Varget and Environmental Effects?

[neeltburn]

On Wednesday I took my Savage Model 10 308 to the range to do some load testing. I worked up .5 grain steps from 42.5 to 44 grains of Varget. Noting Velocity and accuracy. New Winchester Brass Fed GMM Primer. 175 SMKs. Seated at 2.80 in. Best result for both accuracy and velocity was 44.0 of Varget at 2747 (5 shot ave) SD was 4.69 and ES was 12.49 and no signs up pressure with this load. So last night I loaded up 25 more of the 175s and 44.0gn of Varget in new Win. brass. same as above. And my above results changed and quite a bit. here is my Data for comparison.


10-9-2013 (clean bore)
175 SMK w/ 44.0 Varget

Temp 69* Hum 59% Baro Press. 30.21

1st group not suppressed.

Ave 2748
ES 11.87
SD 6.92

2nd Group Suppressed ( For what ever reason I shoot the rifle much better with the can) This was a much tighter group measured .574

AVE 2747
ES 12.49
SD 4.69

Today 10-12-2013 ( 43 rounds fired before today)
Everything shot suppressed.

New Win brass ( same Lot #) 175smk ( same box) Same 44.0gn Varget and same Fed GMM primer.

Temp 59* 88% Hum Baro Press 30.06

Group 1

Ave 2671
ES 36.56
SD 15.26

Group 2

Ave 2669
ES 18.31
SD7.54

Checked weather
Temp 64* Hum. 78% and Baro Press 30.08

Group 3

Ave 2665
ES 30.02
SD 11.35

Group 4 ( Best group of .74)

Ave 2670
ES 30.00
SD 11.00

The accuracy is more than likely me, but I am concerned about the velocity, if today were a match again I would be SOL using the previous gather data. ( I would never go to a match off 1 5 round group) but I had hope to confirm the data I gathered on Wednesday. What and I missing?

 

[Trevor300wsm]

Most likely it's the chronograph. Did you have different lighting conditions? Sunny or cloudy? High noon or sun up/sun down? Chronographs will give you a good idea, but you always want to verify at distance.

 

[neeltburn]

Most likely it's the chronograph. Did you have different lighting conditions? Sunny or cloudy? High noon or sun up/sun down? Chronographs will give you a good idea, but you always want to verify at distance.

Something very obvious just occurred to me. Today it was in the shade last time it was in more direct sun light..

 

[Trevor300wsm]

That is most likely your problem. Chronos can be very light sensitive. When I'm going to chrono a load I always try to do it around 11am-1pm on a sunny day. It's not that this is better than a different time, it's just that it keeps it consistant everytime.

 

[BCP]

2740 sounds too fast for that load.

I made some up just like that except with a CCI primer and 2600-2650 is much more realistic for your typical 24-26" factory barrel.

 

[VTSEAL]

If you do end up with too much velocity variation based on temperature swings, give the IMR 8208 XBR powder a try. It was designed to be a temperature stable Varget according to Hodgon.
SHOT Show Report: Chris Hodgdon Sets the Record Straight Regarding IMR 8208 XBR « Daily Bulletin

 

[Joop]

2740 sounds too fast for that load.

I made some up just like that except with a CCI primer and 2600-2650 is much more realistic for your typical 24-26" factory barrel.

+1

I have a 10FP with a 24" barrel and have shot the 175 SMK and 178 over 44.0gr. Varget. I usually get around 2650 with this load. I would also guess that the chronograph is the issue, since mine does EXACTLY the same thing. In direct sunlight, it runs about 100fps faster. I've made it a point to shoot in the shade, or when it's overcast, as the velocities it gives under those conditions seem to jive better with my "bullets on paper" results at various ranges.

 

[neeltburn]

+1

I have a 10FP with a 24" barrel and have shot the 175 SMK and 178 over 44.0gr. Varget. I usually get around 2650 with this load. I would also guess that the chronograph is the issue, since mine does EXACTLY the same thing. In direct sunlight, it runs about 100fps faster. I've made it a point to shoot in the shade, or when it's overcast, as the velocities it gives under those conditions seem to jive better with my "bullets on paper" results at various ranges.

This makes since to me.. Since I was pushed 175s 2700 with 44.5 gr before I got into this lot of Varget. Back at it in the morning with 44.0gn and 44.3 trying to creep back to 2700 slowing with out pressure sign.


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[Wildboarem]

U can also pull your sunscreens in cloudy or overcast conditions and replace them when it's sunny. Their purpose is to contrast the bullet as it flies over the "reader". Works for me. Get consistent results regardless of conditions.

 

[neeltburn]

U can also pull your sunscreens in cloudy or overcast conditions and replace them when it's sunny. Their purpose is to contrast the bullet as it flies over the "reader". Works for me. Get consistent results regardless of conditions.

I did this as well. I think the biggest factor that helped me was replacing the battery in the Chrony.


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[TRAAV]

Stop shooting them across the chrony. I think you are going to drive yourself nuts with that thing. Use it to check your ES and SD And get a base line velocity. Then go put some rounds down range at distance and get your dope from there. In my experience (which isn't a ton) the chrony is only going to get your close anyway and from day to day with lighting conditions it will change.

 

[Deadshot2]

That is most likely your problem. Chronos can be very light sensitive. When I'm going to chrono a load I always try to do it around 11am-1pm on a sunny day. It's not that this is better than a different time, it's just that it keeps it consistant everytime.

I keep a box of factory ammo around just for "Chrono Verification". One round over the box of the factory ammo which I have tested many times before. Whatever reading I get I use it as a correction factor. A batch of Hornady TAP 168 gr has been as consistent as any factory ammo I've encountered. If my shot reads high I subtract that amount from subsequent shots of my handloads on that day. Next day it might be low and I just add the error.

Seems to work OK. Whenever I change range using the new ballistics calcs the shots are right on. Unless you have some way of checking the accuracy of a chronograph in varying environmental conditions it's tough to get readings you can absolutely trust. The method I use may not meet lab standards but it sure seems to level out all the lighting induced speed changes.

Of course I could probably spring for a PVM or Magneto Speed and eliminate the environmental issues. Problem there is that I just recently slipped a brand new barrel and truing job past my wife. Might not be so lucky with a new chrono

 

[Pinecone]

Or get a better chronograph.

 

[neeltburn]

Or get a better chronograph.

Think about a Magnetospeed.


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[Pinecone]

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