Question about the temperature sensitivity of Varget

[thump_rrr]

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?

 

[MtnCreek]

The ambient temperature was 80F and at the max load in the Sierra manual which is 41.7gr I was only able to achieve 1490fps.

Check your velocity.

Does the Sierra manual spec the brass they used?

 

[Smokey Joe]

Chrono...

Thump-rr--Agree with Mtn Creek here--With that huge a difference in velocity, my first suspect in this crime would be a bad chrono reading.

Re: temperature sensitivity: Varget is one of the Hodgdon Extreme series of powders, which are noted for being particularly INsensitive to temperature changes. That's one of this powder's main selling points. Well, that, and that it makes nice accurate loads in a variety of cartridges.

You didn't state what cartridge we're discussing, here.

The vertical stringing I can't comment on--too many other variables.

Lapua brass is some of the most uniform there is, straight from the factory box. (Shrug. Head scratch.)

I guess that, were I you, I'd start by checking out my chronograph. And once the brass is fired in your rifle, I'd be neck-sizing it rather than FL sizing.

You seem to have at least 3 different, interlocking, problems. Good luck on getting it all sorted out.

 

[thump_rrr]

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.

 

[Ol` Joe]

Pressure goes up with temp not down, and velocity usually follows the same path. Varget is very temp stabile in the 308 and I doubt it is the problem.

I`d suspect the crono is acting up or doesn`t like the lighting you had later in the day. The position of the light comes from can affect the readings in my limited experiances with them

 

[evan price]

You have two different charges in two different case brands on two different days with two different weather conditions.

I would start by eliminating the variables and start over. One brand of case, the same day, and run your ladder again with stepping charges.

Anything else is idle speculation.

 

[ArchAngelCD]

You also didn't mention accuracy. I would focus more on accuracy than velocity.

 

[GJgo]

I assume you have a 308 although you didn't say. If you want to shoot them that slow I'd go to a slower powder for more case fill. The Sierra 308 loads are sandbagging for Varget by 3-4 grains in a modern action.

The go-to load for a modern 308 w/ Varget & 175 SMK or 178 Amax is 43.5-45gr depending on brass, primer, etc.. Don't take my word for it though, go do some research at sniper's hide forum.

 

[Marlin 45 carbine]

seems I read varget is better in a compressed load. I have'nt loaded any of it in my '06 though

 

[Hondo 60]

Ambient temp may affect speed a bit, but did you consider barrel temp?

When firing multiple shots, you will see a difference if the barrel gets very hot.

Just something else to think about.