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7 saum unexpected velocity

 
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  #8  
Old 04-10-2012, 12:48 AM
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Join Date: Mar 2012
Location: BLACK HILLS SD
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Re: 7 saum unexpected velocity

Shot some 162 amaxs i had loaded over the chrony today and got anywhere from 3160 to 3295. This is with 56.0 grains of h4350 and cci 250 primers. It doesnt seem like there is any sign of high pressure. No hard bolt lift and the primers still have nice round edges. This load is decent at 100 but obviously wont work with distance. I am planning to try some regular primers any try to get the extreme spread under control. Not sure if the keg of powder i have is giving me the extra speed or if it is the barrel. I have not tried any other powders with this gun yet.
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  #9  
Old 04-10-2012, 07:42 AM
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Re: 7 saum unexpected velocity

Quote:
Originally Posted by XTRTITAN View Post
Shot some 162 amaxs i had loaded over the chrony today and got anywhere from 3160 to 3295. This is with 56.0 grains of h4350 and cci 250 primers. It doesnt seem like there is any sign of high pressure. No hard bolt lift and the primers still have nice round edges. This load is decent at 100 but obviously wont work with distance. I am planning to try some regular primers any try to get the extreme spread under control. Not sure if the keg of powder i have is giving me the extra speed or if it is the barrel. I have not tried any other powders with this gun yet.
With spreads like that, I would still be suspicious of the chrono.....Rich
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  #10  
Old 04-10-2012, 05:44 PM
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Join Date: Apr 2010
Location: Allen, TX
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Re: 7 saum unexpected velocity

Your data doesn't add up.
You may have multiple problems... with JBM and/or the chrony
e.g. Scope height, 100yd zero, scope clicks, powder scale, chrony itself

If you throw out your cold bore/fouling shot, what was your ES and Standard Deviation? i.e. were the chrony readings all over the place? Or, just one or two outliers? ...perhaps muzzle blast too close to the chrony

How many shots did you record and were they all within a short period or throughout the day?

Did lighting change e.g. clouds vs sun during the chrony session?

Are you letting some of the cartridges sit in the sun or hot chamber which would increase MV?

Do you have a known good load/rifle to fire across the chrony as a baseline?

-- richard
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  #11  
Old 04-11-2012, 09:19 AM
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Join Date: Mar 2012
Location: BLACK HILLS SD
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Re: 7 saum unexpected velocity

I will try to shoot some 180s across the chony today. I will bring my 6mm dasher to shoot and make sure my chrony hasnt went bad. I will post the results when i get them. Thanks for the help everyone
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  #12  
Old 04-11-2012, 01:58 PM
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Join Date: Oct 2010
Location: Washington/Canadian border
Posts: 113
Re: 7 saum unexpected velocity

How far was your chrono set up? When I first got my chrono I didn't know it was supposed to be 10 ft away from the barrel and was gettin 4700 fps with 140 gr amax in my .260.
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  #13  
Old 04-11-2012, 03:17 PM
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Join Date: Mar 2012
Location: BLACK HILLS SD
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Re: 7 saum unexpected velocity

I think i am getting closer to finding my rifles happy place. I set up today with the chrony at 10ft from the muzzle. I brought my 6 dasher as a baseline for the chrony speeds. It shot a nice little ragged hole with velocity for 5 shots being 3083,3086,3097,3071,and 3068. This is normal for this gun and the jbm trajetory matches these numbers well.

Now for the 7saum.i loaded 5 180 vlds at the original 54.5 grains of h4350 and the velocitys were 3057,3000,3093,3123,and 3118. These produced a 100 yd group around 3/4".

I also loaded 5 180 vlds with 52.5 grains of h4350. The velocitys came in at 2941,2923,2917,2919,2953. This produced a 3/8 inch ragged hole a 100 yds. Extreme spread of 36. I had 5 more rounds at 52 grains with almost identical results.

This seems like a lot of speed for 52.5 grains of powder but if the trajetory matches it i guess that will be ok.

Would you guys accept an extreme spread of 36 or change primers or any other tricks to lower the extreme spread? Accuracy seems to be good here. I really dont want to wear this barrel out before i get it tuned.
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  #14  
Old 04-11-2012, 03:19 PM
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Join Date: Mar 2012
Location: BLACK HILLS SD
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Re: 7 saum unexpected velocity

P.s. All above loads were shot with cci 250 primers.
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