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.270 velocity variations

 
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  #8  
Old 12-09-2009, 11:42 AM
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Re: .270 velocity variations

Some powders will just vary quite a bit. When developing loads for my 1k competition rifles I use the Denver Instruments but the Charge Master works close enough.

If you are leaving the unfired cartridge in a warm or hot chamber for more than a few seconds this will also contribute to your problem. Too many variables to go into here.

Think you are barking up the wrong tree here imho.
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  #9  
Old 12-09-2009, 11:49 AM
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Re: .270 velocity variations

yep
H4350 RL22 and Varget in the .243
Thats why this whole thing is driving me nuts!!
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  #10  
Old 12-09-2009, 11:54 AM
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Re: .270 velocity variations

Things I think about for extreme ES...

powder charge as has been discussed
primers (use of benchrest primers has narrowed ES in my hands)
neck tension- are you turning necks to achieve consistent neck tension?
brass uniformity
environmental factors (heated barrels etc)
accuracy of chronograph
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  #11  
Old 12-09-2009, 03:33 PM
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Re: .270 velocity variations

I don't have a neck turner.....yet. I can see accuracy...but velocity?
I have thought about the chrony...but how do you verify a chrony??
I have been shooting bench rest primers. I got 5 bricks just before the crunch hit.
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  #12  
Old 12-09-2009, 07:50 PM
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Re: .270 velocity variations

Neck turning is a bit of a stretch, but I found that with necks turned to the same thickness, I was able to achieve the same neck tension on each bullet and I felt like the velocities seemed to be more consistent. To clarify, this was by neck sizing only without an expander ball on unturned brass. Probably related to different chamber pressures in the bullets with thicker necks and tighter neck tension??? This may or likely may not apply to you and also would only be responsible for small variation not 100fps variation as you describe.

I have asked about chrony verification in the past with not much help. The only thing you can do is set two different models end to end and shoot over each (at the same time) to see how close the readings are with each shot. This gives you relative data (not absolute), but I haven't heard of a place to send in your chrony to have it validated. Don't really need to worry about this if your drop data matches your chrony's numbers. Sometimes the light here in New Mexico plays heck with my chrony. 100 fps might mean a difference in 20-30 inches at 1000 yards. If you are truly getting that variation it would certainly be evident at long ranges. Probably barely detectable at 100 yards?

Lucky you on the primers! Hope to see an end to this shortage soon.
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  #13  
Old 12-10-2009, 09:15 AM
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Re: .270 velocity variations

Quote:
Originally Posted by kstrick View Post
I understand Retumbo is very consistent but I do not find any info for the .270. Has anyone tried it??
Thanks
Ken
I think you will find Retumbo is too slow burning to be an effective performer in the 270.

Shot to shot variations in velocity can often attributed to certain powders in certain cartridges. Years ago I tested RE22 with 100gn bullets in my 243 and velocity varied by as much as 120fps. When I went back to H4350 shot to shot variations went back to a more acceptable 20fps-30fps.

The same can be said when I tried W748 in my Marlin 444 - velocity was all over the place. Once I went back to H4198 velocity variations shrunk to single digits.
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  #14  
Old 12-10-2009, 09:55 AM
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Re: .270 velocity variations

Thanks for the advice.
I have pretty much settled for H4350 for my .243 as well. I get consistent velocities as well.
Thanks
Ken
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