbook comes in handy, to record all conditions for all shots.
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Old 08-05-2012, 10:47 AM
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Re: What is an acceptable change in velocity with a change in temp

I don't know if there is anything you can really do about it.
Not only does powder/primer temp influence results, but so does barrel/bore dimensions.
There may also be contribution of differing lighting to your chrono screens.

What I do to reduce the issue is pull every shot from a pants pocket. This, while load developing and when in the field, regardless of temps summer or winter. But I can imagine this would not be practical with 300RUM..
My thinking is, rather than trying to cool ammo, which is logistically difficult and causes condensation below dew point, I can keep it near body temp pretty much all year long.
I'll pull it out of my arse if I have to(but not with 300RUM).

I'm working on a temp controlled/heated ammo box for the bench, that single shot dispenses(that's the tricky part). A better design would allow practical use in the field as well(tricky part II). If I develop something of value, I'll bring it here for all to benefit.
R&D...........
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Old 08-10-2012, 02:57 PM
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Join Date: Mar 2008
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Re: What is an acceptable change in velocity with a change in temp

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Originally Posted by Mikecr View Post
I don't know if there is anything you can really do about it.
Not only does powder/primer temp influence results, but so does barrel/bore dimensions.
There may also be contribution of differing lighting to your chrono screens.

What I do to reduce the issue is pull every shot from a pants pocket. This, while load developing and when in the field, regardless of temps summer or winter. But I can imagine this would not be practical with 300RUM..
My thinking is, rather than trying to cool ammo, which is logistically difficult and causes condensation below dew point, I can keep it near body temp pretty much all year long.
I'll pull it out of my arse if I have to(but not with 300RUM).

I'm working on a temp controlled/heated ammo box for the bench, that single shot dispenses(that's the tricky part). A better design would allow practical use in the field as well(tricky part II). If I develop something of value, I'll bring it here for all to benefit.
R&D...........
Why couldn't u just use a 1 pound propane tank and a radiant heater of some type? Then it wouldn't need electricity and it would be small. I dont know what you mean about single shot dispenses - maybe thats y u said tricky part. You need to make it heat evenly that is the problem im having. if you could some how "turn" the bullet or have a radiant heater on both sides. Who makes "small" radiant propane heaters? If you use body heat you would have to use primer sealer to keep humidity "in check" as long as that stuff didn't "hurt" the bullet release. That stuff isn't that strong is it? the best would be if you used a radiant heater and a little battery to rotate the bullet like on that one fancy annealing machine. Then you would need just one heater and a battery. I know you can go even smaller with at little camp fire stove but now we have open flames etc. Lots of possiblities here. I have been working on some stuff for shooting and would like to know how your R&D goes. How hot should we make it? Does 300 - 450 F sound good enough?
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