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Weird Velocity Readings

 
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  #1  
Old 08-04-2013, 07:23 PM
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Join Date: Mar 2013
Location: Nebraska
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Weird Velocity Readings

Went out to the range this morning to run some test loads out of my 280 Rem (Browning X-Bolt / 22'' barrel) and had some really weird readings thru my chrony.

Some quick info on the loads:

All 4-fired Winchester brass, full length sized and trimmed to 2.530''.

4 sets of 3 rounds loaded with 53.5 gr. of IMR-4350.

140 gr. Sierra Gameking (0.2 gr. over max according to Sierra's manual / 0.5 gr. under max per Lyman 49th edition.)

Set #1: 0.040'' off rifling / velocities: 2789, 2818, 2800 / 0.277'' group (one ragged hole)

Set #2: 0.035'' off rifling / velocities: 2694, 2804, 2982 / 0.384'' group (one ragged hole)

Set #3: 0.025'' off rifling / velocities: 3006, 2857, 2838 / 1.095'' group

Set #4: 0.020'' off rifling / velocities: 2826, 3114, 2592 / 6.988'' group (not a typo)

I had no pressure signs with any of the sets. Chronograph was set 12' from the muzzle and it was partly cloudy out (60 degrees).

I tested this same bullet & powder charge a couple days ago with pretty consistent chrony readings (2856, 2847, 2865 fps). Bullets were seated 0.030'' off of the rifling on this set.

I would love to get consistent 3000-3100 fps with this bullet, but I can't find a single load in 3 different manuals (Hodgdon, Sierra, or Lymans 49th) that will yield these kind of velocities without loading way over max.

I'm stumped. Does anyone have a thought as to why I'm getting these spikes in velocities?
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  #2  
Old 08-04-2013, 08:18 PM
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Re: Weird Velocity Readings

What kind of scale do you use...if balance beam could it be sticking?
Is the battery newish in the chrono?
Either the chrono is screwing up or the powder charges are.
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  #3  
Old 08-04-2013, 08:22 PM
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Re: Weird Velocity Readings

I'm using an electronic scale...each load is weighed. I check the electronic against a balance every so often, usually the first couple of loads per session. It always checks out fine.

The battery in the chrony is brand new.
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Old 08-04-2013, 08:26 PM
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Re: Weird Velocity Readings

First thing I'd suggest is set screens to chronograph out a little further to at least 15 if not 20 feet.
Second thought is 4350 is too slow burning for 22 inch barrel and your not getting consistent complete burning of powder charge resulting in wide variation of fps.
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Old 08-04-2013, 08:43 PM
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Re: Weird Velocity Readings

Quote:
Originally Posted by 375fan View Post
First thing I'd suggest is set screens to chronograph out a little further to at least 15 if not 20 feet.
Second thought is 4350 is too slow burning for 22 inch barrel and your not getting consistent complete burning of powder charge resulting in wide variation of fps.
What powder would you suggest?
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  #6  
Old 08-04-2013, 09:25 PM
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Re: Weird Velocity Readings

My brother has been shooting 280's since he got out of diapers it seems and he's always at/over 3K fps with a 140 in a 22" pipe and usually nipping at 3050 fps.
He's using rl22 in a remmy with a 140 ct on top at present.
Top load for rl22 in the 2005 Alliant data for the 139 hornady is 59.5 rl22 at 3000 at 57.5 kpsi peak with a rem primer and remmy brass. I've seen him make some shots with that cal. that I likely wouldn't attempt and I'm a showoff behind a rifle.

ps. listen to 375fan on the chrono; you are likely either seeing the powder blast or getting double shadows from the sun angle if it's a low sun angle.
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  #7  
Old 08-04-2013, 09:38 PM
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Re: Weird Velocity Readings

Quote:
Originally Posted by Lefty7mmstw View Post
My brother has been shooting 280's since he got out of diapers it seems and he's always at/over 3K fps with a 140 in a 22" pipe and usually nipping at 3050 fps.
He's using rl22 in a remmy with a 140 ct on top at present.
Top load for rl22 in the 2005 Alliant data for the 139 hornady is 59.5 rl22 at 3000 at 57.5 kpsi peak with a rem primer and remmy brass. I've seen him make some shots with that cal. that I likely wouldn't attempt and I'm a showoff behind a rifle.

ps. listen to 375fan on the chrono; you are likely either seeing the powder blast or getting double shadows from the sun angle if it's a low sun angle.
It's funny you mentioned R-22. I'm getting 2950 fps with 56.8 gr. of R-22 behind a 140 gr. Barnes TSX with 0.75'' groups, so I loaded up some 140 gr. Sierra Gamekings & R-22...the velocities were horrible. I figured too slow of powder for a 22'' barrel with the Gamekings, so I switched to IMR-4350.
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