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Old May 21, 2012, 10:10 AM   #1
thump_rrr
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Question about the temperature sensitivity of Varget

I have a Savage 10BA which I bought last fall.
Up to now I've been shooting my handloads using range pickup brass with great success.

All my brass was once fired and separated by headstamp.
The brass was full length sized and had the primer pockets uniformed, flash holes deburred, trimmed to length, chamfered then weighed in .0.5gr lots by weight.

I then fire formed the brass in my rifle and started load development.

In both Winchester and Federal cases using 180gr SMK's I was able to achieve 0.5 moa accuracy using 40.9gr of Varget which I chronographed at 2550fps give or take.
This was in 40F weather.

Last week I bought a box of Lapua brass and did a ladder test along with 30 rounds of 40.9gr and 41.2gr which worked well for me in Win and FC brass.
The ambient temperature was 80F and at the max load in the Sierra manual which is 41.7gr I was only able to achieve 2390fps.
The ladder test seemed inconclusive. The first 4 rounds began stringing vertically then for some reason the next 3 rounds not only leveled off but had nearly identical velocity out of the chronograph which I can't explain why.

Is this due to the ambient temperature or more to do with case volume?
The weight of the Lapua brass is nearly identical to the FC brass and heavier than the Winchester brass by nearly 30gr.
Should I keep pushing the load till I see pressure signs and do another ladder test?

Last edited by thump_rrr; May 21, 2012 at 06:15 PM.
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Old May 21, 2012, 10:34 AM   #2
mrawesome22
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Velocity dropped over 1000fps?

30 grain difference in case weight?

Sounds like your scale is majorly out of whack.

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Old May 21, 2012, 11:58 AM   #3
totaldla
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I'll assume "1490" was a typo - you meant "2490".

Your 60fps variation could easily be from your brass switch alone. And some chronographs vary slightly with position of the sun (time of day). And Varget will vary a small amount over a 40*F temp swing, but my guess is that the brass was the biggest factor.
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Old May 21, 2012, 03:26 PM   #4
Jimro
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If I remember correctly (and that is a big if) Varget will gain about 15 fps from 0 F to 100 F. So going from 40 to 80 should give you a gain of about 6 fps.

Changing brass is likely the cause of your drop in velocity. The vertical stringing with a "new" load is likely your barrel settling into fouling. At this point I would say to do the test again with a fouled barrel to see how it performs for you.

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Old May 21, 2012, 06:12 PM   #5
thump_rrr
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Sorry for the typo. I corrected it
The actual velocity is 2390 fps with 41.7gr of Varget over a 180gr SMK using Lapua cases in 80F weather.
This is compared to 2550 fps with 40.9gr of Varget over a 180gr SMK using
FC cases in 40F weather.

Last edited by thump_rrr; May 21, 2012 at 06:17 PM.
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Old May 22, 2012, 09:58 PM   #6
Bush Pirate
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Did you use the same primers?
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Old May 22, 2012, 10:10 PM   #7
thump_rrr
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Yup BR-2 primers were used for both loads.
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Old May 23, 2012, 11:52 PM   #8
dacaur
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Varget is extremely temperature stable, your velocities shouldnt vary more than 10fps between those two temps, assuming everything else being the same (what I have heard is about .2-.25fps per degree F), and #2, your hot weather velocities should be HIGHER than the cold weather velocities, again, assuming everything else is the same.....

I think its safe to say we can rule out the powder being the cause. (which rules out the ambient temp)

You simply cannot directly compare results achived using different brands of brass

My guess is the fact that you used different cases is the factor you are looking for.
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