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7mm ultra

 
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  #1  
Old 04-03-2009, 12:19 AM
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Join Date: Dec 2008
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7mm ultra

Hi, ran into a new problem. I am reloading my 7mm ultra in a remington sendero. I wanted to match factory ammo (3400 fps w/ 140 gr. nosler) Here are my results with reloader 25:

90.5 gr = 3225 fps
91.0 gr = 3202 fps
91.5 gr = 3224 fps
92.0 gr = 3281 fps
92.5 gr = 3280 fps
93.0 gr = 3459 fps

Any one know why with more powder there is less fps? Or why the jump of 180 fps with only .5 gr more?

Next problem. The 93 gr load was the most accurate load. It was a one hole group with 5 shots (this was the only load that matched factory ammo for groups). However, the brass was a little shinny on the bottom (no sticky bolt or other signs of pressure). I shot the rounds at 45 degrees. Would this load be dangerous at 95 degrees on a antelope hunt.

Thanks for your thoughts.
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  #2  
Old 04-03-2009, 11:48 AM
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Join Date: May 2008
Location: South of Canada and North of Wyoming
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Re: 7mm ultra

If those are single shot velocities at each wieght, then you are going to get some deviation in velocity. In other words, If you shoot 3 rounds of 90.5 gr, you might get speeds of 3184, 3198 and 3225 with an average of 3202. And if you shoot 3 at 91 gr you might get 3202, 3221 and 3230 with an average of 3218. Chronographing just one shot at each weight doesn't give you a good picture. Now if those are averages fo 3 shots or more, then that would be odd. You also want to make sure your chrony is set up good with good batteries.

On your 93 gr load, I think you'll probably be ok at 95 degrees but that might be pushing it. In anycase, it shouldn't be "dangerous", but you might want to work up to it with some lesser loads just to make sure.
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  #3  
Old 04-03-2009, 08:14 PM
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Re: 7mm ultra

Hey Montana thanks for the reply. Those were 5 shot averages. I am sure my chrony is good, replaced the batteries in feb, and I agree it is odd. The most disturbing is the huge jump between 92.5 gr and 93 gr.
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  #4  
Old 04-03-2009, 11:42 PM
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Re: 7mm ultra

I have experienced discrepencies in velocities before too. did you allow the barrel to cool between groups totally? Was the temperature the same? was seating depth the same? Was the cloud cover the same (affecting your chrony). I don't have a real expensive chrono, and I made up my mind that I will only use the chrono to make drop charts using an average of at least 10 rounds on a few occasions for test. I don't really understand myself why the numbers seem to jump sometimes.
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  #5  
Old 04-03-2009, 11:55 PM
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Re: 7mm ultra

I would have the same questions as Britz. Sounds like it could be just about anything. I would consider the light conditions for the chrony first, then load developing procedures, and compenents.

It would be interesting to see all 5 velocities at each weight increment.
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  #6  
Old 04-04-2009, 09:24 AM
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Re: 7mm ultra

If you are having pressure issues at 45* I think they are going to be a lot worse at 95. Only way to know for sure though is to shoot them on a 95* day. What was the ES on the 93 load ?
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