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Temp sensitive powder and fps ?

 
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  #8  
Old 12-10-2013, 09:38 AM
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Location: Meridian, Idaho
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Re: Temp sensitive powder and fps ?

Thanks. That is nice and easy method. I measured it last night and 2.0 was pretty much dead on. I had just thrown in a number originally based on experience with such combos but had not confirmed it. Following the shiny object made me forget.

I think 3600 is probably close. I will shoot drop again when I go back out. The POI at 6.75 MOA is close to 2.75 low from POA. If I come up .5 to 7.25, based on measuring the target 3600 is getting me quite close. I can fine tune from there.
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  #9  
Old 12-10-2013, 01:20 PM
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Re: Temp sensitive powder and fps ?

Do you chronograph your loads?If not you will be chasing your results 'till Kingdom Come. From your post I gather you are estimating your MV.

All recent production IMR powder is "Extreme" Technology. Doubt temp is an issue. Back when the NRA tested this they used 4895, 4350, and 4831 -surplus. The 4831-surplus was bad. But the 4895 wasn't too extreme, about 80fps as I recall. But this is not your problem.

You have to have an accurate (<1% preferred) Muzzle Velocity to start. So buy, beg, borrow a chronograph.

But from your results I would guess your BC figure is wrong, that it is not what the bullet maker claims (surprise, surprise!). I use Sierra GK and MK for most of my shooting and their BC's are very accurate. That is not true for every maker. Because High BC bullets sell better the #'s are inflated. When you side by side the bullets and two are pretty much identical then how is it they vary so much in BC?

Many posts to this website have commented on reducing the BC # to conform the data to the prediction of the Ballistic Programs. I bought a second chronograph to get down range velocity (on the same shot, each shot) to get an accurate BC. I believe this is your problem.

Hope others will chime in on this. Dialing in your data is what it is about. Lots of experience on this site doing just that.

KB
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  #10  
Old 12-10-2013, 01:36 PM
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Re: Temp sensitive powder and fps ?

Re read you original post. Your chrono not reading is a problem. But you need to check the actual speed at 7F degrees. Hard to believe it is -200fps.

Sometimes shooting MUCH closer to the screens helps. My 45's read every shot. The 556 needs to be no more than 6" above the slits and dead center. I built armored sleds for my chronographs so I don't hammer them when I do this.

Huge density altitude change between your two range sessions. The cold one may have been at or below sea level DA. 55F @ 4500' altitude may be close to standard conditions. Dial in the changes in conditions and see how close it conforms.

Finding solutions to this sort of thing is the both frustrating and fascinating thing about this hobby. Kind of like women.....

KB
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  #11  
Old 12-10-2013, 03:06 PM
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Re: Temp sensitive powder and fps ?

I shot the 204 at 10ft off and between the 4 and 6" mark on the chrono. I don't mind doing it old school via drop confirmation either. I like to do both. BC of the bullet would have to be considerably off for it to make a 6.5" low impact.

For example if I left the 3800MV in the solution and tweaked BC it would be .230 vs the .275 or about 21% off. Now, looking at Berger 40, Nosler 40, and Sierra 39, I see the numbers all over the freaking place. Berger is the lowest of the group and Sierra the highest.

Any thoughts on the .275 BC of the vmax vs .225 of the Berger or .239 of the Nosler? Sierra is .287.
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  #12  
Old 12-10-2013, 06:14 PM
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Re: Temp sensitive powder and fps ?

Go with the BC. But I would shoot over the chronograph every time if possible. I do and the numbers always mean something.

I'm guessing the BC listed is in fact BS. Try three different ranges w/ same zero. Check the BC change against that info.

A lot of shooting but someone has to do it!!!

KB
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  #13  
Old 12-10-2013, 06:24 PM
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Re: Temp sensitive powder and fps ?

I will dig the chrono out and shoot over it again as well as shoot the different ranges. I wanted to do it anyway to confirm drop data as well figure out the BDC reticle of the scope for quick reference if time to dial is not optional. This scope has the Boone and Crocket reticle and now M1 turrets. Hope it is reliable.

Thanks.
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  #14  
Old 12-10-2013, 09:11 PM
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Location: Washington State
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Re: Temp sensitive powder and fps ?

Do you realize how fine the adjustments have to be made accurately to move POI @ 100yds exactly 1"? Check the scope for movement per click. Use ten clicks round robin - ten up, ten right, ten down, ten left. Measure and divide.

I don't expect scopes to be dead nuts on POI changes. Consistent yes, but exact? No Way! Too hard to machine. Unrealistic expectation.

KB
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