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Old 01-04-2013, 17:06   #1
Fwdftw
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Need some help with this Data Vs Chrony

Okie dokie this off of Ramshots Site

TAC 62 MIL M855 min 23.6gr 2,940FPS
max 26.2gr 3,219FPS OAL 2.260

Im loading m855 62gr at 23.5 2.220 OAL and only averaging 2650FPS Std Deviation is 35. Why is this so off?

Same with my SMK 69gr Load

Ramshot Data
TAC 69 SIE HPBT min 22.9 2,775
max 25.4 3,049

My load 23.5gr TAC 2.220 averaging 2627 std deviation also around 35
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Old 01-04-2013, 17:21   #2
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Barrel length is huge with rifles. Are you using the same length barrel?

Also, rifles tend to vary more gun to gun than pistols. All the aspects of chamber dimesnsions, rifling type, smoothness of bore, case volume and on and on seem to make more of a difference in rifles. Maybe not as a percentage, but certainly in terms of the shear fps difference between guns with the same load.

Also, manuals seem to be a bot optimistic at times. Some are better than others.

And to further screw you up, I actually get much higher velocity in my 30-06's than the Hornady manual says I should be getting, and with shorter barrels. Go figyah!
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Old 01-04-2013, 17:57   #3
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This is how guys get into trouble with their chrono. Read the bbl length, it's 24", so figure 50fps/inch loss w/ the 223. In a 16" carbine, you are just about right there. As WT notes, all rifles are diff, so you can have identical rifles 100fps apart w/ the same load.
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Old 01-04-2013, 19:00   #4
Fwdftw
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So fred your saying

the min velocity on my SMK load is 2775 minus the length of my barrel 16inch vs 24inch that would be a loss of 8*50=400 so Minimum is 2375

Max before bbl length is 3049 minus the 400 for bbl length is 2650 ?
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Old 01-04-2013, 21:05   #5
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Anyone lol

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Old 01-04-2013, 23:22   #6
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Quote:
Originally Posted by Fwdftw View Post
So fred your saying

the min velocity on my SMK load is 2775 minus the length of my barrel 16inch vs 24inch that would be a loss of 8*50=400 so Minimum is 2375

Max before bbl length is 3049 minus the 400 for bbl length is 2650 ?
Yep, +/- 10fps or so per inch. Diff powders & bulelts will vary a bit. Some bbls are a bit slower or faster than others, so it's a ball park vel number. Just don't keep putting powder in trying to reach the book chrono numbers like a buddy of mine did when he first got his chrono. Just doesn't work that way.
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Old 01-05-2013, 10:09   #7
Fwdftw
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So if i have good accuracy with the load stick with it.

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Old 01-05-2013, 11:03   #8
rsrocket1
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Quote:
Originally Posted by Fwdftw View Post
So if i have good accuracy with the load stick with it.
That's what really matters isn't it?

If you found a load with good accuracy and haven't exceeded the max load, you are good to go. Your SD is just over 1% which is also good.

You'll be good out as far as you need and if you regularly need more range, get a longer barrel.
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Old 01-06-2013, 01:23   #9
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Quote:
Originally Posted by Fwdftw View Post
So if i have good accuracy with the load stick with it.

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Proof is always in the shooting. While a SD of 35fps can be improved upon, if the load shoots well, why bother? I have had low SD loads NOI shoot as well as higher SD loads. Out to 300yds, low SD means little. Typically, SD will go down as you increase load density & get pressures up, especially as powders get slower.
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