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Interpeting Magnetospeed Data

 
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Old 02-22-2014, 10:32 PM
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Location: Newark, Arkansas
Posts: 175
Interpeting Magnetospeed Data

So i got my magnetospeed V2 in yesterday and went out this evening to see what the velocity out of my .308 win was.

This is that data I gathered from 15 shots.
Series, 1, Shots:,15
Min,2790, Max,2863
Avg,2829 ,S-D, 19
ES , 73

Series,Shot,Speed
1, 1, 2815, ft/sec
1, 2, 2828, ft/sec
1, 3, 2813, ft/sec
1, 4, 2824, ft/sec
1, 5, 2810, ft/sec
1, 6, 2790, ft/sec
1, 7, 2818, ft/sec
1, 8, 2824, ft/sec
1, 9, 2847, ft/sec
1,10, 2845, ft/sec
1,11, 2849, ft/sec
1,12, 2863, ft/sec
1,13, 2837, ft/sec
1,14, 2847, ft/sec
1,15, 2837, ft/sec

First off, I am seeing some what seems to me, pretty high velocity here, I would like some input on how confident I should be in these numbers.

Also this seems to tell me that my load is complete crap and i need to do some drastic work on getting my ES down.

These numbers were shot out of a .308 win, lapua brass, 175 smk, wlr primer, 44g IMR-4064, 10 thou off lands with a 30 inch barrel. I was hoping to get close to 2800 fps with this gun and 175's but my god, according to the magnetospeed I hit 2863 fps on one shot. And the velocity seemed to increase to the shy side of the mid 2800's after the first 5 or 6 shots. And I had one round at 2790 fps? Should i throw out the outliers?

This rifle has only had 115 shots fired total out of it, is it possible I just experienced some barrel speed up? Are these numbers normal? This rifle shoots sub 1/2 moa consistently at 100, and the few groups I have shot out to almost 600 yards did not exhibit much vertical at all 2 to 3 inches of vertical normally out at 600. Certainly not what i would expect with a 70 something ES. Can anyone tell me what kind of vertical they would expect out of that much ES at 600? Did i just get a few lucky groups?

Thoughts?
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Last edited by Bishop; 02-22-2014 at 11:33 PM.
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  #2  
Old 02-23-2014, 10:59 AM
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Re: Interpeting Magnetospeed Data

Yikes, tough questions I reckon.
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Old 02-23-2014, 11:10 AM
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Location: Near Napoleon,MI
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Re: Interpeting Magnetospeed Data

How fast did you shoot the string ? What were the environmental conditions for this latest shoot compared to when you did the load development ? That powder is temp sensitive and if the barrel and chamber was getting hot, it could increase pressure and thereby velocity. Try the same with Varget and take your time shooting the string. It should be a lot less temp sensitive.
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Old 02-23-2014, 11:46 AM
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Re: Interpeting Magnetospeed Data

I shot all 15 shots over the course of about 2 hours. Environmentals were similar within 15 degrees. From development to now.

Would love to use varget, and will when I manage to get a large enough batch gathered up, I only have 4 1/2 lb's of varget right now vs 18 lb's of imr-4064. Once I manage to get enough varget to have a supply I wont run out of soon I will give it a shot.

The barrel is a 30 inch brux MTU contour I got the barrel ever so slightly "warm" to the touch compared to the ambient temperature with a couple of 3 to 4 shot strings. I didnt get the barrel "hot" by any means.

I suspect I either need to,

1: Back off my powder charge slightly

2:Change to Fed210M primers

3: Change Powder

I guess I am just looking for some reassurance that my magneto isnt lying to me, or having a little brain fart with the seemingly out of place highest and lowest fps shots.
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Old 02-23-2014, 12:46 PM
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Re: Interpeting Magnetospeed Data

Quote:
Originally Posted by Bishop View Post
Min,2790, Max,2863
Quote:
Originally Posted by Bishop View Post
Avg,2829 ,S-D, 19
ES , 73
These numbers were shot out of a .308 win, lapua brass, 175 smk, wlr primer, 44g IMR-4064, 10 thou off lands with a 30 inch barrel.
I donít see anything major that jumps out with what you have listed. Your AVG MV is not unrealistic. ES is high but this may be contributed to your loads and not necessarily the chronograph. I use identical components with a charge of 42 gr. and 20 thou jump in my 30" gun with an average velocity in the 2700s.
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  #6  
Old 02-23-2014, 12:49 PM
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Re: Interpeting Magnetospeed Data

Could the accuracy of the powder scale account for some of that?
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  #7  
Old 02-23-2014, 04:06 PM
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Location: Spokane, WA
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Re: Interpeting Magnetospeed Data

What's your reloading process? are you annealing necks etc.? Bushing or expander ball?
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