Powder lot variations

[Driftertank]

Pressure variations between different lots of the same powder aren't a new thing, but I wanted to share an experience regarding the biggest variation I've personally seen so far.

I did some load workups for my wife's new 6.5 PRC, using Hodgdon H-1000, Norma brass, Norma 143gr Bondstrike bullets.

After I initially did this workup, I settled on 58.1gr for charge weight, then bumped seating depth in and out a little to finalize a load. Ended up with a load that was pretty easily sub-MOA.

Went back to the bench, opened up a new jar of H1000, and loaded up 50 rounds. All good, right?

Next trip to the range though, I decided to check zero on the wife's rifle. Target up at 200yd, 3 rounds on paper...about a 3" group. Huh...

I let the rifle get dead cold again, broke out the chrony, and sent 3 more. Another disappointing group, and a smoking gun (so to speak)...velocity average of about 2920, rather than the 2990 I was seeing previously.

This also checks with another issue I had had; namely that a handful of rounds I had worked up using an established load in my 7mmRM, that had long been a 3/4MOA load, had not only grouped poorly, but had very difficult extraction when using the same jar of powder I had used to work up the PRC load.

By my calculations, the velocity difference between one jar and another of the same powder was about 2.5%. This is a significant increase, and far more than I have ever previously seen changing lots before. The jar in question was also old enough (though still sealed) to have been an older style of label than the current "Hodgdon Extreme" powders. It was dug out by my father-in-law when I mentioned the difficulty I was having sourcing enough powder these days.

However, that particular pound of powder is now gone, and I WAS able to get in an order for a keg from Powder Valley in the 7 minute window between getting the in-stock notification email, and them being sold out again...

So anyway, I have a little bit of testing and returning to do now, but once that's done I should be good for quite some time.

Just thought I'd share the reminder that, even if you haven't had issues with significant variations between powder lots, they do happen, and it's not a bad practice to at least sample and confirm a load with a new lot# before you load up a bunch of rounds.

 

[FROGO207]

I think that the makers do us solid keeping the variations to the small amount they do. You always need to do at least an abreviated workup when changing propellants. Also a good reason to buy in bulk and use the same lot numbers when possible. I find when using larger volumes of propellant a variation is more pronounced. Handgun ammo shows smaller variations when I test my ammo for velocity with different lots.

 

[Hooda Thunkit]

I rarely purchase pound bottles of powder, unless I can get multiples of the same lot number. I generally try to get at least a 4lb jug.

Especially with rifle powders, it's just not worth working up a load with a single pound.

I have been known to blend bottles of the same powder with different lot numbers into a homogeneous 'lot'. That way I have enough that lot to make it worth building a load.

 

[Driftertank]

My previous loadings, I've managed to grab at least 3-4 singles at a time, all from the same lot number. I've also changed lots and had small enough variations that it didn't justify much change to my loads, as the velocity changes were within previous ES brackets.

Like I said, the old single was almost a desperation play. I was down to about 1lb before it was given to me. I still kick myself for passing up a keg I saw on the shelf about 5 years ago because it was $10 more than the shop across town usually carried it; that was the last time I saw H1000 locally that didn't have a will-call tag on it.

 

[kalielkslayer]

Just yesterday I was using W760. I have 6 lbs, all singles. All I could get when I found out it was the same as H414.

I bought all these with a 2 lb limit, different vendors. But all within a month if each other. I haven’t checked lot numbers but the thought I had as I was pouring the powder into the trickler was “Should I just mix all of these and put them back in the jars?” Reason I thought that was I thought I had a jar I opened recently but I checked the seal and all of them appeared to be new. After I filled the tumbler, I saw the opened one on the top shelf.

I know you aren’t supposed to mix powders, but same powder, different lots?

 

[Slamfire]

Powder lot variance is real. So is primer variance and different brands of bullets print to a different location, even though the weight is the same.

The one thing that shooters never acknowledge, is shooter variance. Shoot enough small bore prone, and you will see the point of impact change based on your position on the stock, how hard you hold the rifle, and how tight the sling. I also see flinches. Smallbore prone is unforgiving towards sight alignment, position, and trigger pull errors, and because the rifle does not recoil hard, the shooter will begin to observe things that blast and recoil hide in a centerfire.

You will see some of these things in Bullseye Pistol, where you shoot with one hand. It is surprising to see the point of impact change with a pistol when I hold the pistol with a "normal" grip, versus a "monster grip". If only I could stop flinching in Bullseye pistol, I would see other things.

 

[murray brook]

Powder lot variance is real

Most certainly true. About 20 yrs ago I was using H-450 in my 270 Weatherby mag. When I changed lots there was a 5 grain difference between lots. Lucky for me that I went from a fast lot to a slow one. Later when Hodgdon discontinued 450 I read that the main reason for this was there was to much lot to lot variation.