Chasing Load w/ New Varget Lot?

[woojos]

Long story short is I used the last bit of an old lot and went into a new lot of 8-1lbers. Powder is Varget. The old lot I was using was probably of a more recent manufacturer date than the lot I switched too.

The old lot was averaging 2744 w/ a SD of 6. The new lot was averaging 2714 w/ a SD of 7. Bullet was a 175 SMK in once fired Lapua brass, non-annealed, loading to 2.8" OAL w/ 44.4 gr measured +/- .02gr on Gempro. Velocity measurements were taken from a Magnetospeed.

This is a mean difference of 29 fps.

Rifles were newly cleaned, w/ 4 foulers each, and the new lot was shot after the old lot, so there was additional fouling.

The old lot was bugholing. The new lot is plenty accurate, but not quite as tight. Both shot to roughly same POI out of my .308.

I also shot some of the new lot in my .223 which led to some dispersion in groupings at 100 yard. I also noticed a POI shift of ~1.8" vertical, but I've noticed my scope not holding zero on last 2/4 range outings on this rifle. This could be due to other factors and I'll get to the bottom of it sooner or later, but at this point the lot variation is the most likely culprit.

Any recommended courses of action?

 

[Cape Fear]

The old lot was bugholing. The new lot is plenty accurate, but not quite as tight. Both shot to roughly same POI out of my .308.

Based on the above, I would roll with it. But then again, I have a full-time job and kids at home, so time & money are tight. Also I bang steel, so if it will still hold sub .75 MOA or so I am not going to invest the effort to bring it back to bugholing. JBM calls for 0.9 MOA more drop at 1000 with the new speed. I say get some real dope on the new lot of powder and let it ride.

If you are shooting paper for small groups, go back to load development I guess.

 

[ShtrRdy]

step the load up to give you velocity like you were getting before. Hopefully that'll end up in the sweet spot you had.

 

[6brshooter]

I'd either run it like it is or bump it up to old load velocity. I would be more concerned with a scope not holding zero or wandering , effecting accuracy then 29 fps difference. That's just me though.

 

[BapZander]

2744 / 2714 = 1.01. for a quick test, bump the charge weight up 1%, load 5, and test velocity vs old lot. Probably gtg.

 

[Fred_C_Dobbs]

If the current bottle has been open for some time, my hunch is the powder might have absorbed a bit of moisture from the air. Smokeless gunpowder is highly hydrophillic (it LOVES to suck up water), so what used to be 44.4 grains of powder now might be 44.2 grains of powder and 0.2 grains of absorbed water. With no observable difference.

If that's the case, try putting some desiccant in the bottle. If you had 1-lb bottles, you could make do with a few of the small free packets like come with most every electronic gizmo you buy (after drying them in the oven), but I don't think those small free jobbies will cut it in an 8-lb jar.

I bought something similar to this to use for this very purpose, only they don't seem to carry them any more where I got mine (Cheaper Than Dirt). Ten bucks isn't a huge investment, and they're WAY oversized for this job. I cut mine in half and sewed each half closed, making 20 packets each rated to 2.5-3.5 cu. ft. And they're 'rechargeable.'

Throw one in your bottle and give it a couple or three days to work. If it's water to blame, your should see your MV go up every day, up until it's bone dry.


However, if that's a freshly-opened bottle, it might just be differences in the lots of powder. Add charge weight to bring the MV back up to where it was with the old bottle. Even though this one might be a touch "under-strength" compared to the other, it is Varget, and they're NOT going to futz with the pressure curve. So if you match the MV, the dwells should also match, which should put you back on the original accuracy node.

 

[woojos]

The new lot is a freshly opened bottle.

If anything, I thought the old lot may have dried out a bit from factory condition but I absolutely nothing about powder manufacturing. The smell wasn't as strong and I noticed the color may have tinged to a duller bronze versus the factory grey, like the few spilled extrudes sitting on my loading bench.

I was hoping people would say to up the charge a bit to match velocities and see what happens, as this would probably be easiest solution.

The scope wondering is probably just me and my inattention to detail. I set it 1/2 mil low = 1.8" @ 100 for load development to not shoot out my aiming point and may have moved it back at range, then again when I got home. I've been screwing with it, so I think the scope/rifle is fine and it's me being a putz.

Thanks for the replies.

 

[gstaylorg]

As a general rule of thumb, any time you switch lots of powder, be prepared to redo load development at some level. If the lots seem reasonably close, simply finding the charge weight that generates your velocity with the previous lot is usually sufficient as mentioned above. If there is a large difference, you may need to do an abbreviated (or even full blown) test series to get back to where it was with the old lot, just to be sure you're in the middle of the window.